CyberSecBulletin
CVE-2026-9256NVD status: Modified

NGINX Plus: Heap-based Buffer Overflow

Published Updated By the CyberSecBulletin desk

CVE-2026-9256 is a high-severity heap-based buffer overflow vulnerability in NGINX Plus from F5, with a CVSS 3.1 base score of 8.1 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists versions 37.0.1.1, R36 P5, R32 P7 as the first without the flaw, so updating NGINX Plus to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 10.9% chance of exploitation within 30 days, which is in the top 4.07% of all scored CVEs.

Patch this week

EPSS places it among the vulnerabilities most likely to be exploited soon.

What to do

  1. Update NGINX Plus to 37.0.1.1 or R36 P5 or R32 P7, whichever matches your release line, or a later version.
  2. Update NGINX Open Source to 1.31.1 or 1.30.2, whichever matches your release line, or a later version.
  3. Update Nginx Gateway Fabric to 2.6.2 or a later version.
  4. Read the advisory on my.f5.com for workarounds and exact fixed builds.
  5. Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.

Affected products and versions

VendorProductAffected versionsFixed in
F5NGINX Plus37.0 up to, but not including, 37.0.1.1; R36 up to, but not including, R36 P5; R32 up to, but not including, R32 P737.0.1.1, R36 P5, R32 P7
F5NGINX Open Source1.31.0 up to, but not including, 1.31.1; 1.30.0 up to, but not including, 1.30.2; 0.1.17 through 0.9.71.31.1, 1.30.2
Red HatRed Hat Enterprise Linux 10Not specified in the recordNot stated
Red HatRed Hat Enterprise Linux 8Not specified in the recordNot stated
Red HatRed Hat Enterprise Linux 9Not specified in the recordNot stated
Red HatRed Hat Discovery 2Not specified in the recordNot stated
Red HatRed Hat Hardened ImagesNot specified in the recordNot stated
Red HatRed Hat Update Infrastructure 5Not specified in the recordNot stated
Red HatRed Hat Lightspeed proxy 1Not specified in the recordNot stated
F5Dos4.3.0 through 4.7.0; 4.9.0Not stated
F5Nginx Gateway Fabric1.3.0 through 1.6.2; 2.0.0 up to, but not including, 2.6.22.6.2
F5Nginx Ingress Controller3.5.0 through 3.7.2; 4.0.0 through 4.0.1; 5.0.0 up to, but not including, 5.4.35.4.3
F5Nginx Instance Manager2.17.0 up to, but not including, 2.22.12.22.1
F5Waf4.10.0 through 4.16.0; 5.2.0 through 5.8.0; 5.9.0 through 5.13.0Not stated
Red HatDiscoveryNot specified in the recordNot stated
Red HatHardened ImagesNot specified in the recordNot stated
Red HatUpdate Infrastructure5.0 up to, but not including, 5.25.2
DebianDebian Linux11.0Not stated
Red HatEnterprise Linux8.0; 9.0; 10.0Not stated

Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
NetworkCan be exploited remotely over a network, including the internet.
Attack complexity
HighSuccess depends on conditions outside the attacker's control.
Privileges required
NoneNo account or login is needed.
User interaction
NoneNo action by a victim is required.
Scope
UnchangedImpact stays within the vulnerable component.
Confidentiality
HighAll data handled by the component can be read.
Integrity
HighData or code can be modified at will.
Availability
HighThe component can be taken down completely.

Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H. Scored by CNA (f5.com).

Scoring systemScoreSeverityScored by
CVSS 4.09.2CriticalCNA (f5.com)
CVSS 3.18.1HighCNA (f5.com)
CVSS 3.18.1HighCNA

Official 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.

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Heap-based Buffer Overflow

The product writes past the end of a buffer that was allocated on the heap.

How developers prevent this class of flaw

  • Pre-design: Use a language or compiler that performs automatic bounds checking.
  • Use an abstraction library to abstract away risky APIs. Not a complete solution.
  • Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index checking. D3-SFCV (Stack Frame Canary Validation) from D3FEND discusses canary-based detection in detail.

More Heap-based Buffer Overflow vulnerabilities (CWE-122)

Timeline

  1. CVE record published.
  2. CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
  3. Record last changed materially (score, affected products, status or references).

References

Third-party and government advisories

Other vulnerabilities in NGINX Plus

All NGINX Plus vulnerabilities

Recent Heap-based Buffer Overflow vulnerabilities

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