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Server-Side Request Forgery (SSRF) in Angular SSR

High
alan-agius4 published GHSA-q63q-pgmf-mxhr Oct 16, 2025

Package

npm @angular/ssr (npm)

Affected versions

>=19.0.0-next.0 < 19.2.18
>=20.0.0-next.0 < 20.3.6
>=21.0.0-next.0 < 21.0.0-next.8

Patched versions

19.2.18
20.3.6
21.0.0-next.8

Description

Impact

The vulnerability is a Server-Side Request Forgery (SSRF) flaw within the URL resolution mechanism of Angular's Server-Side Rendering package (@angular/ssr).

The function createRequestUrl uses the native URL constructor. When an incoming request path (e.g., originalUrl or url) begins with a double forward slash (//) or backslash (\\), the URL constructor treats it as a schema-relative URL. This behavior overrides the security-intended base URL (protocol, host, and port) supplied as the second argument, instead resolving the URL against the scheme of the base URL but adopting the attacker-controlled hostname.

This allows an attacker to specify an external domain in the URL path, tricking the Angular SSR environment into setting the page's virtual location (accessible via DOCUMENT or PlatformLocation tokens) to this attacker-controlled domain. Any subsequent relative HTTP requests made during the SSR process (e.g., using HttpClient.get('assets/data.json')) will be incorrectly resolved against the attacker's domain, forcing the server to communicate with an arbitrary external endpoint.

Exploit Scenario

A request to http://localhost:4200//attacker-domain.com/some-page causes Angular to believe the host is attacker-domain.com. A relative request to api/data then becomes a server-side request to http://attacker-domain.com/api/data.

Patches

  • @angular/ssr 19.2.18
  • @angular/ssr 20.3.6
  • @angular/ssr 21.0.0-next.8

Mitigation

The application's internal location must be robustly determined from the incoming request. The fix requires sanitizing or validating the request path to prevent it from being interpreted as a schema-relative URL (i.e., ensuring it does not start with //).

Server-Side Middleware

If you can't upgrade to a patched version, implement a middleware on the Node.js/Express server that hosts the Angular SSR application to explicitly reject or sanitize requests where the path begins with a double slash (//).

Example (Express/Node.js):

// Place this middleware before the Angular SSR handler
app.use((req, res, next) => {
  if (req.originalUrl?.startsWith('//')) {
    // Sanitize by forcing a single slash
    req.originalUrl = req.originalUrl.replace(/^\/\/+/, '/');
    req.url = req.url.replace(/^\/\/+/, '/');
  }
  next();
});

References

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 None
User interaction None
Vulnerable System Impact Metrics
Confidentiality High
Integrity None
Availability None
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:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

CVE ID

CVE-2025-62427

Weaknesses

Server-Side Request Forgery (SSRF)

The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination. Learn more on MITRE.

Credits