VulnerabilityDeferred

CVE-2026-9537

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.

MEDIUM 5.3EPSS 0.32%

Does this matter?

Lower severity and a low EPSS score (0.32%). Track it; it rarely justifies an emergency change on its own.

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.

CVSS 3.1: 5.3 MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
EPSS: 0.32% probability · 25th percentile
CISA KEV: Not listed
Weakness: CWE-208
Source: 9b29abf9-4ab0-4765-b253-1875cd9b441e

References

Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.