Lemonldap::NG::Portal versions from 2.23.0 before 2.23.4 for Perl allow a PKCE bypass for public Relying Parties in "PKCE or secret" mode because checkEndPointAuthenticationCredentials does not verify the client secret.

With oidcRPMetaDataOptionsRequirePKCE set to 2, the authorization endpoint issues a code even when the request carries no code_challenge, and token() admits the exchange as long as a challenge was stored or an authentication method was returned for the caller. checkEndPointAuthenticationCredentials() skips the secret comparison for a Relying Party marked public and still returns the method deduced from the request, so any Basic or form credential satisfies the secret branch. validatePKCEChallenge() then passes, because neither a challenge nor a verifier is present.

An attacker who intercepts an authorization code issued to a public Relying Party can exchange it for the user's access, ID and refresh tokens by replaying the client_id with an arbitrary secret, which is the attack PKCE prevents. Dynamic client registration creates every Relying Party in this mode.
Advisories
Source ID Title
Debian DSA Debian DSA DSA-6520-1 lemonldap-ng security update
Fixes

Solution

Upgrade to Lemonldap-NG-Portal 2.23.4 or later.


Workaround

For deployments that cannot upgrade to 2.23.4, set RequirePKCE to 1 on public Relying Parties so that a code challenge is always required. Relying Parties created through dynamic registration are always in "PKCE or secret" mode, so that endpoint has to be disabled as well.

History

Mon, 28 Sep 2026 20:15:00 +0000

Type Values Removed Values Added
First Time appeared Lemonldap-ng
Lemonldap-ng portal
Vendors & Products Lemonldap-ng
Lemonldap-ng portal

Sat, 26 Sep 2026 23:30:00 +0000

Type Values Removed Values Added
Metrics cvssV3_1

{'score': 9.1, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N'}


Sat, 26 Sep 2026 18:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'poc', 'Technical Impact': 'total'}, 'version': '2.0.3'}


Fri, 25 Sep 2026 03:30:00 +0000

Type Values Removed Values Added
References

Fri, 25 Sep 2026 01:00:00 +0000

Type Values Removed Values Added
Description Lemonldap::NG::Portal versions from 2.23.0 before 2.23.4 for Perl allow a PKCE bypass for public Relying Parties in "PKCE or secret" mode because checkEndPointAuthenticationCredentials does not verify the client secret. With oidcRPMetaDataOptionsRequirePKCE set to 2, the authorization endpoint issues a code even when the request carries no code_challenge, and token() admits the exchange as long as a challenge was stored or an authentication method was returned for the caller. checkEndPointAuthenticationCredentials() skips the secret comparison for a Relying Party marked public and still returns the method deduced from the request, so any Basic or form credential satisfies the secret branch. validatePKCEChallenge() then passes, because neither a challenge nor a verifier is present. An attacker who intercepts an authorization code issued to a public Relying Party can exchange it for the user's access, ID and refresh tokens by replaying the client_id with an arbitrary secret, which is the attack PKCE prevents. Dynamic client registration creates every Relying Party in this mode.
Title Lemonldap::NG::Portal versions from 2.23.0 before 2.23.4 for Perl allow a PKCE bypass for public Relying Parties in "PKCE or secret" mode because checkEndPointAuthenticationCredentials does not verify the client secret
Weaknesses CWE-1390
References

Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: CPANSec

Published:

Updated: 2026-09-26T22:29:08.052Z

Reserved: 2026-09-15T23:43:48.309Z

Link: CVE-2026-92289

cve-icon Vulnrichment

Updated: 2026-09-25T02:10:01.838Z

cve-icon NVD

Status : Deferred

Published: 2026-09-25T01:16:48.943

Modified: 2026-09-26T23:16:38.897

Link: CVE-2026-92289

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-09-28T19:42:57Z

Weaknesses