# CVE-2026-44699: LibJWT: Algorithm confusion allows JWT forgery with RSA JWK as empty-key HMAC

> Attackers can forge valid JWTs by exploiting algorithm confusion in libjwt, bypassing authentication in applications using RSA JWKs without alg parameters.

- **Severity:** Critical 9.1 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 15 May 2026
- **Updated:** 15 May 2026
- **Also known as:** DEBIAN-CVE-2026-44699, GHSA-q843-6q5f-w55g, UBUNTU-CVE-2026-44699

## What is CVE-2026-44699?

CVE-2026-44699 is a critical authentication bypass vulnerability in benmcollins libjwt, published on 15 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

LibJWT is a C JSON Web Token Library. From 3.0.0 to 3.3.2, libjwt accepts an RSA JWK that does not contain an alg parameter as the verification key for an HS256/HS384/HS512 token. In the OpenSSL backend, this causes HMAC verification to run with a zero-length key, so an attacker can forge a valid JWT without knowing any secret or RSA private key. This is an algorithm-confusion authentication bypass. It affects applications that load RSA keys from JWKS where alg is omitted, which is valid JWK syntax and common in real deployments, and then choose the verification algorithm from the JWT header, for example in a kid lookup callback. This vulnerability is fixed in 3.3.3.

Weakness: CWE-347 (Improper Verification of Cryptographic Signature), CWE-327 (Use of a Broken or Risky Cryptographic Algorithm)

## Which versions are affected by CVE-2026-44699?


## How do I fix CVE-2026-44699?

Upgrade to a fixed version.

## Is CVE-2026-44699 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-44699 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-44699 and fix it if it is affected.

What it is: CVE-2026-44699 is a critical authentication bypass vulnerability in benmcollins libjwt, published on 15 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-44699 exists.

Affected product: benmcollins libjwt. 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-2026-44699/ (Markdown: https://insights.sbomify.com/CVE-2026-44699/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-44699
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-44699
- OSV: https://osv.dev/vulnerability/CVE-2026-44699

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-44699/
Summaries are generated and may contain mistakes; the official description above is the record.