Encoding Error in NGINX Open Source - CVE-2026-42926

Vulnerability identifier: #VU131376

CSH Severity: Medium

CVSS v4: 6.9 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-42926

CWE-ID:

Exploitation vector: Remote access

Exploit availability: No public exploit available

The vulnerability allows a remote attacker to inject arbitrary HTTP/2 frame headers and payload bytes into the upstream connection.

The vulnerability exists due to encoding error in the ngx_http_proxy_v2_module module when proxying HTTP/2 traffic with proxy_http_version set to 2 and using proxy_set_body. A remote attacker can send crafted input to inject arbitrary HTTP/2 frame headers and payload bytes into the upstream connection.

This can lead to desynchronization between NGINX and the upstream HTTP/2 peer. There is no control plane exposure; this is a data plane issue only.

NGINX Open Source
Fedora
nginx-mod-js-challenge
nginx-mod-vts
nginx-mod-fancyindex
nginx-mod-headers-more
nginx-mod-brotli
nginx-mod-modsecurity
nginx-mod-naxsi
nginx

Install security update from vendor's website.

NGINX Open Source - update to 1.30.1
nginx-mod-js-challenge - update to 0^20230517.gitda6852d-7.fc44
nginx-mod-vts - addressed in versions 0.2.4-9.fc42, 0.2.4-9.fc43, 0.2.4-9.fc44
nginx-mod-fancyindex - addressed in versions 0.6.0-4.fc42, 0.6.0-4.fc43, 0.6.0-4.fc44
nginx-mod-headers-more - addressed in versions 0.39-9.fc42, 0.39-9.fc43, 0.39-9.fc44
nginx-mod-brotli - addressed in versions 1.0.0~rc-9.fc42, 1.0.0~rc-9.fc43, 1.0.0~rc-9.fc44
nginx-mod-modsecurity - addressed in versions 1.0.4-10.fc42, 1.0.4-10.fc43, 1.0.4-10.fc44
nginx-mod-naxsi - addressed in versions 1.6-17.fc42, 1.6-17.fc43, 1.6-17.fc44
nginx - addressed in versions 1.30.1-1.fc42, 1.30.1-1.fc43, 1.30.1-1.fc44

• https://my.f5.com/manage/s/article/K000161131

• Multiple vulnerabilities in NGINX Open Source and NGINX Plus
• Fedora 44 update for nginx, nginx-mod-brotli, nginx-mod-fancyindex, nginx-mod-headers-more, nginx-mod-js-challenge, nginx-mod-modsecurity, nginx-mod-naxsi, nginx-mod-vts
• Fedora 43 update for nginx, nginx-mod-brotli, nginx-mod-fancyindex, nginx-mod-headers-more, nginx-mod-modsecurity, nginx-mod-naxsi, nginx-mod-vts
• Fedora 42 update for nginx, nginx-mod-brotli, nginx-mod-fancyindex, nginx-mod-headers-more, nginx-mod-modsecurity, nginx-mod-naxsi, nginx-mod-vts