CVE intelligence

CVE-2026-9256

Vulnerability intelligence

Published May 22, 2026Sources checked Nov 11, 2026

8.1HIGHCVSS out of 10

What this means

Review the available evidence

CVE-2026-9256 and is rated High severity with a CVSS score of 8.1. It is not in the current CISA KEV record we collected. That does not prove exploitation has not occurred.

What to do next

Remediation and response

Microsoft Security Response Center guidance

Vendor revision: May 28, 2026

CBL-Mariner Releases

Vendor-listed releases

1.28.3-4

CISA KEVNot listedBased on the latest collected catalog

EPSS10.9%Estimated 30-day exploitation probability

Ransomware useNot markedCISA KEV ransomware field

Threat actors0Source-linked actor relationships

Overview

What is CVE-2026-9256?

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.

Source: NVD