Heap-based buffer overflow in NGINX Plus and NGINX Open Source - CVE-2026-42055
Published: June 18, 2026
Vulnerability identifier: #VU134861
CSH Severity: High
CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:U/U:Amber
CVE-ID: CVE-2026-42055
CWE-ID: CWE-122
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: F5 Networks
Affected software:
NGINX Plus
NGINX Open Source
NGINX Plus
NGINX Open Source
Detailed vulnerability description
The vulnerability allows a remote attacker to execute arbitrary code or cause a denial of service.
The vulnerability exists due to heap-based buffer overflow in ngx_http_proxy_v2_module and ngx_http_grpc_module when proxying HTTP/2 traffic with large headers while creating an upstream request. A remote attacker can send large headers to execute arbitrary code or cause a denial of service.
Exploitation requires a non-default configuration in which proxy_http_version is set to 2 or grpc_pass is used, ignore_invalid_headers is set to off, and the large_client_header_buffers per-buffer size is larger than 2 megabytes. This is a data plane issue only.
How to mitigate CVE-2026-42055
Install security update from vendor's website.