USN-8563-2: nginx regression

unknownpublic exploitCVE-2026-42533 CVE-2026-56434 CVE-2026-60005

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)

CSIRTS triage

vendor: nginx product: nginx Denial of service Remote code execution

What: A remote attacker could exploit a vulnerability in nginx to cause it to crash or possibly execute arbitrary code.
Who is affected: Deployments of nginx that utilize certain map directives and external modules.
Urgency: Remediation is urgent due to the potential for denial of service and remote code execution.
Action: Update to the latest version of nginx to mitigate the vulnerabilities.

AI-assisted analysis generated from the source advisory — verify against the original.

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Details

Source: Ubuntu Security Notices (INTL · vendor-psirt · site)
Severity: unknown
Published: 2026-07-20
Exploitation: Not in CISA KEV at last sync

Original advisory: https://ubuntu.com/security/notices/USN-8563-2

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Moderate exploitation riskCVE-2026-425333.6% 30-day exploitation probability. Patch within normal cadence, watch for KEV listing. Riskier than 88% of all scored CVEs.
Low exploitation riskCVE-2026-564340.45% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 37% of all scored CVEs.
Low exploitation riskCVE-2026-600050.71% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 50% of all scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-42533	coverage & exploitation status	NVD · CVE.org
CVE-2026-56434	coverage & exploitation status	NVD · CVE.org
CVE-2026-60005	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.