CVE-2026-42533: F5 Nginx Gateway Fabric

What is 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 variables before referencing the map output variable. Alternatively, the same result could be achieved by using a non-cacheable variable in a string expression under certain conditions. An unauthenticated attacker along with conditions beyond their control can exploit this vulnerability by sending crafted HTTP requests. This may cause a heap buffer overflow in the NGINX worker process leading to a restart. Additionally, attackers can execute code on systems with Address Space Layout Randomization (ASLR) disabled or when the attacker can bypass ASLR. Impact: This vulnerability may allow remote attackers to cause a denial-of-service (DoS) on the NGINX system or to possibly trigger a code execution. There is no control plane exposure; this is a data plane issue only. Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.

CVSS8.1 NVD 3.1

SeverityHIGH

ExploitationNo exploitation reported

EPSS1% · P59

Triage statusNo Known Exploit

ActionPatch this week

CVSS vectorCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

CWECWE-122

NVD published2026-07-15

NVD last modified2026-08-10

Timeline

2026-07-15Published to the U.S. National Vulnerability Database (NVD)
2026-07-20First covered in a defend.network daily briefing
2026-08-10NVD record last updated

Affected product

F5 Nginx Gateway Fabric

NVD also lists CPE entries for: F5 Nginx Gateway Fabric, F5 Nginx Ingress Controller, F5 Nginx Plus, F5 Waf

Remediation Steps

Apply the vendor security update for NGINX / F5 as a priority.
Restrict network exposure of the affected service to trusted sources until patched.
Review logs and detections for indicators of exploitation.
Confirm fixed versions against the official vendor advisory before deploying.

References

Referenced in our briefings & reports

Vulnerability Priority Report – Week 3 of July 2026 (July 20 – 26)
NGINX, WordPress, SonicWall RCEs under active exploitation; patched versions released (2026-07-20)

Browse all tracked CVEs in the defend.network CVE database →

🤖 This CVE page is generated by defend.network from NVD, CISA KEV, EPSS, and our verified daily briefings. Severity and exploitation data come from official sources; always verify remediation steps against the official vendor advisory before acting in production.