SB2026051401 - Multiple vulnerabilities in NGINX Open Source and NGINX Plus

Description

This security bulletin contains information about 6 vulnerabilities.

1) Out-of-bounds read (CVE-ID: CVE-2026-42934)

The vulnerability allows a remote attacker to disclose limited memory contents or cause a denial of service.

The vulnerability exists due to out-of-bounds read in ngx_http_charset_module when processing requests with charset, source_charset, charset_map, and proxy_pass configured with buffering disabled. A remote attacker can send crafted requests to disclose limited memory contents or cause a denial of service.

This issue affects the data plane only and requires the specific configuration to be enabled.

2) Use-after-free (CVE-ID: CVE-2026-40701)

The vulnerability allows a remote attacker to cause a denial of service or modify data in a limited manner.

The vulnerability exists due to use-after-free in ngx_http_ssl_module when handling requests with client certificate verification and OCSP checking enabled. A remote attacker can send requests that trigger the flaw to cause a denial of service or modify data in a limited manner.

This issue affects the data plane only. Exploitation requires the ssl_verify_client directive to be set to "on" or "optional," and the ssl_ocsp directive to be set to "on" or configured with the leaf parameter and a resolver.

3) Uncontrolled Memory Allocation (CVE-ID: CVE-2026-42946)

The vulnerability allows a remote attacker to disclose memory contents of the NGINX worker process or cause a denial of service.

The vulnerability exists due to memory allocation with excessive size value and use of out-of-range pointer offset in the ngx_http_scgi_module and ngx_http_uwsgi_module modules when processing responses from an upstream server via scgi_pass or uwsgi_pass. A remote attacker can control responses from an upstream server to disclose memory contents of the NGINX worker process or cause a denial of service.

Exploitation requires man-in-the-middle ability to control responses from an upstream server. There is no control plane exposure; this is a data plane issue only.

4) Heap-based buffer overflow (CVE-ID: CVE-2026-42945)

The vulnerability allows a remote attacker to cause a denial of service or execute arbitrary code.

The vulnerability exists due to heap-based buffer overflow in ngx_http_rewrite_module when processing crafted HTTP requests that reach configurations where a rewrite directive is followed by a rewrite, if, or set directive and unnamed PCRE captures are used with a replacement string containing a question mark. A remote attacker can send crafted HTTP requests to cause a denial of service or execute arbitrary code.

Code execution is possible on systems with address space layout randomization disabled. There is no control plane exposure; this is a data plane issue only.

5) Encoding Error (CVE-ID: CVE-2026-42926)

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.

6) Authentication Bypass by Spoofing (CVE-ID: CVE-2026-40460)

The vulnerability allows a remote attacker to bypass authorization or cause a denial of service.

The vulnerability exists due to authentication bypass by spoofing in the ngx_quic_module module when handling HTTP/3 QUIC traffic. A remote attacker can spoof their source IP address to bypass authorization or cause a denial of service.

There is no control plane exposure; this is a data plane issue only.

Remediation

Install update from vendor's website.

References

• https://my.f5.com/manage/s/article/K000161028
• https://my.f5.com/manage/s/article/K000161021
• https://my.f5.com/manage/s/article/K000161027
• https://my.f5.com/manage/s/article/K000161019
• https://my.f5.com/manage/s/article/K000161131
• https://my.f5.com/manage/s/article/K000161068