# CVE-2026-9537: libmojo-jwt-perl: Mojo::JWT versions before 1.02 for Perl verify HMAC signatures with a non-constant-time string comparison

CVE-2026-9537 is fixed in libmojo-jwt-perl on 1 platform by DEBIAN-CVE-2026-9537 (version 1.02-1), released July 18, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-9537
- Priority: Routine
- CVSS: 5.3 (medium)
- EPSS: 0.0032
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jul 17, 2026

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | libmojo-jwt-perl Debian 14 | 1.02-1 | [DEBIAN-CVE-2026-9537](https://patchblox.com/security/data/fix/linux/debian-cve-2026-9537.md) | Jul 18, 2026 |

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Data as of 2026-11-08T00:53:09Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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