CVE-2026-9537 Mojo::JWT versions before 1.02 for Perl verify HMAC signatures with a non-constant-time string comparison
Attackers can exploit timing side-channels in HMAC verification to forge JWT tokens, bypassing authentication in applications using this Perl library.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-9537?
CVE-2026-9537 is a medium-severity vulnerability in JBERGER Mojo::JWT, published on 17 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Mojo::JWT versions before 1.02 for Perl verify HMAC signatures with a non-constant-time string comparison.
The decode() method compares the supplied signature to the recomputed HMAC with Perl's eq operator, which stops at the first differing byte, so the comparison time varies with the number of matching leading bytes.
A caller that decodes attacker supplied tokens leaks the expected signature through this timing variation, which can be aggregated over many requests to recover the signature and forge a token.
Weakness: CWE-208
Which versions are affected by CVE-2026-9537?
Linux distribution packages (1)
perl-Mojo-JWT openSUSE:Tumbleweed | All versions | 1.20.0-2.1 |
How do I fix CVE-2026-9537?
Upgrade to a fixed version.
Is CVE-2026-9537 being exploited?
There is no known exploitation of CVE-2026-9537 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-9537, GHSA-3rp9-gq85-w2mf, UBUNTU-CVE-2026-9537, openSUSE-SU-2026:11450-1.