mcp-searxng is a Model Context Protocol server that gives AI assistants web search and URL-reading capabilities through SearXNG. Prior to 1.2.0, the web_url_read URL policy in src/url-reader.ts can be bypassed while MCP_HTTP_HARDEN is enabled and MCP_HTTP_ALLOW_PRIVATE_URLS is not enabled because redirect targets are not revalidated, 0.0.0.0 is not classified as an internal address, and IPv4-mapped IPv6 literals canonicalized to hexadecimal form are not recognized. These inputs allow an attacker-influenced tool call to make the MCP server fetch loopback or internal HTTP resources and return content from local services, private APIs, service-mesh endpoints, or cloud metadata endpoints. The separate hostname-to-private-address case addressed by the earlier partial fix is not part of these residual bypasses. This issue is fixed in version 1.2.0.

Affected: npm: mcp-searxng

## 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` - Harden…