SB2026071606 - Multiple vulnerabilities in NGINX Open Source

Description

This security bulletin contains information about 3 vulnerabilities.

1) Use-after-free (CVE-ID: CVE-2026-56434)

CWE-ID: CWE-416 - Use After Free

CVSSv4: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:H/SC:N/SI:N/SA:N/E:U/U:Green

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

The vulnerability exists due to use-after-free in the ngx_http_ssi_module module when processing responses from an upstream server with SSI enabled, proxy_pass configured, and proxy_buffering disabled. A remote attacker can control responses from an upstream server to cause a denial of service or modify memory contents.

Exploitation requires man-in-the-middle ability over upstream server responses. This is a data plane issue only.

2) Use of uninitialized resource (CVE-ID: CVE-2026-60005)

CWE-ID: CWE-908 - Use of Uninitialized Resource

CVSSv4: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:H/SC:N/SI:N/SA:N/E:U/U:Amber

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

The vulnerability exists due to use of an uninitialized resource in ngx_http_slice_module when handling requests with the slice directive and unnamed regex captures configured or during a background cache update. A remote attacker can send crafted requests to disclose limited memory contents or cause a denial of service.

The issue affects the NGINX worker process and is limited to the data plane. The module is not enabled by default and must be built with the --with-http_slice_module configuration parameter.

3) Heap-based buffer overflow (CVE-ID: CVE-2026-42533)

CWE-ID: CWE-122 - Heap-based Buffer Overflow

CVSSv4: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:U/U:Amber

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

The vulnerability exists due to heap-based buffer overflow in the map directive with regex matching when processing crafted HTTP requests that trigger regex capture variable references before the map output variable. A remote attacker can send crafted HTTP requests to execute arbitrary code or cause a denial of service.

Code execution is possible on systems with ASLR disabled or when ASLR can be bypassed. This is a data plane issue only.

Remediation

Install update from vendor's website.

References

• https://my.f5.com/manage/s/article/K000162098
• https://my.f5.com/manage/s/article/K000162100
• https://my.f5.com/manage/s/article/K000162097