Fast-JWT Improperly Validates iss Claims

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2025-30144: 0.59% estimated exploitation activity in the next 30 days; percentile 48.36 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary The fast-jwt library does not properly validate the iss claim based on the RFC https://datatracker.ietf.org/doc/html/rfc7519#page-9. Details The iss (issuer) claim validation within the fast-jwt library permits an array of strings as a valid iss value. This design flaw enables a potential attack where a malicious actor crafts a JWT with an iss claim structured as ['https://attacker-domain/', 'https://valid-iss']. Due to the permissive validation, the JWT will be deemed valid. Furthermore, if the application relies on external libraries like get-jwks that do not independently validate the iss claim, the attacker can leverage this vulnerability to forge a JWT that will be accepted by the victim application. Essentially, the attacker can insert their own domain into the iss array, alongside the legitimate issuer, and bypass the intended security checks. PoC Take a server running the following code: Now we build a server that will be used to generate the JWT token and send the…

Published by the source

19 Mar 2025, 15:48 UTC

Last modified by the source

20 Mar 2025, 18:58 UTC

Source last checked

26 Oct 2026, 12:36 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-gm45-q3v2-6cf8

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-gm45-q3v2-6cf8

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# Patch Next advisory brief: CVE-2025-30144

Advisory: Fast-JWT Improperly Validates iss Claims
IDs: CVE-2025-30144, GHSA-gm45-q3v2-6cf8
Record: https://patchnext.com/advisories/cve-2025-30144 (revision 2, source checked 26 Oct 2026, 12:36 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: fast-jwt 5.0.6. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm fast-jwt: affected < 5.0.6; fixed in 5.0.6

## Suggested inspection (read-only)
- `npm ls fast-jwt --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on fast-jwt.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-gm45-q3v2-6cf8 (OSV record GHSA-gm45-q3v2-6cf8 lists affected ranges: npm fast-jwt >=0 <5.0.6 (fixed))
- Verified: https://github.com/advisories/GHSA-gm45-q3v2-6cf8 (GitHub-reviewed advisory GHSA-gm45-q3v2-6cf8 lists affected ranges: npm fast-jwt >=0 <5.0.6)

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