USN-8563-2: nginx regression

USN-8563-1 fixed vulnerabilities in nginx. One of the fixes introduced ABI
changes that could cause issues with external modules. This update reverts
the fix for CVE-2026-42533 pending further investigation.

We apologize for the inconvenience.

Original advisory details:

It was discovered that nginx incorrectly handled certain map directives
using regex matching and capture variables. A remote attacker could use
this issue to cause nginx to crash, resulting in a denial of service, or
possibly execute arbitrary code. (CVE-2026-42533)

It was discovered that nginx had a use-after-free vulnerability in the
ngx_http_ssi_module module when configured with Server-Side Includes,
proxy_pass, and proxy buffering disabled directives. An attacker able to
intercept traffic and control responses from an upstream server could
possibly use this issue to cause nginx to crash, resulting in a denial of
service. (CVE-2026-56434)

It was discovered that nginx incorrectly handled certain requests in the
ngx_http_slice_module module. A remote attacker could possibly use this
issue to obtain sensitive information or cause nginx to crash, resulting
in a denial of service. (CVE-2026-60005)