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Medium, CVSS 6.9amended

Angular SSR has an Open Redirect via X-Forwarded-Prefix

CVE-2026-27738GHSA-xh43-g2fq-wjrj

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (@angular/ssr 21.2.0-rc.1, 21.1.5, 20.3.17, 19.2.21), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • npm @angular/ssr

    Affected
    >= 21.2.0-next.0, < 21.2.0-rc.1>= 21.0.0-next.0, < 21.1.5>= 20.0.0-next.0, < 20.3.17>= 19.0.0-next.0, < 19.2.21
    Fixed in
    21.2.0-rc.1, 21.1.5, 20.3.17, 19.2.21

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
6.9 · 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 · score source
EPSS
  • CVE-2026-27738: 0.35% estimated exploitation activity in the next 30 days; percentile 28.75 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

An Open Redirect vulnerability exists in the internal URL processing logic in Angular SSR. 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 (e.g., `///evil.com`). 1. The application processes a redirect (e.g., from a router `redirectTo` or i18n locale switch). 2. Angular receives `///evil.com` as the prefix. 3. It strips one slash, leaving `//evil.com`. 4. The resulting string is used in the `Location` header. 5. Modern browsers interpret `//` as a protocol-relative URL, redirecting the user from `https://your-app.com` to `https://evil.com`.

Impact This vulnerability allows attackers to conduct large-scale phishing and SEO hijacking: - Scale: A single request can poison a high-traffic route, impacting all users until the cache expires. - **SEO…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

  2. Revision 1 · created ·

    Published from osv record GHSA-xh43-g2fq-wjrj

Agent brief

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# Patch Next advisory brief: CVE-2026-27738

Advisory: Angular SSR has an Open Redirect via X-Forwarded-Prefix
IDs: CVE-2026-27738, GHSA-xh43-g2fq-wjrj
Record: https://patchnext.com/advisories/cve-2026-27738 (revision 2, source checked 25 Oct 2026, 00:30 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.9)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @angular/ssr 21.2.0-rc.1, 21.1.5, 20.3.17, 19.2.21. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @angular/ssr: affected >= 21.2.0-next.0, < 21.2.0-rc.1; >= 21.0.0-next.0, < 21.1.5; >= 20.0.0-next.0, < 20.3.17; >= 19.0.0-next.0, < 19.2.21; fixed in 21.2.0-rc.1, 21.1.5, 20.3.17, 19.2.21

## Suggested inspection (read-only)
- `npm ls @angular/ssr --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on @angular/ssr.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-xh43-g2fq-wjrj (OSV record GHSA-xh43-g2fq-wjrj lists affected ranges: npm @angular/ssr >=21.2.0-next.0 =21.0.0-next.0 =20.0.0-next.0 =19.0.0-next.0 <19.2.21 (fixed))

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