Vulnerability · Published Jul 17, 2026 · Assigned by CPANSec
CVE-2026-9537Mojo::JWT versions before 1.02 for Perl verify HMAC signatures with a non-constant-time string comparison
Medium 5.3
In plain English
A medium-severity security flaw in Mojo::JWT from JBERGER. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 25% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | libmojo-jwt-perl | no fix listed | DEBIAN-CVE-2026-9537 |
| Debian:13 | libmojo-jwt-perl | no fix listed | DEBIAN-CVE-2026-9537 |
| Debian:14 | libmojo-jwt-perl | 1.02-1 | DEBIAN-CVE-2026-9537 |
| Ubuntu:22.04:LTS | libmojo-jwt-perl | no fix listed | UBUNTU-CVE-2026-9537 |
| Ubuntu:24.04:LTS | libmojo-jwt-perl | no fix listed | UBUNTU-CVE-2026-9537 |
| Ubuntu:26.04:LTS | libmojo-jwt-perl | no fix listed | UBUNTU-CVE-2026-9537 |
Affected products (as reported)
Weakness: CWE-208 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N