NGINX ngx_http_charset_module Heap Buffer Over-read in Worker Process
CVE-2026-42934 Published on May 13, 2026
NGINX ngx_http_charset_module vulnerability
NGINX Plus and NGINX Open Source have a vulnerability in the ngx_http_charset_module module. When charset, source_charset, and charset_map and proxy_pass with disabled buffering ("off") directives are configured, unauthenticated attackers can send requests that with conditions beyond the attackers' control to cause a heap buffer over-read in the NGINX worker process, leading to limited disclosure of memory or a restart.
Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.
Vulnerability Analysis
CVE-2026-42934 is exploitable 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 have a small impact on confidentiality, a small impact on integrity, and a small impact on availability.
Weakness Type
Out-of-bounds Read
The software reads data past the end, or before the beginning, of the intended buffer. Typically, this can allow attackers to read sensitive information from other memory locations or cause a crash. A crash can occur when the code reads a variable amount of data and assumes that a sentinel exists to stop the read operation, such as a NUL in a string. The expected sentinel might not be located in the out-of-bounds memory, causing excessive data to be read, leading to a segmentation fault or a buffer overflow. The software may modify an index or perform pointer arithmetic that references a memory location that is outside of the boundaries of the buffer. A subsequent read operation then produces undefined or unexpected results.
Products Associated with CVE-2026-42934
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Affected Versions
F5 NGINX Plus:- Version R37 and below * is unaffected.
- Version R36 and below R36 P4 is affected.
- Version R32 and below R32 P6 is affected.
- Version 1.31.0 and below * is unaffected.
- Version 0.3.50 and below 1.30.1 is affected.