Authenticated service interruption via catastrophic regex backtracking
Published Apr 9, 2026 · Updated Apr 9, 2026
Regular expression denial of service in Nearform fast-jwt 5.0.0 through 6.2.0 allows remote authenticated users to interrupt services. The verifier applies attacker-controlled JWT claims to unsafe RegExp objects in allowedAud, allowedIss, allowedSub, allowedJti, or allowedNonce, allowing exponential backtracking to monopolize the Node.js event loop. Exploitation requires a valid signed JWT, control of a matched claim, and a configured backtracking-prone expression; defaults and string matchers are unaffected.
Summary
What happened
Regular expression denial of service in Nearform fast-jwt 5.0.0 through 6.2.0 allows remote authenticated users to interrupt services. The verifier applies attacker-controlled JWT claims to unsafe RegExp objects in allowedAud, allowedIss, allowedSub, allowedJti, or allowedNonce, allowing exponential backtracking to monopolize the Node.js event loop. Exploitation requires a valid signed JWT, control of a matched claim, and a configured backtracking-prone expression; defaults and string matchers are unaffected.
The record
- CVE
- CVE-2026-35041
- Published
- Apr 9, 2026
- Updated
- Apr 9, 2026
- Vendor
- Nearform
- Product
- fast-jwt
- Classifications
- CWE-1333, T1499.004
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- Apr 9, 2026CVE publishedPublication date reported by the CVE source.
- Apr 9, 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=>= 5.0.0, < 6.2.1
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
- Upstream fast-jwt ReDoS reproduction procedureproof of concept · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
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Your stack
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