Summary
Lemur: SSRF protection in certificate revocation checking bypassable via HTTP redirects and DNS rebinding (incomplete fix for GHSA-54vg-pfh7-jq95)
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.
Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside. Typical impact: access to internal metadata services, internal APIs, or cloud credentials.
CVE-2026-70667 has a CVSS score of 6.3 (Medium). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.9.3); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Already deployed Kodem?
See it in your environmentNew to Kodem? Get a demo →Remediation advice
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.
Frequently Asked Questions
- What is CVE-2026-70667? CVE-2026-70667 is a medium-severity server-side request forgery (SSRF) vulnerability in lemur (pip), affecting versions < 1.9.3. It is fixed in 1.9.3. Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside.
- How severe is CVE-2026-70667? CVE-2026-70667 has a CVSS score of 6.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of lemur are affected by CVE-2026-70667? lemur (pip) versions < 1.9.3 is affected.
- Is there a fix for CVE-2026-70667? Yes. CVE-2026-70667 is fixed in 1.9.3. Upgrade to this version or later.
- Is CVE-2026-70667 exploitable, and should I be worried? Whether CVE-2026-70667 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-70667 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-70667? Upgrade
lemurto 1.9.3 or later.