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Vulnerabilities

Vulnerability · CVE-2026-44699

LibJWT is a C JSON Web Token Library.

Published May 15, 2026 · catalog updated Jun 17, 2026 · LibJWT is a C

Check if you run it

No confirmed exploitation is on record for CVE-2026-44699. EPSS is 0.35%. Act only if a listed version of LibJWT is a C is installed.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (LibJWT is a C).
  • No version range is stored. A customer cannot check an installed version against this record.
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
Critical9.1
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.35%
Remediation
Advisory link
Affected products
See sources for product scope

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.

No affected version ranges are stored yet. Use the vendor advisory before you decide this record does not apply.

How to fix CVE-2026-44699

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-44699. EPSS is 0.35%. Act only if a listed version of LibJWT is a C is installed.

Which versions are affected?

Affected version ranges are not on this record. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-327: Use of a Broken or Risky Cryptographic Algorithm; CWE-347: Improper Verification of Cryptographic Signature. EPSS 0.35%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. May 15, 2026 · NIST NVD

    Detected

    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 bypas

  2. Jun 17, 2026 · NIST NVD

    Updated

    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 bypas

Sources

  • CVE.orgVulnerability recordCVE-2026-44699

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-44699

    30-day exploitation probability 0.4%

    first.org
  • NIST NVDVulnerability recordCVE-2026-44699

    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

    nvd.nist.gov

References

Freshness

Last verified in this catalog Oct 18, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.