CVE-2026-42533

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.

How to fix CVE-2026-42533

To remediate CVE-2026-42533, upgrade the affected package to a fixed version below.

• —upgrade to 1.26.3-r2 or later
• —upgrade to 1.30.4 or later
• —upgrade to 1.30.4 or later
• —no fix listed

Is CVE-2026-42533 being exploited?

Low — EPSS is 0.8%, meaning exploitation activity has not been observed at scale.

Affected packages (4)

• from 0, < 1.26.3-r2
• >= 0.9.6, < 1.30.4, >= 1.31.2, < 1.31.3
• >= 0.9.6, < 1.30.4, >= 1.31.2, < 1.31.3
• from 0

CVSS scores

References (4)

• ADVISORYsecurity-tracker.debian.org/tracker/CVE-2026-42533
• ADVISORYsecurity.alpinelinux.org/vuln/CVE-2026-42533
• WEBmy.f5.com/manage/s/article/K000162097
• WEBnvd.nist.gov/vuln/detail/CVE-2026-42533