CyberBrief
Subscribe
8.1High

F5 Dos

CVE-2026-42055

NGINX Plus and NGINX Open Source have a vulnerability in the ngx_http_proxy_v2_module and ngx_http_grpc_module modules. This vulnerability exists when the proxy_http_version to 2 or grpc_pass directives are used to proxy HTTP/2 traffic, the ignore_invalid_headers directive is set to off, and the large_client_header_buffers directive size is larger than 2 megabytes. A remote, unauthenticated attacker, along with conditions beyond their control, could send large headers while creating an upstream request. This may cause a heap-based 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.

What this means for your business

  • It affects F5 Dos. It matters if your company, or a supplier that handles your data, runs it.
  • An attacker can use it remotely, over a network, without a login, and without anyone at your company clicking anything.
  • FIRST's prediction model gives it a 7% chance of attack attempts being seen in the next 30 days, ranking above 93% of all known flaws.

What to do

  1. 1Check whether your company or your suppliers run F5 Dos, and which version. The affected versions are listed further down this page.
  2. 2If you do, apply the vendor's fix. A patch or vendor advisory has been published.

Not sure if your company is exposed?

Fastnexa’s certified penetration testers can check whether attackers could use this flaw, or others like it, against your websites, apps and network. The full test is free for our first 10 founding clients until 31 December 2026.

Check if you’re exposedBook a call

Scoring

CVSS
8.1 (v3.1)
Vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
CVSS v4
9.2
Weakness
CWE-122
Assigned by
f5sirt@f5.com

Dates

Published
2026-06-17
Last modified
2026-09-14
Sources
NVD

Affected products

  • F5 Dos4.3.0 - 4.7.0, 4.9.0
  • F5 Nginx Gateway Fabric1.3.0 - 1.6.2, 2.0.0 - 2.6.3
  • F5 Nginx Ingress Controller3.5.0 - 3.7.2, 4.0.0 - 4.0.1, 5.0.0 - 5.5.0
  • F5 Nginx Instance Manager2.17.0 - 2.22.0
  • F5 Nginx Open Source1.0.0 - 1.30.2, 1.31.0 - 1.31.1
  • F5 Nginx Plus37.0.0.1 - 37.0.2.1, r33 - r36, r36
  • F5 Waf4.10.0 - 4.16.0, 5.2.0 - 5.8.0, 5.9.0 - 5.13.1
  • Redhat Discoveryall versions
  • Redhat Hardened Imagesall versions
  • Redhat Update Infrastructure5.0 - 5.2
  • Redhat Enterprise Linux8.0, 9.0, 10.0

As listed in the NVD configuration data. Not a statement about your estate.

References