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Angular Stored XSS Vulnerability via SVG Animation, SVG URL and MathML Attributes

High severity GitHub Reviewed Published Dec 1, 2025 in angular/angular • Updated Dec 3, 2025

Package

npm @angular/compiler (npm)

Affected versions

>= 21.0.0-next.0, < 21.0.2
>= 20.0.0-next.0, < 20.3.15
>= 19.0.0-next.0, < 19.2.17
<= 18.2.14

Patched versions

21.0.2
20.3.15
19.2.17

Description

A Stored Cross-Site Scripting (XSS) vulnerability has been identified in the Angular Template Compiler. It occurs because the compiler's internal security schema is incomplete, allowing attackers to bypass Angular's built-in security sanitization. Specifically, the schema fails to classify certain URL-holding attributes (e.g., those that could contain javascript: URLs) as requiring strict URL security, enabling the injection of malicious scripts.

Additionally, a related vulnerability exists involving SVG animation elements (<animate>, <set>, <animateMotion>, <animateTransform>). The attributeName attribute on these elements was not properly validated, allowing attackers to dynamically target security-sensitive attributes like href or xlink:href on other elements. By binding attributeName to "href" and providing a javascript: URL in the values or to attribute, an attacker could bypass sanitization and execute arbitrary code.

Attributes confirmed to be vulnerable include:

  • SVG-related attributes: (e.g., xlink:href), and various MathML attributes (e.g., math|href, annotation|href).
  • SVG animation attributeName attribute when bound to "href" or "xlink:href".

When template binding is used to assign untrusted, user-controlled data to these attributes (e.g., [attr.xlink:href]="maliciousURL" or <animate [attributeName]="'href'" [values]="maliciousURL">), the compiler incorrectly falls back to a non-sanitizing context or fails to block the dangerous attribute assignment. This allows an attacker to inject a javascript:URL payload. Upon user interaction (like a click) on the element, or automatically in the case of animations, the malicious JavaScript executes in the context of the application's origin.

Impact

When exploited, this vulnerability allows an attacker to execute arbitrary code within the context of the vulnerable application's domain. This enables:

  • Session Hijacking: Stealing session cookies and authentication tokens.
  • Data Exfiltration: Capturing and transmitting sensitive user data.
  • Unauthorized Actions: Performing actions on behalf of the user.

Patches

  • 19.2.17
  • 20.3.15
  • 21.0.2

Attack Preconditions

  • The victim's Angular application must render data derived from untrusted input (e.g., from a database or API) and bind it to one of the unsanitized URL attributes or the attributeName of an SVG animation element.
  • The victim must perform a user interaction (e.g., clicking) on the compromised element for the stored script to execute, or the animation must trigger the execution.

Workarounds

If you cannot upgrade, you can workaround the issue by ensuring that any data bound to the vulnerable attributes is never sourced from untrusted user input (e.g., database, API response, URL parameters).

  • Avoid Affected Template Bindings: Specifically avoid using template bindings (e.g., [attr.xlink:href]="maliciousURL") to assign untrusted data to the vulnerable SVG/MathML attributes.
  • Avoid Dynamic attributeName on SVG Animations: Do not bind untrusted data to the attributeName attribute of SVG animation elements (<animate>, <set>, etc.).
  • Enable Content Security Policy (CSP): Configure a robust CSP header that disallows javascript: URLs.

References

@alan-agius4 alan-agius4 published to angular/angular Dec 1, 2025
Published by the National Vulnerability Database Dec 1, 2025
Published to the GitHub Advisory Database Dec 2, 2025
Reviewed Dec 2, 2025
Last updated Dec 3, 2025

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Network
Attack Complexity Low
Attack Requirements None
Privileges Required Low
User interaction Active
Vulnerable System Impact Metrics
Confidentiality High
Integrity High
Availability High
Subsequent System Impact Metrics
Confidentiality None
Integrity None
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(14th percentile)

Weaknesses

Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. Learn more on MITRE.

CVE ID

CVE-2025-66412

GHSA ID

GHSA-v4hv-rgfq-gp49

Source code

Credits

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