Summary
Lemur Privilege Escalation: Non-admin role members can rewrite role membership via PUT /api/1/roles/<id>
The PUT /api/1/roles/<id> handler in lemur/roles/views.py gates only on RoleMemberPermission(role_id).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 @admin_permission.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:
permission = RoleMemberPermission(role_id)
if permission.can():
return service.update(
role_id, data["name"], data.get("description"), data.get("users")
)
return dict(message="You are not authorized to modify this role."), 403
@admin_permission.require(http_exception=403)
def delete(self, role_id):
...
lemur/auth/permissions.py:56:
class RoleMemberPermission(Permission):
def __init__(self, role_id):
needs = [RoleNeed("admin"), RoleMemberNeed(role_id)]
super().__init__(*needs)
flask_principal.Permission.allows() is OR-semantic across needs, so RoleMemberPermission(role_id).can() returns True if the caller is either an admin or a member of role_id. The PUT handler treats membership-of-self as sufficient to mutate the role; DELETE does not.
Affected Endpoints
| Method | Path | Source |
|---|---|---|
| PUT | /api/1/roles/<id> |
lemur/roles/views.py:298 |
Steps to Reproduce
Set up Lemur with default configuration. Create an admin user
admin, and two non-admin usersaliceandbob. Addaliceto the built-inoperatorrole; leavebobwith no roles or withread-onlyonly.Authenticate as
aliceand capture the JWT:curl -X POST https://lemur.local/api/1/auth/login \ -H "Content-Type: application/json" \ -d '{"username":"alice","password":"<alice_pw>"}'Confirm the initial state -
bobis not a member ofoperator:curl https://lemur.local/api/1/roles?filter=name;operator \ -H "Authorization: Bearer <admin_jwt>" # observe: alice present in users list, bob absentAs
alice, send a PUT that injectsbobinto theoperatorrole:curl -X PUT https://lemur.local/api/1/roles/<operator_role_id> \ -H "Authorization: Bearer <alice_jwt>" \ -H "Content-Type: application/json" \ -d '{ "name": "operator", "description": "modified by alice", "users": [{"id": <alice_id>}, {"id": <bob_id>}] }' # observe: HTTP 200Confirm
bobis now a member ofoperator:curl https://lemur.local/api/1/roles?filter=name;operator \ -H "Authorization: Bearer <admin_jwt>" # observe: bob now present in users list
Step 4 succeeds despite alice not being an admin. The same handler also accepts a name field; substituting "name": "operator_v2" in step 4 renames the role, demonstrating the second variant of the bug.
Impact
A user who is a member of role X can:
- Add other users to role X, granting them whatever certificate/authority access role X confers. In installs that delegate certificate or authority ownership to non-admin roles, this promotes arbitrary users to peer of every other role member.
- Remove other users from role X, denying their access (availability / governance impact).
- Rename role X to an arbitrary string.
The "rename to admin" path is blocked by theunique=Trueconstraint onRole.nameand by strict equality inUser.is_admin, so direct self-promotion to admin via rename is not possible on default installs. The principal exploitation surface is membership rewriting and lateral promotion of colluders within roles the attacker already belongs to.
The application does not correctly enforce access controls, allowing a principal to access resources or operations beyond their granted permissions. Typical impact: unauthorized data access or execution of privileged operations.
CVE-2026-55163 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 (1.9.2); 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.
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Add @admin_permission.require(http_exception=403) to Roles.put, mirroring the existing decorator on Roles.delete:
@admin_permission.require(http_exception=403)
def put(self, role_id, data=None):
...
If selective delegation is intended (role owners managing their own roles), that capability should be modeled with a dedicated permission class whose Needs reflect role ownership rather than membership, and the name field should be excluded from the mutable schema on that delegated path.
Frequently Asked Questions
- What is CVE-2026-55163? CVE-2026-55163 is a medium-severity incorrect authorization vulnerability in lemur (pip), affecting versions <= 1.9.1. It is fixed in 1.9.2. The application does not correctly enforce access controls, allowing a principal to access resources or operations beyond their granted permissions.
- How severe is CVE-2026-55163? CVE-2026-55163 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-2026-55163? lemur (pip) versions <= 1.9.1 is affected.
- Is there a fix for CVE-2026-55163? Yes. CVE-2026-55163 is fixed in 1.9.2. Upgrade to this version or later.
- Is CVE-2026-55163 exploitable, and should I be worried? Whether CVE-2026-55163 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-2026-55163 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-2026-55163? Upgrade
lemurto 1.9.2 or later.