CVE-2026-54689

## Summary `mcp-searxng` has a hardened-mode URL-reading feature intended to prevent `web_url_read` from reaching private or internal network resources. PR #79 appears to address one SSRF class: hostnames that resolve to private or internal addresses under hardened mode. I tested PR #79 locally and confirmed that it blocks the DNS-resolves-to-loopback case. However, several other hardened-mode SSRF bypasses still appear to remain: 1. Redirects from an allowed first-hop URL to a loopback/internal URL are followed without re-validating the redirect target. 2. `0.0.0.0` is not treated as an internal/special address. 3. IPv4-mapped IPv6 literals can bypass private-address checks after URL canonicalization. With hardened mode enabled and private URLs not explicitly allowed, `web_url_read` was still able to fetch and return content from a local loopback sentinel service in all three cases. ## Tested configuration ```bash MCP_HTTP_HARDEN=true MCP_HTTP_ALLOW_PRIVATE_URLS unset ``` The MCP server was driven over stdio. The test target was a harmless internal sentinel HTTP service bound to: ```text 127.0.0.1:6789 ``` The sentinel response contained: ```text INTERNAL_SECRET_DATA__mcp_searxng_ssrf_path2 ``` ## Relationship to PR #79 I tested PR #79 locally: - PR: `fix(url-reader): block DNS-rebinding SSRF via socket-level lookup guard (CWE-918) #79` - PR commit tested: `e55d28e7be6786a71cd7a0eaf13d3ec9d0b734d4` - Base issue class: CWE-918 / SSRF in `web_url_read` - Hardened mode: enabled Observed results: ```text Case Result on PR #79 ------------------------------------------------------------- DNS hostname resolving to 127.0.0.1 blocked 0.0.0.0 BYPASS [::ffff:127.0.0.1] BYPASS redirect from non-private IP to 127.0.0.1 BYPASS ``` So PR #79 is a useful fix, but it does not fully close hardened-mode internal URL access. ## Root cause ### 1. Redir