CVE-2026-52776

### Summary `compliance-trestle` 4.0.3 (latest) ships an `URLSecurityValidator` in `trestle/core/remote/security.py` to block SSRF to loopback / link-local / cloud-metadata endpoints from the HTTPSFetcher and SFTPFetcher remote-fetch paths. The allowlist is incomplete and can be bypassed by four equivalent address representations that resolve to the same blocked host but evade the validator's checks: - IPv4-mapped IPv6 literals (`[::ffff:169.254.169.254]`, `[::ffff:127.0.0.1]`, `[::ffff:10.0.0.1]`) are returned by `socket.getaddrinfo` as `IPv6Address` objects; `IPv6Address in IPv4Network('169.254.0.0/16')` returns `False`, so the `_check_blocked_networks` and `_check_private_networks` predicates do not match. - IPv4 unspecified address `0.0.0.0` is not in `ALWAYS_BLOCKED_NETWORKS` (which covers `127.0.0.0/8` but not `0.0.0.0/8`); on Linux + Docker, `0.0.0.0` routes to local services on any interface, and on dual-stack-mapped sockets it also reaches loopback listeners. A malicious OSCAL profile referencing one of these URLs in `imports[*].href` or `back-matter.resources[*].rlinks[*].href` causes `HTTPSFetcher.__init__` and `_do_fetch` (which both invoke `validator.validate_url`) to pass the URL through to `requests.get`, contacting cloud-metadata services, loopback admin interfaces, or RFC 1918 internal networks (with `TRESTLE_BLOCK_PRIVATE_IPS=true` set) that the validator was specifically designed to block. ### Affected versions `compliance-trestle` (PyPI) versions `<= 4.0.3` are affected. 4.0.3 (released 2026-05-20) is the latest release and the one that introduced `URLSecurityValidator`; prior releases had no SSRF guard at all. ### Privilege required Network-position attacker who can supply or influence an OSCAL artifact (profile / catalog / SSP / component-definition) that compliance-trestle subsequently fetches via `HTTPSFetcher` or `SFTPFetcher`. The most realistic vector is a malicious OSCAL profile whose `imports[*].href` references one of the bypass