Vulnerability Snapshot
CVE-2026-42533 is rated CRITICAL — exploitation is trivial or already observed in the wild and impact is severe. Patch immediately, not on the next maintenance window.
Executive Summary
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 a
Source
How Vulnios Detects This
Vulnios scans for this vulnerability using Trivy and Grype for CVE matching against your container images and OS package manifests and Nuclei templates that probe live HTTP surfaces for the published exploit pattern. Run a scan against your environment to see whether you are exposed; findings are linked back to the original CVE record so triage starts with the patch path already known.
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Related Threat Alerts
- USN-8563-2: nginx regression
- F5 Patches Multiple NGINX, BIG-IP Vulnerabilities
- CVE-2026-42055 NGINX ngx_http_proxy_v2_module and ngx_http_grpc_module vulnerability
- CVE-2026-48142 NGINX ngx_http_charset_module vulnerability
- F5 issues out-of-band patches for critical NGINX vulnerabilities
- USN-8398-3: nginx vulnerability
Frequently Asked Questions
What is CVE-2026-42533?
CVE-2026-42533 is a critical-severity vulnerability tracked under the Common Vulnerabilities and Exposures program. 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 denia
Am I affected?
Affected technology is listed in the Affected Products section above. If your asset inventory contains any of them, assume in-scope until you can prove otherwise.
How urgent is the response?
Critical: do not wait for your normal patch cycle. Verify exposure today, apply the vendor patch immediately, and add detection rules for any post-exploit indicators.
How do I remediate?
Apply the vendor patch listed in the upstream advisory linked under Sources. If the patch is not yet available, follow the vendor-supplied workaround (often a config flag or feature disable) and add detections for the published exploit pattern in your SIEM. Re-scan after the patch lands to confirm the finding clears.
Where can I track exploitation activity?
Watch CISA's Known Exploited Vulnerabilities catalog for CVE-2026-42533. Cross-reference with public exploit databases and your own SIEM/IDS for indicator-of-compromise patterns. Vulnios tracks KEV status automatically and surfaces it on the asset findings view.
How does Vulnios help with this?
Vulnios continuously cross-references your asset inventory against the live CVE feed (NVD, vendor advisories, CISA KEV, and curated OSINT). When a new CVE matches your environment, you get a prioritized finding with the severity, KEV status, exploit-prediction (EPSS), and a direct path to the vendor patch. You can start a free scan from the homepage.
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