# CVE-2026-54431: Improper Data Validation in liboauth2

> Attackers can bypass DPoP proof validation by embedding private keys in the JWK header, allowing unauthorized token usage.

- **Severity:** Medium 5.1 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 2 Jul 2026
- **Updated:** 2 Jul 2026
- **Also known as:** AZL-91682, DEBIAN-CVE-2026-54431, GHSA-3pf6-g4x4-jm46, UBUNTU-CVE-2026-54431

## What is CVE-2026-54431?

CVE-2026-54431 is a medium-severity vulnerability in OpenIDC liboauth2, published on 2 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### 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

Weakness: CWE-358 (Improperly Implemented Security Check for Standard)

## Which versions are affected by CVE-2026-54431?


## How do I fix CVE-2026-54431?

Upgrade to a fixed version.

## Is CVE-2026-54431 being exploited?

There is no known exploitation of CVE-2026-54431 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-54431 and fix it if it is affected.

What it is: CVE-2026-54431 is a medium-severity vulnerability in OpenIDC liboauth2, published on 2 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-54431 in the wild and no public exploit code.

Affected product: OpenIDC liboauth2. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-54431/ (Markdown: https://insights.sbomify.com/CVE-2026-54431/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-54431
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-54431
- OSV: https://osv.dev/vulnerability/CVE-2026-54431

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-54431/
Summaries are generated and may contain mistakes; the official description above is the record.