How to Fix CVE-2026-35039: fast-jwt (Bundle Sibling)

*By Sai Kiran Pandrala*

Last verified: 2026-05-25

CVE-2026-35039 is a sibling vulnerability in the same Nearform fast-jwt advisory bundle as CVE-2026-34950. The same patched build closes every CVE in the bundle, so the remediation procedure for CVE-2026-35039 matches the primary write-up.

What is different about CVE-2026-35039?

fast-jwt provides fast JSON Web Token (JWT) implementation. From 0.0.1 to before 6.2.0, setting up a custom cacheKeyBuilder method which does not properly create unique keys for different tokens can lead to cache collisions. This could cause tokens to be mis-identified during the verification process leading to valid tokens returning claims from different valid tokens and users being mis-identified as other users based on the wrong token.

Impact is consistent with the bundle: compromise of the affected component as described in the vendor advisory. The patched build closes every code path in the advisory in one update.

How to fix CVE-2026-35039

Apply the patched build per the primary write-up: How to Fix CVE-2026-34950.

For a quick check, confirm the running version of fast-jwt:

# Confirm the installed version via your package manager
dpkg -l | grep -i fast-jwt   # Debian/Ubuntu
rpm -qa | grep -i fast-jwt   # RHEL/CentOS/Rocky

Frequently asked questions

Is CVE-2026-35039 being actively exploited?

Not at the time of writing. It is not listed in CISA's Known Exploited Vulnerabilities catalog. That status can change, so monitor the vendor advisory and the KEV catalog if the system is exposed.

How severe is CVE-2026-35039?

CVSS rates it 9.1 (Critical). Use that score to set your patch priority alongside the other items in your queue.

Do I have to take fast-jwt offline to apply the patch?

It depends on the deployment. High-availability or clustered installs can usually patch one node at a time with no full outage. Standalone installs typically need a short restart. Always follow the vendor's documented upgrade steps.

What if my vulnerability scanner still flags CVE-2026-35039 after I patch?

Re-run the scan after a service restart, then confirm the scanner's plugin set is up to date. Some scanners detect by banner version only and lag the official fix metadata by a release.

References

• Official vendor advisory: https://github.com/nearform/fast-jwt/security/advisories/GHSA-rp9m-7r4c-75qg
• NVD entry: https://nvd.nist.gov/vuln/detail/CVE-2026-35039
• CISA KEV catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog
• Primary write-up: How to Fix CVE-2026-34950

*Written by Sai Kiran Pandrala. Last verified 2026-05-25. Part of the Nearform fast-jwt advisory bundle. Full procedure at how-to-fix-cve-2026-34950.*