Bug 2540976

Summary:	CVE-2026-92289 lemonldap-ng: lemonldap-ng: Authentication bypass via improper PKCE verification [fedora-all]
Product:	[Fedora] Fedora	Reporter:	Vladimir Vasilev <vvasilev>
Component:	lemonldap-ng	Assignee:	Xavier Bachelot <xavier>
Status:	ON_QA ---	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	rawhide	CC:	xavier
Target Milestone:	---	Keywords:	Security, SecurityTracking
Target Release:	---
Hardware:	Unspecified
OS:	Unspecified
Whiteboard:	{"flaws": ["6c06cc95-24d3-448a-b318-62d62d786043"]}
Fixed In Version:		Doc Type:	---
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:		Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:
Bug Blocks:	2540882

Description Vladimir Vasilev 2026-09-25 07:34:32 UTC

Disclaimer: Community trackers are created by Red Hat Product Security team on a best effort basis. Package maintainers are required to ascertain if the flaw indeed affects their package, before starting the update process.

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.

Comment 1 Fedora Update System 2026-09-25 08:14:16 UTC

FEDORA-2026-76a3490aa6 (lemonldap-ng-2.23.4-1.fc45) has been submitted as an update to Fedora 45.
https://bodhi.fedoraproject.org/updates/FEDORA-2026-76a3490aa6

Comment 2 Fedora Update System 2026-09-25 08:14:25 UTC

FEDORA-2026-827241e2de (lemonldap-ng-2.23.4-1.fc44) has been submitted as an update to Fedora 44.
https://bodhi.fedoraproject.org/updates/FEDORA-2026-827241e2de

Comment 3 Fedora Update System 2026-09-25 08:14:33 UTC

FEDORA-2026-33dcab55b4 (lemonldap-ng-2.23.4-1.fc43) has been submitted as an update to Fedora 43.
https://bodhi.fedoraproject.org/updates/FEDORA-2026-33dcab55b4

Comment 4 Fedora Update System 2026-09-26 01:47:47 UTC

FEDORA-2026-76a3490aa6 has been pushed to the Fedora 45 testing repository.
Soon you'll be able to install the update with the following command:
`sudo dnf upgrade --enablerepo=updates-testing --refresh --advisory=FEDORA-2026-76a3490aa6`
You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2026-76a3490aa6

See also https://fedoraproject.org/wiki/QA:Updates_Testing for more information on how to test updates.

Comment 5 Fedora Update System 2026-09-26 02:04:12 UTC

FEDORA-2026-827241e2de has been pushed to the Fedora 44 testing repository.
Soon you'll be able to install the update with the following command:
`sudo dnf upgrade --enablerepo=updates-testing --refresh --advisory=FEDORA-2026-827241e2de`
You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2026-827241e2de

See also https://fedoraproject.org/wiki/QA:Updates_Testing for more information on how to test updates.

Comment 6 Fedora Update System 2026-09-26 02:27:29 UTC

FEDORA-2026-33dcab55b4 has been pushed to the Fedora 43 testing repository.
Soon you'll be able to install the update with the following command:
`sudo dnf upgrade --enablerepo=updates-testing --refresh --advisory=FEDORA-2026-33dcab55b4`
You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2026-33dcab55b4

See also https://fedoraproject.org/wiki/QA:Updates_Testing for more information on how to test updates.