NGINX Heap Buffer Overflow via Large HTTP/2 Headers in Proxy Modules
CVE-2026-42055 Published on June 17, 2026
NGINX ngx_http_proxy_v2_module and ngx_http_grpc_module vulnerability
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.
Vulnerability Analysis
CVE-2026-42055 can be exploited with network access, and does not require authorization privileges or user interaction. This vulnerability is consided to have a high level of attack complexity. The potential impact of an exploit of this vulnerability is considered to be very high.
Weakness Type
Heap-based Buffer Overflow
A heap overflow condition is a buffer overflow, where the buffer that can be overwritten is allocated in the heap portion of memory, generally meaning that the buffer was allocated using a routine such as malloc().
Products Associated with CVE-2026-42055
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Affected Versions
F5 NGINX Open Source:- Version 1.13.10 and below 1.31.2 is affected.
- Version 1.30.2 and below 1.30.3 is affected.
- Version 37.0 and below 37.0.2.1 is affected.
- Version R36 and below R36 P6 is affected.