CVE-2026-55163 in Lemur
Summary
by MITRE • 08/18/2026
Lemur manages TLS certificate creation. Prior to 1.9.2, PUT /api/1/roles/ in lemur/roles/views.py:298 authorized updates with RoleMemberPermission(role_id), which allowed either an administrator or any existing member of the target role. The handler passed data["users"] and data["name"] to service.update, allowing a non-admin member to add or remove other users and rename the role. This enabled lateral privilege grants within roles that control certificate and authority access and could deny access by removing legitimate members. The DELETE handler already required admin_permission, confirming that the weaker PUT authorization was inconsistent. The fix applies the same administrator-only requirement to the PUT handler. This issue is fixed in version 1.9.2.
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Analysis
by VulDB Data Team • 08/18/2026
The vulnerability identified in Lemur prior to version 1.9.2 represents a critical Broken Access Control flaw within its role management API, specifically affecting the endpoint used for updating role configurations. Lemur serves as a central service for managing TLS certificates and authorities, making accurate access control over roles essential for maintaining security boundaries between different teams or services. The core technical issue resides in the PUT handler located at lemurs/roles/views.py on line 298, which was designed to allow modifications to role attributes such as name and associated user memberships. However, the authorization logic governing this endpoint relied exclusively on RoleMemberPermission based on the target role identifier. This permission model incorrectly assumed that any existing member of a role possessed sufficient privileges to alter its configuration, failing to distinguish between read-only membership rights and administrative control over the role itself.
This architectural oversight allowed authenticated users who were merely members of a specific role to execute unauthorized modifications without requiring administrator-level credentials. By exploiting this inconsistency in authorization checks, an attacker could manipulate the data["users"] field to add new individuals as members or remove existing legitimate members from the role. Furthermore, the handler permitted changes to the data["name" ] field, allowing for the renaming of roles which can disrupt operational workflows and audit trails. The ability to arbitrarily modify membership lists effectively grants lateral privilege escalation within the context of that specific role. Since Lemur roles dictate access permissions for sensitive assets like TLS certificates and certificate authorities, gaining control over a role's composition allows an attacker to grant themselves or others elevated privileges they were not originally intended to hold.
The operational impact of this vulnerability is severe due to the centralization of trust in Lemur’s role-based access model. An adversary who successfully exploits this flaw can escalate their privileges by adding themselves as a member to high-privilege roles, thereby gaining unauthorized access to critical certificate management functions. This could lead to the issuance of fraudulent certificates for malicious domains or the exfiltration of private keys associated with sensitive services. Additionally, the capability to remove legitimate members introduces a denial-of-service vector against internal operations by locking out authorized personnel from managing their required certificates. The inconsistency was further highlighted by the fact that the DELETE handler for roles already enforced an administrator-only permission check, indicating that the weaker authorization on the PUT endpoint was likely an oversight rather than a deliberate design choice.
To mitigate this risk and align with industry standards such as CWE-269 which addresses Improper Privilege Management, organizations must ensure that administrative actions like modifying role memberships are strictly reserved for users with explicit administrator privileges. The vulnerability has been addressed in Lemur version 1.9.2 by applying the same stringent administrator-only requirement to the PUT handler, thereby correcting the authorization logic and preventing non-admin members from altering role configurations. Until an upgrade is performed, administrators should monitor API logs for unusual patterns of role modification initiated by standard user accounts and restrict direct database access to roles as a compensating control. This incident underscores the importance of implementing principle of least privilege across all administrative endpoints and conducting regular audits of permission models in identity management systems.