JWT Algorithm Confusion in json-web-token library

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Summary

CVECVE-2023-48238
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2023-11-17 22:15:07 UTC
Updated2026-06-09 00:16:44 UTC
Descriptionjoaquimserafim/json-web-token is a javascript library use to interact with JSON Web Tokens (JWT) which are a compact URL-safe means of representing claims to be transferred between two parties. Versions prior to 4.0.0 are vulnerable to a JWT algorithm confusion attack. On line 86 of the 'index.js' file, the algorithm to use for verifying the signature of the JWT token is taken from the JWT token, which at that point is still unverified and thus shouldn't be trusted. To exploit this vulnerability, an attacker needs to craft a malicious JWT token containing the HS256 algorithm, signed with the public RSA key of the victim application. This attack will only work against this library is the RS256 algorithm is in use, however it is a best practice to use that algorithm. Version 4.0.0 fixes the issue.

Risk And Classification

Primary CVSS: v3.1 7.5 HIGH from [email protected]

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

EPSS: 0.003070000 probability, percentile 0.224400000 (date 2026-07-05)

Problem Types: CWE-345 | CWE-345 CWE-345: Insufficient Verification of Data Authenticity

VersionSourceTypeScoreSeverityVector
3.1[email protected]Primary7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
3.1[email protected]Secondary7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
3.1CNADECLARED7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Application Joaquimserafim Json Web Token All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Joaquimserafim Json-web-token affected < 4.0.0 Not specified

References

ReferenceSourceLinkTags
github.com/joaquimserafim/json-web-token/commit/b6e56b1346f48432d29133c7... [email protected] github.com
JWT Algorithm Confusion · Advisory · joaquimserafim/json-web-token · GitHub af854a3a-2127-422b-91ae-364da2661108 github.com Exploit, Vendor Advisory
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Legacy QID Mappings

  • 996008 NodeJs (Npm) Security Update for json-web-token (GHSA-4xw9-cx39-r355)
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