F5 NGINX Plus/NGINX Open Source prior 37.0.1.1/R32 P7/R36 P5 ngx_http_rewrite_module heap-based overflow

CVSS Meta Temp Score
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Current Exploit Price (≈)
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CTI Interest Score
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7.9$0-$5k0.00

Summaryinfo

A vulnerability described as critical has been identified in F5 NGINX Plus and NGINX Open Source. This affects an unknown part of the component ngx_http_rewrite_module. The manipulation results in heap-based overflow. This vulnerability is reported as CVE-2026-9256. The attack can be launched remotely. No exploit exists. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability classified as critical has been found in F5 NGINX Plus and NGINX Open Source. Affected is an unknown code block of the component ngx_http_rewrite_module. The manipulation with an unknown input leads to a heap-based overflow vulnerability. CWE is classifying the issue as CWE-122. A 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(). This is going to have an impact on confidentiality, integrity, and availability. CVE summarizes:

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.

The advisory is available at my.f5.com. This vulnerability is traded as CVE-2026-9256 since 05/21/2026. The exploitability is told to be difficult. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. The technical details are unknown and an exploit is not available. The structure of the vulnerability defines a possible price range of USD $0-$5k at the moment (estimation calculated on 05/26/2026).

The vulnerability scanner Nessus provides a plugin with the ID 316569 (Linux Distros Unpatched Vulnerability : CVE-2026-9256), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 37.0.1.1, R32 P7 or R36 P5 eliminates this vulnerability.

The vulnerability is also documented in the databases at Tenable (316569) and EUVD (EUVD-2026-31444). If you want to get best quality of vulnerability data, you may have to visit VulDB.

Productinfo

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CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CNA CVSS-B Score: 🔒
CNA CVSS-BT Score: 🔒
CNA Vector: 🔒

CVSSv3info

VulDB Meta Base Score: 8.1
VulDB Meta Temp Score: 7.9

VulDB Base Score: 8.1
VulDB Temp Score: 7.7
VulDB Vector: 🔒
VulDB Reliability: 🔍

CNA Base Score: 8.1
CNA Vector: 🔒

CVSSv2info

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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Heap-based overflow
CWE: CWE-122 / CWE-119
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Nessus ID: 316569
Nessus Name: Linux Distros Unpatched Vulnerability : CVE-2026-9256

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: NGINX Plus/NGINX Open Source 37.0.1.1/R32 P7/R36 P5

Timelineinfo

05/21/2026 CVE reserved
05/22/2026 +1 days Advisory disclosed
05/22/2026 +0 days VulDB entry created
05/26/2026 +4 days VulDB entry last update

Sourcesinfo

Vendor: f5.com

Advisory: K000161377
Status: Confirmed

CVE: CVE-2026-9256 (🔒)
GCVE (CVE): GCVE-0-2026-9256
GCVE (VulDB): GCVE-100-365202
EUVD: 🔒

Entryinfo

Created: 05/22/2026 17:33
Updated: 05/26/2026 08:36
Changes: 05/22/2026 17:33 (76), 05/23/2026 05:30 (1), 05/26/2026 08:36 (2)
Complete: 🔍
Cache ID: 216::103

If you want to get best quality of vulnerability data, you may have to visit VulDB.

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