UBUNTU-CVE-2026-44699 (CVE-2026-44699)
Vulnerability from osv_ubuntu – Published: 2026-05-15 17:16 – Updated: 2026-05-15 17:16 – Source website
VLAI
Details
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.
Severity
N/A (UNKNOWN)
References
{
"affected": [
{
"ecosystem_specific": {
"binaries": [
{
"binary_name": "libjwt0",
"binary_version": "1.9.0-1build1"
}
]
},
"package": {
"ecosystem": "Ubuntu:18.04:LTS",
"name": "libjwt",
"purl": "pkg:deb/ubuntu/libjwt@1.9.0-1build1?arch=source\u0026distro=bionic"
},
"ranges": [
{
"events": [
{
"introduced": "0"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"1.8.0+dfsg-1",
"1.8.0+dfsg-2",
"1.9.0-1",
"1.9.0-1build1"
]
},
{
"ecosystem_specific": {
"binaries": [
{
"binary_name": "libjwt-gnutls0",
"binary_version": "1.10.2-1"
},
{
"binary_name": "libjwt0",
"binary_version": "1.10.2-1"
}
]
},
"package": {
"ecosystem": "Ubuntu:20.04:LTS",
"name": "libjwt",
"purl": "pkg:deb/ubuntu/libjwt@1.10.2-1?arch=source\u0026distro=focal"
},
"ranges": [
{
"events": [
{
"introduced": "0"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"1.10.2-1"
]
},
{
"ecosystem_specific": {
"binaries": [
{
"binary_name": "libjwt-gnutls0",
"binary_version": "1.10.2-1build1"
},
{
"binary_name": "libjwt0",
"binary_version": "1.10.2-1build1"
}
]
},
"package": {
"ecosystem": "Ubuntu:22.04:LTS",
"name": "libjwt",
"purl": "pkg:deb/ubuntu/libjwt@1.10.2-1build1?arch=source\u0026distro=jammy"
},
"ranges": [
{
"events": [
{
"introduced": "0"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"1.10.2-1",
"1.10.2-1build1"
]
},
{
"ecosystem_specific": {
"binaries": [
{
"binary_name": "libjwt-gnutls2",
"binary_version": "1.17.0-2build2"
},
{
"binary_name": "libjwt2",
"binary_version": "1.17.0-2build2"
}
]
},
"package": {
"ecosystem": "Ubuntu:24.04:LTS",
"name": "libjwt",
"purl": "pkg:deb/ubuntu/libjwt@1.17.0-2build2?arch=source\u0026distro=noble"
},
"ranges": [
{
"events": [
{
"introduced": "0"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"1.10.2-1build1",
"1.17.0-2",
"1.17.0-2build1",
"1.17.0-2build2"
]
},
{
"ecosystem_specific": {
"binaries": [
{
"binary_name": "libjwt-gnutls2",
"binary_version": "1.17.2-1"
},
{
"binary_name": "libjwt2",
"binary_version": "1.17.2-1"
}
]
},
"package": {
"ecosystem": "Ubuntu:25.10",
"name": "libjwt",
"purl": "pkg:deb/ubuntu/libjwt@1.17.2-1?arch=source\u0026distro=questing"
},
"ranges": [
{
"events": [
{
"introduced": "0"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"1.17.2-1"
]
},
{
"ecosystem_specific": {
"binaries": [
{
"binary_name": "libjwt-gnutls2",
"binary_version": "1.17.2-1build1"
},
{
"binary_name": "libjwt2",
"binary_version": "1.17.2-1build1"
}
]
},
"package": {
"ecosystem": "Ubuntu:26.04:LTS",
"name": "libjwt",
"purl": "pkg:deb/ubuntu/libjwt@1.17.2-1build1?arch=source\u0026distro=resolute"
},
"ranges": [
{
"events": [
{
"introduced": "0"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"1.17.2-1",
"1.17.2-1build1"
]
},
{
"ecosystem_specific": {
"binaries": [
{
"binary_name": "jwt-tools",
"binary_version": "3.2.3-1"
},
{
"binary_name": "libjwt14",
"binary_version": "3.2.3-1"
}
]
},
"package": {
"ecosystem": "Ubuntu:26.04:LTS",
"name": "libjwt3",
"purl": "pkg:deb/ubuntu/libjwt3@3.2.3-1?arch=source\u0026distro=resolute"
},
"ranges": [
{
"events": [
{
"introduced": "0"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"3.2.2-1",
"3.2.3-1"
]
}
],
"aliases": [],
"details": "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.",
"id": "UBUNTU-CVE-2026-44699",
"modified": "2026-05-15T17:16:00Z",
"published": "2026-05-15T17:16:00Z",
"references": [
{
"type": "REPORT",
"url": "https://ubuntu.com/security/CVE-2026-44699"
},
{
"type": "REPORT",
"url": "https://www.cve.org/CVERecord?id=CVE-2026-44699"
},
{
"type": "REPORT",
"url": "https://github.com/benmcollins/libjwt/security/advisories/GHSA-q843-6q5f-w55g"
}
],
"related": [],
"schema_version": "1.7.0",
"severity": [
{
"score": "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",
"type": "CVSS_V4"
},
{
"score": "medium",
"type": "Ubuntu"
}
],
"upstream": [
"CVE-2026-44699"
]
}
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vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
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The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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