---
title: "CVE-2026-59638\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-2026-59638?format=md
keywords: index, follow
---

# CVE-2026-59638

Publication date 3 August 2026

Last updated 31 August 2026

---

Ubuntu priority

**Medium**

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

## Cvss 3 Severity Score

**6.5 · Medium**

[Score breakdown](https://ubuntu.com/security/CVE-2026-59638?format=md#impact-score)

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## Description

In Bouncy Castle for Java before 1.85, JSSE hostname verifier CN-fallback
enabled by default despite documented opt-in. This issue also affects
Bouncy Castle for Java LTS before 2.73.12, and Bouncy Castle for Java FIPS
(BC-FJA) before bctls-fips 1.0.24 (1.0.X series), 2.0.24 (2.0.X series) and
2.1.24 (2.1.X series).

## Status

Show unmaintained releases

| Package | Ubuntu Release | Status |
| --- | --- | --- |
| bouncycastle | 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 |
| 16.04 LTS xenial | 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 v4.0

[CVSS v4.0](https://ubuntu.com/security/CVE-2026-59638?format=md)
[CVSS v3.0](https://ubuntu.com/security/CVE-2026-59638?format=md)

**Base score**

9.3 · Critical

* Base metrics

  | Parameter | Value |
  | --- | --- |
  | Attack vector | Network |
  | Attack complexity | Low |
  | Attack requirements | None |
  | Privileges required | None |
  | User interaction | None |
  | Vulnerable system - Confidentiality impact | High |
  | Vulnerable system - Integrity impact | High |
  | Vulnerable system - Availability impact | None |
  | Subsequent system - Confidentiality impact | None |
  | Subsequent system - Integrity impact | None |
  | Subsequent system - Availability impact | None |
* Scores

  | Parameter | Value |
  | --- | --- |
  | Base score | 9.3 · Critical |
  | Base + Threat score | - |
  | Base + Environmental score | - |
  | Base + Threat + Environmental score | - |

**Vector:** CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/U:Amber

## References

* [MITRE](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2026-59638)
* [NVD](https://nvd.nist.gov/vuln/detail/CVE-2026-59638)
* [Launchpad](https://launchpad.net/bugs/cve/CVE-2026-59638)
* [Debian](https://security-tracker.debian.org/tracker/CVE-2026-59638)

### Other references

* <https://www.cve.org/CVERecord?id=CVE-2026-59638>
* <https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%9059638>
* <https://github.com/bcgit/bc-java/commit/5ac55351cd1a8a7184d41c96a7ee87df0770240a>
* <https://github.com/bcgit/bc-java/commit/799bd15320a6310a447863638aa3df64acef829b>