CVE-2026-70667
PyPI · lemur
Summary
Lemur: SSRF protection in certificate revocation checking bypassable via HTTP redirects and DNS rebinding (incomplete fix for GHSA-54vg-pfh7-jq95)
Advisory details
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:
# 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:
# 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) → verify_string → crl_verify / ocsp_verify. Triggered when verification runs (e.g. the check_revocation task).
PoC
- Generate a cert with
crlDistributionPoints = URI:http://attacker.example/crl. - That host returns
302 Location: http://169.254.169.254/latest/meta-data/...(bypass 1), or use a low-TTL rebinding name (bypass 2). - Upload via
POST /api/1/certificates/uploadas an operator user. - Trigger
lemur certificate check_revocation. - Observe the request reach the internal address (
tcpdump -nni any host 169.254.169.254).
Impact
Blind SSRF from the Lemur host: reach internal services and instance metadata (169.254.169.254 without IMDSv2). Response is parsed as a CRL and discarded — reachability/side-effects, not response exfiltration.
Remediation
allow_redirects=Falseon CRL fetches (or re-validate every redirect hop).- Resolve once, pin the IP, connect to the pinned address; route the OCSP URL through the same check.
- Reject names with any internal A/AAAA record.
References
Related advisories
- CVE-2026-71303 — high · PyPI/lemur
- CVE-2026-70666 — high · PyPI/lemur
- CVE-2026-60091 — high · PyPI/praisonai
- CVE-2026-61430 — high · PyPI/praisonaiagents
- CVE-2026-61429 — high · PyPI/praisonaiagents
- CVE-2026-56676 — high · npm/9router
- CVE-2026-87996 — high · PyPI/open-webui
- CVE-2026-55537 — high · PyPI/PraisonAI
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Sources: CISA KEV (public domain), OSV.dev & GitHub Advisory Database (CC-BY-4.0), FIRST EPSS, NVD/CWE (public domain). Served live from the Stateward advisory database.