CVE-2026-9256: debian debian_linux Heap-based Buffer Overflow

Vulnerability summary

CVE-2026-9256 is a critical (CVSS 9.2) Heap-based Buffer Overflow vulnerability in debian debian_linux. EPSS estimates a 2.70% chance of exploitation in the next 30 days, higher than 85.7% of scored vulnerabilities.

Timeline

1. 22-05-2026
   PublishedVulnerability first disclosed.
2. 25-08-2026
   Last modifiedVulnerability information updated.

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.

• CWE-122Heap-based Buffer OverflowA heap overflow condition is a buffer overflow, where the buffer that can be overwritten is allocated in the heap portion of memory, generally meaning that the buffer was allocated using a routine such as malloc().