CVE-2026-56434
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
- 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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Exploitation outlook
- Low exploitation risk0.45% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 37% of all EPSS-scored CVEs.
Advisory coverage (6)
- high[NEW] [high] NGINX NGINX Plus: Multiple vulnerabilitiescert-bund · 2026-07-30
- unknownUSN-8563-2: nginx regressionubuntu · 2026-07-20
- unknownUSN-8563-1: nginx vulnerabilitiesubuntu · 2026-07-20
- unknownMultiple vulnerabilities in F5 products (July 16, 2026)cert-fr-avis · 2026-07-16
- mediumCVE-2026-56434: NGINX Plus and NGINX Open Source have a vulnerability in the ngx_http_ssi_module module. This …nvd · 2026-07-15
- mediumCVE-2026-56434: NGINX ngx_http_ssi_module vulnerabilitymsrc · 2026-07-14
External references
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