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...

Description

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.

Metrics

CVSS 3.1

8.1/10

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

CVSS 4.0

9.2/10

CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

EPSS Probability

3.60%

88.3th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-122

Affected Software

Vendor	Product	Versions
F5	Nginx Gateway Fabric	>= 1.3.0, <= 1.6.2
F5	Nginx Gateway Fabric	>= 2.0.0, < 2.6.7
F5	Nginx Ingress Controller	>= 3.5.0, <= 3.7.2
F5	Nginx Ingress Controller	>= 5.0.0, < 5.5.3
F5	Nginx Ingress Controller	>= 2026-lts-r1, < 2026-lts-r4
F5	Nginx Ingress Controller	4.0.0
F5	Nginx Ingress Controller	4.0.1
F5	Nginx Plus	>= 37.0.0.1, < 37.0.3.1
F5	Nginx Plus	>= r33, < r36
F5	Nginx Plus	r36
F5	Waf	>= 4.11.0, <= 4.16.0
F5	Waf	>= 5.2.0, <= 5.8.0
F5	Waf	>= 5.9.0, < 5.13.4

References

https://my.f5.com/manage/s/article/K000162097Vendor Advisory

Timeline

Published: Jul 15, 2026
Last Modified: Aug 10, 2026
Status: Analyzed

Frequently Asked Questions

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.

How severe is CVE-2026-42533?

CVE-2026-42533 has a CVSS score of 9.2/10 (CRITICAL severity). The EPSS model estimates a 3.60% probability of exploitation in the next 30 days.

How do I fix CVE-2026-42533?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

How Strix Helps

Related CVEs from 2026

View all 2026CVEs →