Encoding Error in NGINX Open Source - CVE-2026-42926
Published: May 14, 2026
Vulnerability identifier: #VU131376
CSH Severity: Medium
CVSS v4.0: 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/E:U/U:Green
CVE-ID: CVE-2026-42926
CWE-ID:
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: F5 Networks
Affected software:
NGINX Open Source
NGINX Open Source
Detailed vulnerability description
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.
How to mitigate CVE-2026-42926
Install security update from vendor's website.