Vulnerability · Published Jul 2, 2026 · Assigned by CERT-PL

CVE-2026-54431Improper Data Validation in liboauth2

Medium 5.1

In plain English

A medium-severity security flaw in liboauth2 from OpenIDC. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 7% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 4.0)5.1Medium

Exploit odds (30 days)0.2%top 92.6% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

In liboauth2 the Demonstrating Proof-of-Possession (DPoP) verifier accepts a proof whose JSON Web Key (jwk) header contains private key material. RFC 9449 section 4.3 step 7 requires the verifier to reject such a proof but oauth2_token_verify() function returns success for a malformed DPoP proof that embeds the private Elliptic Curve (EC) key in the header. This issue was fixed in version 2.3.0

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Debian:12	liboauth2	no fix listed	DEBIAN-CVE-2026-54431
Debian:13	liboauth2	no fix listed	DEBIAN-CVE-2026-54431
Debian:14	liboauth2	2.3.0-1	DEBIAN-CVE-2026-54431
Ubuntu:22.04:LTS	liboauth2	no fix listed	UBUNTU-CVE-2026-54431
Ubuntu:24.04:LTS	liboauth2	no fix listed	UBUNTU-CVE-2026-54431
Ubuntu:25.10	liboauth2	no fix listed	UBUNTU-CVE-2026-54431
Ubuntu:26.04:LTS	liboauth2	no fix listed	UBUNTU-CVE-2026-54431
Ubuntu:26.10	liboauth2	no fix listed	UBUNTU-CVE-2026-54431

Affected products (as reported)

Vendor	Product	Versions
OpenIDC	liboauth2	0 – before 2.3.0

Weakness: CWE-358 · Vector: CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N

References

https://cert.pl/en/posts/2026/07/CVE-2026-54430 third-party-advisory
https://github.com/OpenIDC/liboauth2 product
https://github.com/OpenIDC/liboauth2/commit/c0b57152ed6a0af33aeb04a60bd7f5bff5ab8800 issue-tracking