USN-8563-5: nginx vulnerability
Ubuntu ships improved nginx fix for CVE-2026-42533 after earlier patch regression; flaw allows remote crash and possible code execution.
USN-8563-5 provides a better fix for CVE-2026-42533 after the original fix from USN-8563-1 was backed out in USN-8563-2 because it caused a regression. The flaw stems from nginx incorrectly handling certain map directives using regex matching and capture variables, allowing a remote attacker to crash nginx, causing denial of service, or possibly execute arbitrary code. The original advisory also described a use-after-free in the ngx_http_ssi_module when configured with Server-Side Includes, proxy_pass, and proxy buffering.
- Improved fix for CVE-2026-42533 replaces regression-prone earlier patch
- Remote attacker can crash nginx or possibly execute arbitrary code
- Trigger involves map directives with regex matching and capture variables
- Third revision of the original USN-8563-1 nginx advisory
Vulnerabilities mentioned
All| CVE | Vulnerability | CVSS | EPSS | Signals | Published |
|---|---|---|---|---|---|
| CVE-2026-42533 | A vulnerability exists in NGINX Plus and NGINX Open Source when a map directive uses regex matching and a string expression references the map's regex capture… | 9.2 | <1% | PoC ×2 |
From the original article
USN-8563-1 fixed vulnerabilities in nginx. The fix for CVE-2026-42533 was backed out in USN-8563-2 because it could cause a regression. This update includes a better fix for CVE-2026-42533.
ubuntu.com
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