CVE-2026-42055: f5 dos Heap-based Buffer Overflow

Vulnerability summary

CVE-2026-42055 is a critical (CVSS 9.2) Heap-based Buffer Overflow vulnerability in f5 dos. EPSS estimates a 6.54% chance of exploitation in the next 30 days, higher than 93.7% of scored vulnerabilities.

Timeline

1. 17-06-2026
   PublishedVulnerability first disclosed.
2. 14-09-2026
   Last modifiedVulnerability information updated.

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.

• CWE-122Heap-based Buffer OverflowA 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().
• CWE-787Out-of-bounds WriteThe product writes data past the end, or before the beginning, of the intended buffer.
• CWE-131Incorrect Calculation of Buffer SizeThe product does not correctly calculate the size to be used when allocating a buffer, which could lead to a buffer overflow.