---
title: "CVE-2026-9537\n    | Ubuntu"
description: Ubuntu is an open source software operating system that runs from the
  desktop, to the cloud, to all your internet connected things.
url: https://ubuntu.com/security/CVE-2026-9537?format=md
keywords: index, follow
---

# CVE-2026-9537

Publication date 17 July 2026

Last updated 7 August 2026

---

Ubuntu priority

**Medium**

[Why this priority?](https://ubuntu.com/security/cves/about#priority )

## Cvss 3 Severity Score

**5.3 · Medium**

[Score breakdown](https://ubuntu.com/security/CVE-2026-9537?format=md#impact-score)

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## 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.

## Status

Show unmaintained releases

| Package | Ubuntu Release | Status |
| --- | --- | --- |
| libmojo-jwt-perl | 26.04 LTS resolute | Needs evaluation |
| 24.04 LTS noble | Needs evaluation |
| 22.04 LTS jammy | Needs evaluation |
| 20.04 LTS focal | Needs evaluation |
| 18.04 LTS bionic | Needs evaluation |

---

* [How can I get the fixes?](https://ubuntu.com/security/cves/about#security)
* [What do statuses mean?](https://ubuntu.com/security/cves/about#statuses)

## Severity score breakdown

CVSS version:
CVSS v3.0

**Base score**

5.3 · Medium

* Base metrics

  | Parameter | Value |
  | --- | --- |
  | Attack vector | Network |
  | Attack complexity | Low |
  | Privileges required | None |
  | User interaction | None |
  | Scope | Unchanged |
  | Confidentiality impact | None |
  | Integrity impact | Low |
  | Availability impact | None |
* Scores

  | Parameter | Value |
  | --- | --- |
  | Base score | 5.3 · Medium |
  | Exploitability score | - |
  | Impact score | - |

**Vector:** CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

## References

* [MITRE](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2026-9537)
* [NVD](https://nvd.nist.gov/vuln/detail/CVE-2026-9537)
* [Launchpad](https://launchpad.net/bugs/cve/CVE-2026-9537)
* [Debian](https://security-tracker.debian.org/tracker/CVE-2026-9537)

### Other references

* <https://www.cve.org/CVERecord?id=CVE-2026-9537>
* <https://lists.security.metacpan.org/cve-announce/msg/41907805/>