Authentication bypass via empty HMAC secret
Published May 13, 2026 · Updated May 13, 2026
Authentication bypass in Nearform fast-jwt before 6.2.4 allows remote attackers to forge JWTs through an empty HMAC secret. In the async key-resolver path, prepareKeyOrSecret converts an empty result to a zero-length Buffer, classifies it for HS256, HS384, and HS512, and verifies attacker-computed HMACs with that key. Exploitation requires a function-typed resolver to return an empty string or Buffer while HMAC is allowed; accepted tokens retain attacker-chosen identity and authorization claims.
Summary
What happened
Authentication bypass in Nearform fast-jwt before 6.2.4 allows remote attackers to forge JWTs through an empty HMAC secret. In the async key-resolver path, prepareKeyOrSecret converts an empty result to a zero-length Buffer, classifies it for HS256, HS384, and HS512, and verifies attacker-computed HMACs with that key. Exploitation requires a function-typed resolver to return an empty string or Buffer while HMAC is allowed; accepted tokens retain attacker-chosen identity and authorization claims.
The record
- CVE
- CVE-2026-44351
- Published
- May 13, 2026
- Updated
- May 13, 2026
- Vendor
- Nearform
- Product
- fast-jwt
- Classifications
- CWE-1391, CWE-326, CWE-287, T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- May 13, 2026CVE publishedPublication date reported by the CVE source.
- May 13, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=< 6.2.4
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- Empty-key HMAC JWT forgery PoCproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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