CVE-2026-44699
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedLibJWT 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.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceLibJWT 3.0.0-3.3.2 accepts RSA JWKs lacking an alg parameter as verification keys for HMAC algorithms (HS256/HS384/HS512), causing the OpenSSL backend to use a zero-length key. This algorithm-confusion flaw allows attackers to forge valid JWTs without knowing any secret or RSA private key.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- Authentication
- X
- User interaction
- None
- Scope
- X
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/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
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Check the installed libjwt versionQuery your package manager or inspect libjwt library files to determine the version number, then compare it against the affected range 3.0.0 to 3.3.2Affected if The version falls within 3.0.0 through 3.3.2
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Identify if your application uses JWK-based JWT verificationReview application source code or configuration for JWT verification that loads keys from JWK format (typically JSON structures containing kty, n, e fields for RSA keys)Affected if The application uses JWK format for key loading
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Determine if RSA JWKs are used without the alg parameterInspect JWK files or API payloads used for verification and check whether the alg field is present in RSA-type keys (kty= RSA)Affected if RSA JWKs lack the alg parameter field
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Check if HMAC algorithms are used for verification with RSA keysReview JWT verification logic to see if HS256, HS384, or HS512 algorithms are being used with RSA-type keys loaded from JWKsAffected if HMAC algorithms (HS256/HS384/HS512) are used to verify JWTs with RSA keys loaded from JWKs lacking alg
You are affected if libjwt version 3.0.0-3.3.2 is in use AND your application verifies JWTs using HMAC algorithms with RSA JWKs that lack the alg parameter.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scopedUpgrade libjwt to version 3.3.3 or later. Additionally, applications should validate that the JWK alg parameter matches the JWT algorithm before performing verification, especially when using kid lookup callbacks that select verification algorithms from JWT headers.
libjwt 3.3.3
- Identify the current libjwt version in use by checking project dependencies or library version
- Upgrade libjwt to version 3.3.3 or later
- Verify the upgrade was successful by checking the installed version
- Test JWT verification functionality, particularly with RS256-signed tokens using RSA keys from JWKS
- Ensure that HS256/HS384/HS512 tokens are rejected when RSA keys are used for verification (the fix should enforce algorithm matching)
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation2.0 h
- Implementation4.0 h
- Testing6.0 h
- Review / QA2.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-44699 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-44699 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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