GHSA-c6q7-wqw2-h65w - NationalSecurityAgency/emissary has an incomplete fix for CVE-2026-35571

### Summary The URL validation regex `^(https?:/)?/.*` added to emissary's `NavAction.java` allows protocol-relative URLs (`//evil.com/...`) and single-slash scheme variants (`http:/evil.com`) to bypass validation, enabling SSRF and open redirect attacks. ### Affected Package - **Ecosystem:** Maven - **Package:** NationalSecurityAgency/emissary - **Affected versions:** < e2078417464b - **Patched versions:** >= e2078417464b ### Severity Medium ### CWE CWE-918 — Server-Side Request Forgery (SSRF) ### Details The fix in `NavAction.java` (line 47) introduces a `VALID_LINK` pattern: ```java Pattern.compile("^(https?:/)?/.*") ``` This regex is intended to restrict navigation links to relative paths and HTTP/HTTPS URLs. However, it has multiple bypass vectors. Protocol-relative URLs (`//evil.com/...`): The group `(https?:/)?` is optional, so the pattern reduces to `//.*` when the group is absent. This matches `//evil.com/steal?c=SESSION`, which browsers resolve to the current page's protocol plus the attacker's host. Single-slash scheme (`http:/evil.com`): The regex group captures `http:/` as a valid match, and browsers normalize `http:/evil.com` to `http://evil.com`, creating an open redirect to the attacker's server. Protocol-relative to cloud metadata (`//169.254.169.254/...`): This enables SSRF to cloud instance metadata endpoints, which is particularly dangerous in AWS/GCP environments where IAM credentials can be retrieved. The pre-fix code had no validation at all, accepting any URL. The fix blocks `javascript:`, `ftp:`, and `data:` URIs, but the protocol-relative and single-slash bypasses remain exploitable. ### PoC ```python """ CVE-2026-35571 - NationalSecurityAgency/emissary SSRF via NavAction The fix in commit e2078417464b adds URL scheme validation using: Pattern.compile("^(https?:/)?/.*") This allows protocol-relative URLs (//evil.com) and single-slash variants (http:/evil.com) to bypass the validation. Tested against: emissary@0d4dc56