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liboauth2 CVE-2026-54431

| EUVDEUVD-2026-41277 MEDIUM
Improperly Implemented Security Check for Standard (CWE-358)
2026-07-02 CERT-PL GHSA-3pf6-g4x4-jm46
Information Disclosure Liboauth2
5.1
CVSS 4.0 · Vendor: CERT-PL
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Severity by source

Vendor (CERT-PL) PRIMARY
5.1 MEDIUM
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
vuln.today AI
6.5 MEDIUM

Network vector because DPoP proofs arrive over HTTP; PR:N since proof submission requires no prior authentication; C:L and I:L reflect private key disclosure risk and DPoP binding bypass respectively.

3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N

Primary rating from Vendor (CERT-PL).

CVSS VectorVendor: CERT-PL

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Attack Vector
Local
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
X

Lifecycle Timeline

2
Patch available
Jul 02, 2026 - 12:02 EUVD
Analysis Generated
Jul 02, 2026 - 11:16 vuln.today

DescriptionCVE.org

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

AnalysisAI

DPoP (Demonstrating Proof-of-Possession) proof verification in OpenIDC's liboauth2 C library incorrectly accepts malformed proofs that embed private Elliptic Curve (EC) key material in the JWK header, directly violating RFC 9449 §4.3 step 7. The oauth2_token_verify() function returns success instead of rejecting such proofs, subverting DPoP's core token-binding security guarantee and enabling information disclosure of private key material. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
Craft DPoP proof JWT with EC private key in JWK header
Delivery
Submit proof to liboauth2-protected API endpoint
Exploit
oauth2_token_verify() omits RFC 9449 §4.3 step 7 validation
Execution
Malformed proof accepted as valid
Persist
DPoP token binding bypassed
Impact
Private EC key material potentially logged or processed server-side
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Vulnerability AssessmentAI

Exploitation Exploitation requires that the target server uses liboauth2 prior to version 2.3.0 AND has DPoP proof verification enabled - servers not using DPoP are entirely unaffected. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The assigned CVSS 4.0 score of 5.1 (Medium) with 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 presents a notable inconsistency: AV:L (Local attack vector) conflicts with the nature of liboauth2 as a server-side network-facing library that processes DPoP proofs delivered over HTTP. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario An attacker targeting a resource server or authorization server built on liboauth2 constructs a DPoP proof JWT in which the `jwk` header parameter contains a complete EC private key (rather than only the public key component). The attacker submits this crafted proof alongside an access token to a DPoP-protected endpoint. …
Remediation Upgrade liboauth2 to version 2.3.0 or later, which contains the fix per commit c0b57152ed6a0af33aeb04a60bd7f5bff5ab8800 (https://github.com/OpenIDC/liboauth2/commit/c0b57152ed6a0af33aeb04a60bd7f5bff5ab8800). … Detailed patch versions, workarounds, and compensating controls in full report.
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CVE-2026-54431 vulnerability details – vuln.today
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