SB2026061844 - Multiple vulnerabilities in NGINX

Description

This security bulletin contains information about 3 vulnerabilities.

1) Heap-based buffer overflow (CVE-ID: CVE-2026-42055)

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 ngx_http_proxy_v2_module and ngx_http_grpc_module when proxying HTTP/2 traffic with large headers while creating an upstream request. A remote attacker can send large headers to execute arbitrary code or cause a denial of service.

Exploitation requires a non-default configuration in which proxy_http_version is set to 2 or grpc_pass is used, ignore_invalid_headers is set to off, and the large_client_header_buffers per-buffer size is larger than 2 megabytes. This is a data plane issue only.

2) Use-after-free (CVE-ID: CVE-2026-42530)

CWE-ID: CWE-416 - Use After Free

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 use-after-free in the ngx_http_v3_module when processing a specially crafted HTTP/3 session that reopens a QPACK encoder stream. A remote attacker can send a specially crafted HTTP/3 session to execute arbitrary code or cause a denial of service.

Exploitation requires NGINX Open Source to be configured to use the HTTP/3 QUIC module. Code execution is possible on systems with ASLR disabled or when ASLR can be bypassed. There is no control plane exposure; this is a data plane issue only.

3) Out-of-bounds read (CVE-ID: CVE-2026-48142)

CWE-ID: CWE-125 - Out-of-bounds read

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

The vulnerability allows a remote attacker to disclose limited memory contents or cause a worker process restart.

The vulnerability exists due to out-of-bounds read in ngx_http_charset_module when serving or proxying content through a location block configured with both source_charset utf-8 and a charset directive. A remote attacker can send crafted requests to disclose limited memory contents or cause a worker process restart.

This is a data plane issue only, and exploitation also depends on conditions beyond the attacker's control.

Remediation

Install update from vendor's website.

References

• https://my.f5.com/manage/s/article/K000161584
• https://my.f5.com/manage/s/article/K000161616
• https://my.f5.com/manage/s/article/K000161585