Instituto Nacional de ciberseguridad. Sección Incibe
Instituto Nacional de Ciberseguridad. Sección INCIBE-CERT

Go to Calendar     Go to Press Room     Go to Newsletters subscription

Search

CVE-2026-9256

Severity CVSS v4.0:
CRITICAL
Type:
CWE-122 Heap-based Buffer Overflow
Publication date:
22/05/2026
Last modified:
15/07/2026

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. <br /> <br /> <br /> Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.

Impact

Vector 4.0
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 CVSS v4.0 Severity and Metrics:

Base Score: 9.20 CRITICAL
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

Attack Vector (AV): Network
Attack Complexity (AC): High
Attack Requirements (AT): Present
Privileges Required (PR): None
User Interaction (UI): None
Confidentiality (VC): High
Integrity (VI): High
Availability (VA): High
Confidentiality (SC): None
Integrity (SI): None
Availability (SA): None

Base Score 4.0
9.20
Severity 4.0
CRITICAL
Vector 3.x
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H CVSS v3.1 Severity and Metrics:

Base Score: 8.10 HIGH
Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Attack Vector (AV): Network
Attack Complexity (AC): High
Privileges Required (PR): None
User Interaction (UI): None
Scope (S): Unchanged
Confidentiality (C): High
Integrity (I): High
Availability (A): High

Base Score 3.x
8.10
Severity 3.x
HIGH

Vulnerable products and versions

CPE From Up to
cpe:2.3:a:f5:nginx_open_source:*:*:*:*:*:*:*:* 0.1.17 (including) 0.9.7 (including)
cpe:2.3:a:f5:nginx_open_source:*:*:*:*:*:*:*:* 1.0.0 (including) 1.30.1 (including)
cpe:2.3:a:f5:nginx_open_source:1.31.0:*:*:*:*:*:*:*
cpe:2.3:a:f5:nginx_plus:*:*:*:*:*:*:*:* 37.0.0 (including) 37.0.1.1 (excluding)
cpe:2.3:a:f5:nginx_plus:*:*:*:*:*:*:*:* r32 (including) r36 (including)

To consult the complete list of CPE names with products and versions, see this page


References to Advisories, Solutions, and Tools