Lemur Privilege Escalation: Non-admin role members can rewrite role membership via PUT /api/1/roles/

Exploitation

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

CVSS

6.3 · CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L

EPSS

• CVE-2026-55163: 0.22% estimated exploitation activity in the next 30 days; percentile 12.10 (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 PUT /api/1/roles/<id handler in lemur/roles/views.py gates only on RoleMemberPermission(roleid).can(), which is satisfied for any user who is already a member of the target role. The handler then passes data["users"] and data["name"] directly to service.update(), permitting any role member to rewrite that role's membership list and name. The companion DELETE handler on the same resource is correctly gated by @adminpermission.require; the asymmetry between PUT and DELETE on identical resources indicates an authorization oversight rather than a deliberate design choice. Root Cause lemur/roles/views.py:298: lemur/auth/permissions.py:56: flaskprincipal.Permission.allows() is OR-semantic across needs, so RoleMemberPermission(roleid).can() returns True if the caller is either an admin or a member of roleid. The PUT handler treats membership-of-self as sufficient to mutate the role; DELETE does not. Affected Endpoints | Method | Path | Source | |---|---|---| | PUT |…

Published by the source

25 Jun 2026, 22:01 UTC

Last modified by the source

13 Jul 2026, 16:42 UTC

Source last checked

26 Oct 2026, 13:46 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-x3vf-mgxj-7785

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-x3vf-mgxj-7785

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# Patch Next advisory brief: CVE-2026-55163

Advisory: Lemur Privilege Escalation: Non-admin role members can rewrite role membership via PUT /api/1/roles/
IDs: CVE-2026-55163, GHSA-x3vf-mgxj-7785
Record: https://patchnext.com/advisories/cve-2026-55163 (revision 2, source checked 26 Oct 2026, 13:46 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: lemur 1.9.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI lemur: affected <= 1.9.1; fixed in 1.9.2

## 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://osv.dev/vulnerability/GHSA-x3vf-mgxj-7785 (OSV record GHSA-x3vf-mgxj-7785 lists affected ranges: PyPI lemur >=0 <1.9.2 (fixed))
- Verified: https://github.com/advisories/GHSA-x3vf-mgxj-7785 (GitHub-reviewed advisory GHSA-x3vf-mgxj-7785 lists affected ranges: PyPI lemur >=0 <=1.9.1)

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