CVE-2026-71308 is a high-severity (CVSS 8.1) CWE-639 vulnerability in lemur. O3 Security confirms whether CVE-2026-71308 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Lemur: Unchecked `replaces[]` lets any user silence notifications and hijack auto-rotation for arbitrary certificates
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-71308.
Real-World Exposure
lemurReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
Lemur manages TLS certificate creation. From 0.5.0 until 1.9.3, certificate create, upload, and edit requests accepted replaces[] or replacements identifiers that AssociatedCertificateSchema resolved with fetch_objects without a CertificatePermission check. Assigning those objects to Certificate.replaces invoked an append listener that disabled the victim certificate notifications and marked it as replaced. The victim was then excluded from get_all_pending_reissue, and certificate_rotate could deploy the attacker certificate to endpoints serving the victim. An authenticated non-read-only user could target certificates for which the user had no ownership or role, suppress lifecycle automation, and cause fleet-wide TLS disruption or unauthorized substitution. The fix authorizes every referenced replacement certificate before mutation. This issue is fixed in version 1.9.3.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | lemur | ≥ 0.5.0&&< 1.9.3 | 1.9.3 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for lemur. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update lemur to 1.9.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-71308 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-71308 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-71308. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-71308 in your dependencies?
O3 detects CVE-2026-71308 across PyPI dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.