---
title: "CVE-2026-9256\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-2026-9256?format=md
keywords: index, follow
---

# CVE-2026-9256

Publication date 22 May 2026

Last updated 6 June 2026

---

Ubuntu priority

**Medium**

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

## Cvss 3 Severity Score

**8.1 · High**

[Score breakdown](https://ubuntu.com/security/CVE-2026-9256?format=md#impact-score)

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## Description

NGINX Plus and NGINX Open Source have a vulnerability in the
ngx\_http\_rewrite\_module module. This vulnerability exists when a rewrite
directive uses a regex pattern with distinct, overlapping Perl-Compatible
Regular Expression (PCRE) captures (for example, ^/((.\*))$) and a
replacement string that references multiple such captures (for example,
$1$2) in a redirect or arguments context. An unauthenticated attacker along
with conditions beyond their control can exploit this vulnerability by
sending crafted HTTP requests. This may cause a heap buffer overflow in the
NGINX worker process leading to a restart. Additionally, attackers can
execute code on systems with Address Space Layout Randomization (ASLR)
disabled or when the attacker can bypass ASLR.
Note: Software versions which have reached End of Technical Support (EoTS)
are not evaluated.

## Status

Show unmaintained releases

| Package | Ubuntu Release | Status |
| --- | --- | --- |
| nginx | 26.04 LTS resolute | Fixed 1.28.3-2ubuntu1.2 |
| 25.10 questing | Fixed 1.28.0-6ubuntu1.4 |
| 24.04 LTS noble | Fixed 1.24.0-2ubuntu7.9 |
| 22.04 LTS jammy | Fixed 1.18.0-6ubuntu14.12 |
| 20.04 LTS focal | Fixed 1.18.0-0ubuntu1.7+esm1  Ubuntu Pro |
| 18.04 LTS bionic | Fixed 1.14.0-0ubuntu1.11+esm2  Ubuntu Pro |
| 16.04 LTS xenial | Fixed 1.10.3-0ubuntu0.16.04.5+esm7  Ubuntu Pro |
| 14.04 LTS trusty | Fixed 1.4.6-1ubuntu3.9+esm6  Ubuntu Pro |

---

* [How can I get the fixes?](https://ubuntu.com/security/cves/about#security)
* [What do statuses mean?](https://ubuntu.com/security/cves/about#statuses)
* [Patch details](https://ubuntu.com/security/CVE-2026-9256?format=md#patch-details)

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### Patch details

For informational purposes only. We recommend not to cherry-pick updates. [How can I get the fixes?](https://ubuntu.com/security/cves/about#security)

| Package | Patch details |
| --- | --- |
| nginx | * Upstream:   [3f135ae](https://github.com/nginx/nginx/commit/3f135ae2eb60ce376196c898a6c7cb4d774f7068) |

## Severity score breakdown

CVSS version:

CVSS v4.0

[CVSS v4.0](https://ubuntu.com/security/CVE-2026-9256?format=md)
[CVSS v3.0](https://ubuntu.com/security/CVE-2026-9256?format=md)

**Base score**

9.2 · Critical

* Base metrics

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

  | Parameter | Value |
  | --- | --- |
  | Base score | 9.2 · Critical |
  | Base + Threat score | - |
  | Base + Environmental score | - |
  | Base + Threat + Environmental score | - |

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

## References

* [MITRE](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2026-9256)
* [NVD](https://nvd.nist.gov/vuln/detail/CVE-2026-9256)
* [Launchpad](https://launchpad.net/bugs/cve/CVE-2026-9256)
* [Debian](https://security-tracker.debian.org/tracker/CVE-2026-9256)

### Related Ubuntu Security Notices (USN)

+ [USN-8354-1](https://usn.ubuntu.com/USN-8354-1)
+ nginx vulnerabilities
+ 1 June 2026

+ [USN-8375-1](https://usn.ubuntu.com/USN-8375-1)
+ nginx vulnerabilities
+ 3 June 2026

### Other references

* <https://www.cve.org/CVERecord?id=CVE-2026-9256>
* <https://my.f5.com/manage/s/article/K000161377>
* <http://www.openwall.com/lists/oss-security/2026/05/22/14>