CyberSecBulletin
CVE-2026-42055NVD status: Modified

NGINX Open Source: Out-of-bounds Write

Published Updated By the CyberSecBulletin desk

CVE-2026-42055 is a high-severity out-of-bounds write vulnerability in NGINX Open Source 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 1.31.2, 1.30.3 as the first without the flaw, so updating NGINX Open Source to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 6.54% chance of exploitation within 30 days, which is in the top 6.1% of all scored CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Update NGINX Open Source to 1.31.2 or 1.30.3, whichever matches your release line, or a later version.
  2. Update NGINX Plus to 37.0.2.1 or R36 P6, whichever matches your release line, or a later version.
  3. Update Update Infrastructure to 5.2 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 Open Source1.13.10 up to, but not including, 1.31.2; 1.30.2 up to, but not including, 1.30.31.31.2, 1.30.3
F5NGINX Plus37.0 up to, but not including, 37.0.2.1; R36 up to, but not including, R36 P637.0.2.1, R36 P6
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 Openshift Data Foundation 4Not 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 through 2.6.3Not stated
F5Nginx Ingress Controller3.5.0 through 3.7.2; 4.0.0 through 4.0.1; 5.0.0 through 5.5.0Not stated
F5Nginx Instance Manager2.17.0 through 2.22.0Not stated
F5Waf4.10.0 through 4.16.0; 5.2.0 through 5.8.0; 5.9.0 through 5.13.1Not 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
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_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.

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

The underlying weakness: Out-of-bounds Write

The product writes data past the end, or before the beginning, of the intended buffer.

How developers prevent this class of flaw

  • Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, many languages that perform their own memory management, such as Java and Perl, are not subject to buffer overflows. Other languages, such as Ada and C#, typically provide overflow protection, but the protection can be disabled by the programmer. Be wary that a language's interface to native code may still be subject to overflows, even if the language itself is theoretically safe.
  • Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. Examples include the Safe C String Library (SafeStr) by Messier and Viega, and the Strsafe.h library from Microsoft. These libraries provide safer versions of overflow-prone string-handling functions.
  • 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 Out-of-bounds Write vulnerabilities (CWE-787)

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

Other vulnerabilities in NGINX Open Source

All NGINX Open Source vulnerabilities

Recent Out-of-bounds Write vulnerabilities

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