SB2026051921 - Debian update for nginx

Description

This security bulletin contains information about 5 vulnerabilities.

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

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:L/SC:N/SI:N/SA:N/E:U/U:Green

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.

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

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 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.

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

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:A/U:Red

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.

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

CWE-ID: CWE-789 - Uncontrolled Memory Allocation

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

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.

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

CWE-ID: CWE-290 - Authentication Bypass by Spoofing

CVSSv4: CVSS:4.0/AV:N/AC:L/AT:N/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 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://lists.debian.org/debian-security-announce/2026/msg00189.html