Lemur: Incomplete fix for GHSA-v2wp-frmc-5q3v -- ACME authority update endpoint allows non-admin to replace acme_url with internal IP, bypassing allowlist

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

7.7 · CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N

EPSS

• CVE-2026-71303: 0.28% estimated exploitation activity in the next 30 days; percentile 20.21 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary The fix for GHSA-v2wp-frmc-5q3v added validateacmeurl() to reject acmeurl values not in ACMEDIRECTORYHOSTALLOWLIST, but the validation is only called at authority creation time (POST). The authority update endpoint (PUT /api/1/authorities/<id) accepts and stores arbitrary options -- including a modified acmeurl -- without invoking the allowlist check. Any user with an authority role (granted by an admin to allow issuing certificates via that authority) can therefore overwrite the stored acmeurl with an internal IP or IMDS endpoint. The next certificate issuance via that authority causes Lemur's backend to fetch the attacker-controlled URL, achieving SSRF. Details Where the fix lives (POST path -- protected): lemur/plugins/lemuracme/plugin.py lines 333-337 (ACMEIssuerPlugin.createauthority): validateacmeurl at line 35: Where the gap is (PUT path -- unprotected): lemur/authorities/views.py lines 405-424 (Authorities.put): lemur/authorities/service.py lines 28-46 (update): Where…

Published by the source

18 Aug 2026, 20:51 UTC

Last modified by the source

18 Aug 2026, 20:51 UTC

Source last checked

26 Oct 2026, 13:50 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-v5rc-cpwc-cfpr

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# Patch Next advisory brief: CVE-2026-71303

Advisory: Lemur: Incomplete fix for GHSA-v2wp-frmc-5q3v -- ACME authority update endpoint allows non-admin to replace `acme_url` with internal IP, bypassing allowlist
IDs: CVE-2026-71303, GHSA-v5rc-cpwc-cfpr
Record: https://patchnext.com/advisories/cve-2026-71303 (revision 1, source checked 26 Oct 2026, 13:50 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: lemur 1.9.3. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI lemur: affected <= 1.9.2; fixed in 1.9.3

## Suggested inspection (read-only)
- `python -m pip show lemur`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on lemur.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-v5rc-cpwc-cfpr (GitHub-reviewed advisory GHSA-v5rc-cpwc-cfpr lists affected ranges: PyPI lemur >=0 <=1.9.2)

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