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Vulnerability record · CVE-2026-42055 · published 17 June 2026

CVE-2026-42055: F5 dos heap-based buffer overflow vulnerability

F5 · Dos

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.

9.2 CVSS 4.0 Critical EPSS 2.4% · top 16.9% CWE-122 · Heap-based buffer overflowCWE-787 · Out-of-bounds write
9.2CVSS 4.0 base score
2.4%EPSS exploitation probability, 30 days
NoNot in CISA KEV
11Affected product versions listed by NVD
13References
14 Sep 2026Last modified by NVD

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.

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:

Affected products

11 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://my.f5.com/manage/s/article/K000161584 Vendor Advisory
https://access.redhat.com/errata/RHSA-2026:27197 Third Party Advisory
https://access.redhat.com/errata/RHSA-2026:36331 Third Party Advisory
https://access.redhat.com/errata/RHSA-2026:36364 Third Party Advisory
https://access.redhat.com/errata/RHSA-2026:36618 Third Party Advisory
https://access.redhat.com/errata/RHSA-2026:36639 Third Party Advisory
https://access.redhat.com/errata/RHSA-2026:38847 Third Party Advisory
https://access.redhat.com/errata/RHSA-2026:44481 Third Party Advisory
https://access.redhat.com/errata/RHSA-2026:46836 Third Party Advisory
https://access.redhat.com/errata/RHSA-2026:58981
https://access.redhat.com/security/cve/CVE-2026-42055 Third Party Advisory
https://bugzilla.redhat.com/show_bug.cgi?id=2489866 Issue TrackingThird Party Advisory
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-42055.json Third Party Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2026-42055), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.