Angular SSR: Open Redirect and Request Steering via Encoded X-Forwarded-Prefix

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

The Angular SSR is a server-rise rendering tool for Angular applications. From 19.0.0-next.0 to before 19.2.25, 20.3.25, 21.2.9, and 22.0.0-next.7, a vulnerability exists in the X-Forwarded-Prefix header processing logic within Angular SSR. The internal validation mechanism fails to properly account for URL-encoded characters, specifically dots (%2e%2e). This allows an attacker to bypass security filters by injecting encoded path traversal sequences that are later decoded and utilized by the application logic. When an Angular SSR application is configured to trust proxy headers and is deployed behind a proxy that forwards the X-Forwarded-Prefix header without prior sanitization, an attacker can provide a payload such as /%2e%2e/evil. This vulnerability is fixed in19.2.25, 20.3.25, 21.2.9, and 22.0.0-next.7.

Source published

13 May 2026 21:23:59 UTC

Source modified

14 May 2026 13:35:18 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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CVSS 4.0 · 6.9 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N

The Angular SSR is a server-rise rendering tool for Angular applications. From 19.0.0-next.0 to before 19.2.25, 20.3.25, 21.2.9, and 22.0.0-next.7, a vulnerability exists in the X-Forwarded-Prefix header processing logic within Angular SSR. The internal validation mechanism fails to properly account for URL-encoded characters, specifically dots (%2e%2e). This allows an attacker to bypass security filters by injecting encoded path traversal sequences that are later decoded and utilized by the application logic. When an Angular SSR application is configured to trust proxy headers and is deployed behind a proxy that forwards the X-Forwarded-Prefix header without prior sanitization, an attacker can provide a payload such as /%2e%2e/evil. This vulnerability is fixed in19.2.25, 20.3.25, 21.2.9, and 22.0.0-next.7.

Source published

May 13, 2026, 9:23:59 PM (timezone not stated)

Source modified

May 14, 2026, 1:35:18 PM (timezone not stated)

Observed here

28 Oct 2026 06:07:37 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 4.0 · 6.9 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N

The Angular SSR is a server-rise rendering tool for Angular applications. From 19.0.0-next.0 to before 19.2.25, 20.3.25, 21.2.9, and 22.0.0-next.7, a vulnerability exists in the X-Forwarded-Prefix header processing logic within Angular SSR. The internal validation mechanism fails to properly account for URL-encoded characters, specifically dots (%2e%2e). This allows an attacker to bypass security filters by injecting encoded path traversal sequences that are later decoded and utilized by the application logic. When an Angular SSR application is configured to trust proxy headers and is deployed behind a proxy that forwards the X-Forwarded-Prefix header without prior sanitization, an attacker can provide a payload such as /%2e%2e/evil. This vulnerability is fixed in19.2.25, 20.3.25, 21.2.9, and 22.0.0-next.7.

Source published

13 May 2026 22:16:44 UTC

Source modified

26 Oct 2026 14:10:00 UTC

Observed here

27 Oct 2026 11:12:09 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · [email protected] · Secondary · 6.9 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

CVSS 3.1 · [email protected] · Primary · 6.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

### Description A vulnerability exists in the `X-Forwarded-Prefix` header processing logic within Angular SSR. The internal validation mechanism fails to properly account for URL-encoded characters, specifically dots (`%2e%2e`). This allows an attacker to bypass security filters by injecting encoded path traversal sequences that are later decoded and utilized by the application logic. When an Angular SSR application is configured to trust proxy headers and is deployed behind a proxy that forwards the `X-Forwarded-Prefix` header without prior sanitization, an attacker can provide a payload such as `/%2e%2e/evil`. The vulnerability manifests in two ways: - Open Redirect: The application processes a redirect (e.g., router `redirectTo`). The decoded traversal payload manipulates the Location header, forcing the browser to an unintended path or external domain. - Server-Side Request Steering: The manipulated prefix is used as the base path for server-side `HttpClient` requests. This causes the server to make requests to unintended internal paths or external endpoints. ### Attack Preconditions - The application must use Angular SSR. - The application must perform internal redirects or use relative URLs in server-side `HttpClient` requests. - The upstream infrastructure (Reverse Proxy/CDN) must pass the `X-Forwarded-Prefix` header to the SSR process without stripping or sanitizing it. ### Workarounds Until the patch is applied, developers should manually sanitize the `X-Forwarded-Prefix` header in their `server.ts`. The workaround involves decoding the component to catch encoded traversal attempts before normalization: ```ts app.use((req, res, next) => { let prefix = req.headers['x-forwarded-prefix']; if (Array.isArray(prefix)) prefix = prefix[0]; if (prefix) { try { // Decode the prefix to catch encoded characters like %2e (dots) const decodedPrefix = decodeURIComponent(prefix); // Sanitize: remove traversal attempts and ensure a safe leading slash req.headers['x-forwarded-prefix'] = decodedPrefix .replace(/\.\./g, '') // Remove any dot-dot sequences .replace(/^[/\\]+/, '/'); // Ensure it starts with exactly one slash } catch (e) { // If decoding fails, remove the potentially malicious header entirely delete req.headers['x-forwarded-prefix']; } } next(); }); ``` ### Configuring Trusted Proxy Headers By default, Angular ignores all X-Forwarded-* headers. If your application is behind a trusted reverse proxy (like a load balancer) that sets these headers, you can configure Angular to trust them. You can configure trustProxyHeaders when initializing the application engine: ```ts const appEngine = new AngularAppEngine({ // Trust specific headers trustProxyHeaders: ['x-forwarded-host', 'x-forwarded-proto', 'x-forwarded-prefix'], }); const nodeAppEngine = new AngularNodeAppEngine({ // Trust all X-Forwarded-* headers trustProxyHeaders: true, }); ``` ### Patches - 22.0.0-next.7 - 21.2.9 - 20.3.25 - 19.2.25 ### Resources - https://github.com/angular/angular-cli/pull/33031 - https://angular.dev/best-practices/security#configuring-trusted-proxy-headers

Source published

6 May 2026 23:42:10 UTC

Source modified

14 May 2026 20:50:01 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V4 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N

Publisher rating · MODERATE