CVE-2026-70667

## Summary The SSRF mitigation added for GHSA-54vg-pfh7-jq95 (`_validate_revocation_url()` in `lemur /certificates/verify.py`) can be bypassed. An operator-role user who uploads a certificate with attacker-controlled CRL/OCSP extensions can still make Lemur reach internal destinations (RFC1918, loopback, link-local 169.254.169.254) during verification. ## Affected version Tested against `main` (the commit that introduced `_validate_revocation_url`). The 1.9.2 release predates that guard and is vulnerable to the original SSRF (GHSA-54vg-pfh7-jq95) directly; this bypass applies to the unreleased mitigation in `main`. Please map the affected range to whichever release will first contain `_validate_revocation_url`. ## Bypass 1 — HTTP redirect (deterministic) The guard validates only the URL in the certificate; the CRL fetch then follows redirects without re-validating the target: ```python # lemur/certificates/verify.py:174 response = requests.get(point, timeout=(3.05, 6)) ``` The attacker hosts the CRL URL on a public host they control (passes the guard); that host returns `302 Location: http://169.254.169.254/...`. `requests` follows it to the internal target the guard never inspected. ## Bypass 2 — DNS rebinding / TOCTOU (probabilistic) The guard resolves once during validation; the fetch re-resolves independently: ```python # lemur/certificates/verify.py:51 addr = ipaddress.ip_address(socket.gethostbyname(hostname)) ``` A low-TTL attacker name that answers a public IP at check time and an internal IP at fetch time passes the guard but is fetched internally. Same gap affects the OCSP path (`openssl ocsp -url <url>`, verify.py:90-99). ## Relationship to GHSA-54vg-pfh7-jq95 Incomplete-fix of that mitigation, not a duplicate. Bypass 1 is not mentioned there; bypass 2 is the rebinding gap that advisory's remediation text anticipated ("pins the resolved IP") but the code does not implement. ## Affected endpoint `POST /api/1/certificates/upload` (operator role) →