{"id":"CVE-2026-33397","aliases":["GHSA-vfx2-hv2g-xj5f"],"url":"https://o3.security/vulnerability/CVE-2026-33397","summary":"Angular SSR Vulnerable to Protocol-Relative URL Injection via Single Backslash Bypass","details":"The Angular SSR is a server-rise rendering tool for Angular applications. Versions on the 22.x branch prior to 22.0.0-next.2, the 21.x branch prior to 21.2.3, and the 20.x branch prior to 20.3.21 have an Open Redirect vulnerability in `@angular/ssr` due to an incomplete fix for CVE-2026-27738. While the original fix successfully blocked multiple leading slashes (e.g., `///`), the internal validation logic fails to account for a single backslash (`\\`) bypass. When an Angular SSR application is deployed behind a proxy that passes the `X-Forwarded-Prefix` header, an attacker provides a value starting with a single backslash, the internal validation failed to flag the single backslash as invalid, the application prepends a leading forward slash, resulting in a `Location` header containing the URL, and modern browsers interpret the `/\\` sequence as `//`, treating it as a protocol-relative URL and redirecting the user to the attacker-controlled domain. Furthermore, the response lacks the `Vary: X-Forwarded-Prefix` header, allowing the malicious redirect to be stored in intermediate caches (Web Cache Poisoning). Versions 22.0.0-next.2, 21.2.3, and 20.3.21 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.","published":"2026-03-26T13:46:16.145Z","modified":"2026-08-12T03:51:34.756360648Z","cvss":null,"epss":{"score":0.00255,"percentile":0.16786,"asOf":"2026-08-24"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"npm","name":"@angular/ssr","fixedVersion":"22.0.0-next.2"},{"ecosystem":"npm","name":"@angular/ssr","fixedVersion":"21.2.3"},{"ecosystem":"npm","name":"@angular/ssr","fixedVersion":"20.3.21"}],"fix":{"url":"https://github.com/angular/angular-cli/pull/32771","label":"angular/angular-cli#32771"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/33xxx/CVE-2026-33397.json"},{"type":"ADVISORY","url":"https://github.com/advisories/GHSA-xh43-g2fq-wjrj"},{"type":"ADVISORY","url":"https://github.com/angular/angular-cli/security/advisories/GHSA-vfx2-hv2g-xj5f"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-33397"},{"type":"FIX","url":"https://github.com/angular/angular-cli/pull/32771"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:34.756360648Z"}}