Snyk test report

regex = /A(B|C+)+D/
        

$ time node -e '/A(B|C+)+D/.test("ACCCCCCCCCCCCCCCCCCCCCCCCCCCCD")'
        0.04s user 0.01s system 95% cpu 0.052 total
        
        $ time node -e '/A(B|C+)+D/.test("ACCCCCCCCCCCCCCCCCCCCCCCCCCCCX")'
        1.79s user 0.02s system 99% cpu 1.812 total
        

Improper Validation of Specified Index, Position, or Offset in Input

---

Overview

uuid is a RFC4122 (v1, v4, and v5) compliant UUID library.

Affected versions of this package are vulnerable to Improper Validation of Specified Index, Position, or Offset in Input due to accepting external output buffers but not rejecting out-of-range writes (small buf or large offset). This inconsistency allows silent partial writes into caller-provided buffers.

PoC

cd /home/StrawHat/uuid
        npm ci
        npm run build
        
        node --input-type=module -e "
        import {v4,v5,v6} from './dist-node/index.js';
        const ns='6ba7b810-9dad-11d1-80b4-00c04fd430c8';
        for (const [name,fn] of [
          ['v4',()=>v4({},new Uint8Array(8),4)],
          ['v5',()=>v5('x',ns,new Uint8Array(8),4)],
          ['v6',()=>v6({},new Uint8Array(8),4)],
        ]) {
          try { fn(); console.log(name,'NO_THROW'); }
          catch(e){ console.log(name,'THREW',e.name); }
        }"
        

Remediation

Upgrade uuid to version 11.1.1, 14.0.0 or higher.

References

• GitHub Commit
• GitHub Commit
• GitHub Release

---

Inefficient Algorithmic Complexity

---

Overview

js-yaml is a human-friendly data serialization language.

Affected versions of this package are vulnerable to Inefficient Algorithmic Complexity in the storeMappingPair() function in loader.js when handling repeated aliases in merge sequences. An attacker can exhaust CPU resources and significantly degrade service availability by submitting malicious YAML documents.

Remediation

Upgrade js-yaml to version 4.2.0 or higher.

References

• GitHub Advisory
• GitHub Commit

---

Improper Validation of Specified Type of Input

---

Overview

Affected versions of this package are vulnerable to Improper Validation of Specified Type of Input in the calls plugin when handling websocket messages containing malformed msgpack frames. An attacker can cause the server to consume excessive memory and crash by sending specially crafted websocket requests.

Remediation

There is no fixed version for github.com/vmihailenco/msgpack/v5.

References

• GitHub Commit
• Mattermost Security Updates

---

Regular Expression Denial of Service (ReDoS)

---

Overview

foundation-sites is a responsive front-end framework

Affected versions of this package are vulnerable to Regular Expression Denial of Service (ReDoS) due to inefficient backtracking in the regular expressions used in URL forms.

PoC

https://www.''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
        

Details

Denial of Service (DoS) describes a family of attacks, all aimed at making a system inaccessible to its original and legitimate users. There are many types of DoS attacks, ranging from trying to clog the network pipes to the system by generating a large volume of traffic from many machines (a Distributed Denial of Service - DDoS - attack) to sending crafted requests that cause a system to crash or take a disproportional amount of time to process.

The Regular expression Denial of Service (ReDoS) is a type of Denial of Service attack. Regular expressions are incredibly powerful, but they aren't very intuitive and can ultimately end up making it easy for attackers to take your site down.

Let’s take the following regular expression as an example:

regex = /A(B|C+)+D/
        

This regular expression accomplishes the following:

• A The string must start with the letter 'A'
• (B|C+)+ The string must then follow the letter A with either the letter 'B' or some number of occurrences of the letter 'C' (the + matches one or more times). The + at the end of this section states that we can look for one or more matches of this section.
• D Finally, we ensure this section of the string ends with a 'D'

The expression would match inputs such as ABBD, ABCCCCD, ABCBCCCD and ACCCCCD

It most cases, it doesn't take very long for a regex engine to find a match:

$ time node -e '/A(B|C+)+D/.test("ACCCCCCCCCCCCCCCCCCCCCCCCCCCCD")'
        0.04s user 0.01s system 95% cpu 0.052 total
        
        $ time node -e '/A(B|C+)+D/.test("ACCCCCCCCCCCCCCCCCCCCCCCCCCCCX")'
        1.79s user 0.02s system 99% cpu 1.812 total
        

The entire process of testing it against a 30 characters long string takes around ~52ms. But when given an invalid string, it takes nearly two seconds to complete the test, over ten times as long as it took to test a valid string. The dramatic difference is due to the way regular expressions get evaluated.

Most Regex engines will work very similarly (with minor differences). The engine will match the first possible way to accept the current character and proceed to the next one. If it then fails to match the next one, it will backtrack and see if there was another way to digest the previous character. If it goes too far down the rabbit hole only to find out the string doesn’t match in the end, and if many characters have multiple valid regex paths, the number of backtracking steps can become very large, resulting in what is known as catastrophic backtracking.

Let's look at how our expression runs into this problem, using a shorter string: "ACCCX". While it seems fairly straightforward, there are still four different ways that the engine could match those three C's:

1. CCC
2. CC+C
3. C+CC
4. C+C+C.

The engine has to try each of those combinations to see if any of them potentially match against the expression. When you combine that with the other steps the engine must take, we can use RegEx 101 debugger to see the engine has to take a total of 38 steps before it can determine the string doesn't match.

From there, the number of steps the engine must use to validate a string just continues to grow.

String	Number of C's	Number of steps
ACCCX	3	38
ACCCCX	4	71
ACCCCCX	5	136
ACCCCCCCCCCCCCCX	14	65,553

By the time the string includes 14 C's, the engine has to take over 65,000 steps just to see if the string is valid. These extreme situations can cause them to work very slowly (exponentially related to input size, as shown above), allowing an attacker to exploit this and can cause the service to excessively consume CPU, resulting in a Denial of Service.

Remediation

There is no fixed version for foundation-sites.

References

• GitHub Advisory
• GitHub Issue
• Vulnerable Code

---

CRLF Injection

---

Overview

Affected versions of this package are vulnerable to CRLF Injection via the _multiPartHeader function when untrusted input is provided via field or filename to FormData#append. An attacker can inject additional headers or multipart parts by including carriage returns, line feeds, or double quotes in the input. This can allow the modification or addition of form fields visible to downstream parsers.

PoC

const FormData = require('form-data');
        const form = new FormData();
        form.append('email"\r\nX-Injected: true\r\nfake="', 'user@example.com');
        console.log(form.getBuffer().toString());
        

Remediation

Upgrade form-data to version 2.5.6, 3.0.5, 4.0.6 or higher.

References

• GitHub Commit
• GitHub Commit
• GitHub Commit
• Maintainer's Advisory

---

Cross-site Scripting (XSS)

---

Overview

dompurify is a DOM-only XSS sanitizer for HTML, MathML and SVG.

Affected versions of this package are vulnerable to Cross-site Scripting (XSS) in the IN_PLACE process when attacker-controlled live DOM nodes are sanitized. An attacker can execute arbitrary scripts in the context of the application by passing a manipulated DOM node with a spoofed nodeName property, causing malicious script elements to be retained and executed upon insertion into the document.

PoC

<!doctype html>
        <html><body>
        <script src="dist/purify.js"></script>
        <script>
          const foreign = window.open('about:blank', '_blank', 'noopener=no');
        
          const host = foreign.document.createElement('div');
          const script = foreign.document.createElement('script');
          script.textContent = 'window.__pwned = 1';
          Object.defineProperty(script, 'nodeName', {
            value: 'DIV',
            configurable: true,
          });
          host.appendChild(script);
        
          DOMPurify.sanitize(host, { IN_PLACE: true });
        
          console.log('output:', host.outerHTML);
          // <div><script>window.__pwned = 1</script></div>
        
          window.__pwned = 0;
          document.body.appendChild(host);
          console.log('handler fired:', window.__pwned === 1); // true
        </script>
        </body></html>
        

Details

Cross-site scripting (or XSS) is a code vulnerability that occurs when an attacker “injects” a malicious script into an otherwise trusted website. The injected script gets downloaded and executed by the end user’s browser when the user interacts with the compromised website.

This is done by escaping the context of the web application; the web application then delivers that data to its users along with other trusted dynamic content, without validating it. The browser unknowingly executes malicious script on the client side (through client-side languages; usually JavaScript or HTML) in order to perform actions that are otherwise typically blocked by the browser’s Same Origin Policy.

Injecting malicious code is the most prevalent manner by which XSS is exploited; for this reason, escaping characters in order to prevent this manipulation is the top method for securing code against this vulnerability.

Escaping means that the application is coded to mark key characters, and particularly key characters included in user input, to prevent those characters from being interpreted in a dangerous context. For example, in HTML, < can be coded as &lt; and > can be coded as &gt; in order to be interpreted and displayed as themselves in text, while within the code itself, they are used for HTML tags. If malicious content is injected into an application that escapes special characters and that malicious content uses < and > as HTML tags, those characters are nonetheless not interpreted as HTML tags by the browser if they’ve been correctly escaped in the application code and in this way the attempted attack is diverted.

The most prominent use of XSS is to steal cookies (source: OWASP HttpOnly) and hijack user sessions, but XSS exploits have been used to expose sensitive information, enable access to privileged services and functionality and deliver malware.

Types of attacks

There are a few methods by which XSS can be manipulated:

Type	Origin	Description
Stored	Server	The malicious code is inserted in the application (usually as a link) by the attacker. The code is activated every time a user clicks the link.
Reflected	Server	The attacker delivers a malicious link externally from the vulnerable web site application to a user. When clicked, malicious code is sent to the vulnerable web site, which reflects the attack back to the user’s browser.
DOM-based	Client	The attacker forces the user’s browser to render a malicious page. The data in the page itself delivers the cross-site scripting data.
Mutated		The attacker injects code that appears safe, but is then rewritten and modified by the browser, while parsing the markup. An example is rebalancing unclosed quotation marks or even adding quotation marks to unquoted parameters.

Affected environments

The following environments are susceptible to an XSS attack:

• Web servers
• Application servers
• Web application environments

How to prevent

This section describes the top best practices designed to specifically protect your code:

• Sanitize data input in an HTTP request before reflecting it back, ensuring all data is validated, filtered or escaped before echoing anything back to the user, such as the values of query parameters during searches.
• Convert special characters such as ?, &, /, <, > and spaces to their respective HTML or URL encoded equivalents.
• Give users the option to disable client-side scripts.
• Redirect invalid requests.
• Detect simultaneous logins, including those from two separate IP addresses, and invalidate those sessions.
• Use and enforce a Content Security Policy (source: Wikipedia) to disable any features that might be manipulated for an XSS attack.
• Read the documentation for any of the libraries referenced in your code to understand which elements allow for embedded HTML.

Remediation

Upgrade dompurify to version 3.4.8 or higher.

References

• GitHub Advisory
• GitHub Commit

---

Cross-site Scripting (XSS)

---

Overview

dompurify is a DOM-only XSS sanitizer for HTML, MathML and SVG.

Affected versions of this package are vulnerable to Cross-site Scripting (XSS) in the IN_PLACE function when handling a <template> element containing an element with an attached shadow DOM. An attacker can execute arbitrary scripts in the context of the user by injecting malicious content into the shadow DOM, which is not sanitized and is later executed when the template is cloned and inserted into the page.

Details

Cross-site scripting (or XSS) is a code vulnerability that occurs when an attacker “injects” a malicious script into an otherwise trusted website. The injected script gets downloaded and executed by the end user’s browser when the user interacts with the compromised website.

This is done by escaping the context of the web application; the web application then delivers that data to its users along with other trusted dynamic content, without validating it. The browser unknowingly executes malicious script on the client side (through client-side languages; usually JavaScript or HTML) in order to perform actions that are otherwise typically blocked by the browser’s Same Origin Policy.

Injecting malicious code is the most prevalent manner by which XSS is exploited; for this reason, escaping characters in order to prevent this manipulation is the top method for securing code against this vulnerability.

Escaping means that the application is coded to mark key characters, and particularly key characters included in user input, to prevent those characters from being interpreted in a dangerous context. For example, in HTML, < can be coded as &lt; and > can be coded as &gt; in order to be interpreted and displayed as themselves in text, while within the code itself, they are used for HTML tags. If malicious content is injected into an application that escapes special characters and that malicious content uses < and > as HTML tags, those characters are nonetheless not interpreted as HTML tags by the browser if they’ve been correctly escaped in the application code and in this way the attempted attack is diverted.

The most prominent use of XSS is to steal cookies (source: OWASP HttpOnly) and hijack user sessions, but XSS exploits have been used to expose sensitive information, enable access to privileged services and functionality and deliver malware.

Types of attacks

There are a few methods by which XSS can be manipulated:

Type	Origin	Description
Stored	Server	The malicious code is inserted in the application (usually as a link) by the attacker. The code is activated every time a user clicks the link.
Reflected	Server	The attacker delivers a malicious link externally from the vulnerable web site application to a user. When clicked, malicious code is sent to the vulnerable web site, which reflects the attack back to the user’s browser.
DOM-based	Client	The attacker forces the user’s browser to render a malicious page. The data in the page itself delivers the cross-site scripting data.
Mutated		The attacker injects code that appears safe, but is then rewritten and modified by the browser, while parsing the markup. An example is rebalancing unclosed quotation marks or even adding quotation marks to unquoted parameters.

Affected environments

The following environments are susceptible to an XSS attack:

• Web servers
• Application servers
• Web application environments

How to prevent

This section describes the top best practices designed to specifically protect your code:

• Sanitize data input in an HTTP request before reflecting it back, ensuring all data is validated, filtered or escaped before echoing anything back to the user, such as the values of query parameters during searches.
• Convert special characters such as ?, &, /, <, > and spaces to their respective HTML or URL encoded equivalents.
• Give users the option to disable client-side scripts.
• Redirect invalid requests.
• Detect simultaneous logins, including those from two separate IP addresses, and invalidate those sessions.
• Use and enforce a Content Security Policy (source: Wikipedia) to disable any features that might be manipulated for an XSS attack.
• Read the documentation for any of the libraries referenced in your code to understand which elements allow for embedded HTML.

Remediation

Upgrade dompurify to version 3.4.7 or higher.

References

• GitHub Advisory
• GitHub Commit

---

Trust Boundary Violation

---

Overview

dompurify is a DOM-only XSS sanitizer for HTML, MathML and SVG.

Affected versions of this package are vulnerable to Trust Boundary Violation through the mutation of data.allowedTags or data.allowedAttributes in hooks, which directly alters the global default sets used for sanitization. An attacker can cause persistent changes to the default allow-lists, enabling malicious tags or attributes to bypass sanitization in subsequent calls by injecting payloads that exploit the polluted configuration.

Note:

This is only exploitable if a hook is registered that mutates data.allowedTags or data.allowedAttributes, and later sanitization occurs without explicitly setting restrictive configuration arrays.

PoC

// 1) fresh DOMPurify, default config — script is blocked
        DOMPurify.sanitize('<svg><script>alert(1)</script></svg>');
        // → "<svg></svg>"
        
        // 2) install a hook that mutates data.allowedTags (natural-looking pattern)
        DOMPurify.addHook('uponSanitizeElement', (node, data) => {
          data.allowedTags['script'] = true;
        });
        
        // 3) one sanitize call WITH the hook — script survives (expected during the hook)
        DOMPurify.sanitize('<svg><script>alert(1)</script></svg>');
        // → "<svg><script>alert(1)</script></svg>"
        
        // 4) remove the hook
        DOMPurify.removeAllHooks();
        DOMPurify.clearConfig();
        
        // 5) sanitize attacker content with default config — POLLUTION PERSISTS
        DOMPurify.sanitize('<svg><script>alert(1)</script></svg>');
        // → "<svg><script>alert(1)</script></svg>"  ← script survived without any hook
        
        // 6) the only recovery: create a fresh DOMPurify instance
        const fresh = DOMPurify(window);
        fresh.sanitize('<svg><script>alert(1)</script></svg>');
        // → "<svg></svg>"  ← clean
        

Remediation

Upgrade dompurify to version 3.4.7 or higher.

References

• GitHub Advisory
• GitHub Commit

---

Trust Boundary Violation

---

Overview

dompurify is a DOM-only XSS sanitizer for HTML, MathML and SVG.

Affected versions of this package are vulnerable to Trust Boundary Violation in the sanitize function when handling DOM nodes from a different same-origin realm due to improper realm-bound instanceof checks. An attacker can inject and execute malicious markup by providing specially crafted DOM nodes from a foreign realm, which bypass internal security checks and allow executable content to persist in form attributes, template content, and attached shadow roots.

Remediation

Upgrade dompurify to version 3.4.6 or higher.

References

• GitHub Advisory
• GitHub Commit

---

Prototype Pollution

---

Overview

dompurify is a DOM-only XSS sanitizer for HTML, MathML and SVG.

Affected versions of this package are vulnerable to Prototype Pollution in the IN_PLACE function when sanitizing a root element that is a <form> with event handler attributes and a descendant element whose name attribute matches certain property names checked by _isClobbered. An attacker can cause malicious attributes, such as event handlers or JavaScript URIs, to persist on the root element by crafting a DOM structure where the root is clobbered and then passing it to the sanitizer in IN_PLACE mode. This allows the attacker to execute arbitrary JavaScript or bypass attribute-level defenses when the sanitized node is reinserted into the live document.

Note:

This is only exploitable if the sanitizer is used in IN_PLACE mode on a detached root element that is an HTMLFormElement with a clobber-named child.

PoC

<!doctype html>
        <html><body>
        <script src="dist/purify.js"></script>
        <script>
          const root = document.createElement('form');
          root.setAttribute('onmouseover', 'window.__rooted = 1');
          const clobber = document.createElement('input');
          clobber.setAttribute('name', 'nodeName');
          root.appendChild(clobber);
        
          // typeof root.nodeName === 'object' (an <INPUT> element), not 'string'.
          // _isClobbered fires; _forceRemove(root) becomes a no-op because root.parentNode === null.
          DOMPurify.sanitize(root, { IN_PLACE: true });
        
          console.log('output:', root.outerHTML);
          // <form onmouseover="window.__rooted = 1"><input name="nodeName"></form>
          //  ^^^^^^^^^^^^^^^^^^ event handler survived ^^^^^^^^^^^^^^^^^^
        
          document.body.appendChild(root);
          root.dispatchEvent(new MouseEvent('mouseover', { bubbles: true }));
          console.log('handler fired:', window.__rooted === 1);  // true
        </script>
        </body></html>
        

Details

Prototype Pollution is a vulnerability affecting JavaScript. Prototype Pollution refers to the ability to inject properties into existing JavaScript language construct prototypes, such as objects. JavaScript allows all Object attributes to be altered, including their magical attributes such as __proto__, constructor and prototype. An attacker manipulates these attributes to overwrite, or pollute, a JavaScript application object prototype of the base object by injecting other values. Properties on the Object.prototype are then inherited by all the JavaScript objects through the prototype chain. When that happens, this leads to either denial of service by triggering JavaScript exceptions, or it tampers with the application source code to force the code path that the attacker injects, thereby leading to remote code execution.

There are two main ways in which the pollution of prototypes occurs:

• Unsafe Object recursive merge

• Property definition by path

Unsafe Object recursive merge

The logic of a vulnerable recursive merge function follows the following high-level model:

merge (target, source)
        
          foreach property of source
        
            if property exists and is an object on both the target and the source
        
              merge(target[property], source[property])
        
            else
        
              target[property] = source[property]
        

When the source object contains a property named __proto__ defined with Object.defineProperty() , the condition that checks if the property exists and is an object on both the target and the source passes and the merge recurses with the target, being the prototype of Object and the source of Object as defined by the attacker. Properties are then copied on the Object prototype.

Clone operations are a special sub-class of unsafe recursive merges, which occur when a recursive merge is conducted on an empty object: merge({},source).

lodash and Hoek are examples of libraries susceptible to recursive merge attacks.

Property definition by path

There are a few JavaScript libraries that use an API to define property values on an object based on a given path. The function that is generally affected contains this signature: theFunction(object, path, value)

If the attacker can control the value of “path”, they can set this value to __proto__.myValue. myValue is then assigned to the prototype of the class of the object.

Types of attacks

There are a few methods by which Prototype Pollution can be manipulated:

Type	Origin	Short description
Denial of service (DoS)	Client	This is the most likely attack. DoS occurs when Object holds generic functions that are implicitly called for various operations (for example, toString and valueOf). The attacker pollutes Object.prototype.someattr and alters its state to an unexpected value such as Int or Object. In this case, the code fails and is likely to cause a denial of service. For example: if an attacker pollutes Object.prototype.toString by defining it as an integer, if the codebase at any point was reliant on someobject.toString() it would fail.
Remote Code Execution	Client	Remote code execution is generally only possible in cases where the codebase evaluates a specific attribute of an object, and then executes that evaluation. For example: eval(someobject.someattr). In this case, if the attacker pollutes Object.prototype.someattr they are likely to be able to leverage this in order to execute code.
Property Injection	Client	The attacker pollutes properties that the codebase relies on for their informative value, including security properties such as cookies or tokens. For example: if a codebase checks privileges for someuser.isAdmin, then when the attacker pollutes Object.prototype.isAdmin and sets it to equal true, they can then achieve admin privileges.

Affected environments

The following environments are susceptible to a Prototype Pollution attack:

• Application server

• Web server

• Web browser

How to prevent

1. Freeze the prototype— use Object.freeze (Object.prototype).

2. Require schema validation of JSON input.

3. Avoid using unsafe recursive merge functions.

4. Consider using objects without prototypes (for example, Object.create(null)), breaking the prototype chain and preventing pollution.

5. As a best practice use Map instead of Object.

For more information on this vulnerability type:

Arteau, Olivier. “JavaScript prototype pollution attack in NodeJS application.” GitHub, 26 May 2018

Remediation

Upgrade dompurify to version 3.4.6 or higher.

References

• GitHub Advisory
• GitHub Commit

---

Cross-site Scripting (XSS)

---

Overview

dompurify is a DOM-only XSS sanitizer for HTML, MathML and SVG.

Affected versions of this package are vulnerable to Cross-site Scripting (XSS) in the SAFE_FOR_TEMPLATES function. An attacker can inject template expressions that survive sanitization inside <template> element content by splitting malicious expressions across adjacent text nodes, which are not properly scrubbed. This allows execution of arbitrary code or exfiltration of sensitive data if a downstream template engine evaluates the merged content.

This is only exploitable if both SAFE_FOR_TEMPLATES: true and either RETURN_DOM: true, RETURN_DOM_FRAGMENT: true, or IN_PLACE: true are explicitly set, and the application processes <template>.content with a template engine.

Details

Cross-site scripting (or XSS) is a code vulnerability that occurs when an attacker “injects” a malicious script into an otherwise trusted website. The injected script gets downloaded and executed by the end user’s browser when the user interacts with the compromised website.

This is done by escaping the context of the web application; the web application then delivers that data to its users along with other trusted dynamic content, without validating it. The browser unknowingly executes malicious script on the client side (through client-side languages; usually JavaScript or HTML) in order to perform actions that are otherwise typically blocked by the browser’s Same Origin Policy.

Injecting malicious code is the most prevalent manner by which XSS is exploited; for this reason, escaping characters in order to prevent this manipulation is the top method for securing code against this vulnerability.

Escaping means that the application is coded to mark key characters, and particularly key characters included in user input, to prevent those characters from being interpreted in a dangerous context. For example, in HTML, < can be coded as &lt; and > can be coded as &gt; in order to be interpreted and displayed as themselves in text, while within the code itself, they are used for HTML tags. If malicious content is injected into an application that escapes special characters and that malicious content uses < and > as HTML tags, those characters are nonetheless not interpreted as HTML tags by the browser if they’ve been correctly escaped in the application code and in this way the attempted attack is diverted.

The most prominent use of XSS is to steal cookies (source: OWASP HttpOnly) and hijack user sessions, but XSS exploits have been used to expose sensitive information, enable access to privileged services and functionality and deliver malware.

Types of attacks

There are a few methods by which XSS can be manipulated:

Type	Origin	Description
Stored	Server	The malicious code is inserted in the application (usually as a link) by the attacker. The code is activated every time a user clicks the link.
Reflected	Server	The attacker delivers a malicious link externally from the vulnerable web site application to a user. When clicked, malicious code is sent to the vulnerable web site, which reflects the attack back to the user’s browser.
DOM-based	Client	The attacker forces the user’s browser to render a malicious page. The data in the page itself delivers the cross-site scripting data.
Mutated		The attacker injects code that appears safe, but is then rewritten and modified by the browser, while parsing the markup. An example is rebalancing unclosed quotation marks or even adding quotation marks to unquoted parameters.

Affected environments

The following environments are susceptible to an XSS attack:

• Web servers
• Application servers
• Web application environments

How to prevent

This section describes the top best practices designed to specifically protect your code:

• Sanitize data input in an HTTP request before reflecting it back, ensuring all data is validated, filtered or escaped before echoing anything back to the user, such as the values of query parameters during searches.
• Convert special characters such as ?, &, /, <, > and spaces to their respective HTML or URL encoded equivalents.
• Give users the option to disable client-side scripts.
• Redirect invalid requests.
• Detect simultaneous logins, including those from two separate IP addresses, and invalidate those sessions.
• Use and enforce a Content Security Policy (source: Wikipedia) to disable any features that might be manipulated for an XSS attack.
• Read the documentation for any of the libraries referenced in your code to understand which elements allow for embedded HTML.

Remediation

Upgrade dompurify to version 3.4.8 or higher.

References

• GitHub Advisory
• GitHub Commit

---

Improper Initialization

---

Overview

dompurify is a DOM-only XSS sanitizer for HTML, MathML and SVG.

Affected versions of this package are vulnerable to Improper Initialization in the DOMPurify.setConfig() API when an uponSanitizeAttribute hook is registered that mutates allowedAttributes. An attacker can cause persistent modification of the attribute allowlist by submitting specially crafted content, resulting in unauthorized attributes being permitted in all subsequent sanitization calls.

Remediation

Upgrade dompurify to version 3.4.11 or higher.

References

• GitHub Advisory
• GitHub Commit

---