vulnerability / NVI-00015220 / Revision 1
Lemur: SSRF protection in certificate revocation checking bypassable via HTTP redirects and DNS rebinding (incomplete fix for GHSA-54vg-pfh7-jq95)
GitHub lists this reviewed advisory for lemur. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
6.3 medium
GitHub source severity; exploitability and local consequence require separate evidence.
As of · GitHub Advisory Database
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
lemur
source listed< 1.9.3
## 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 ins
03 / Response
What to do next
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. GitHub Advisory Database
A fixed release is not deployment evidence.
Check current vendor support and compatibility. After making a change, verify the deployed build and relevant runtime conditions. Keep the evidence, owner and time. An updated lockfile alone does not prove what is running.
04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
05 / Provenance
Sources you can inspect
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- GHSA-f3qq-49m6-rw8f ↗
GitHub Advisory Database · vendor advisory
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Public revision history
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- Revision 1 ·
First indexed by Null; source disclosure date is shown separately.