CVEs / CVE-2026-42533
CVE-2026-42533: F5 NGINX Plus vulnerability
- critical 9.2 CVSS 4.0 (from the CNA)
- Last changed at its sources
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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.
Affected and fixed versions
| Product | Affected | Fixed in |
|---|---|---|
| F5 NGINX Plus | from 37.0.0.1, before 37.0.3.1 | 37.0.3.1 |
| F5 NGINX Plus | from R36, before R36 P7 | R36 P7 |
| F5 NGINX Plus | from R33 onwards | — |
| F5 NGINX Open Source | from 1.31.2, before 1.31.3 | 1.31.3 |
| F5 NGINX Open Source | from 0.9.6, before 1.30.4 | 1.30.4 |
Exploitation
Not in the CISA Known Exploited Vulnerabilities catalog as of 4 Nov 2026.
Severity
| CVSS 4.0 | 9.2 criticalCVSS: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:XScored by the CNA ([email protected]) |
|---|---|
| Weakness | CWE-122 |
On the Stackurity blog
References
- CVE-2026-42533 on NVD
- CVE-2026-42533 on OSV
- https://my.f5.com/manage/s/article/K000162097 Vendor Advisory
Sources
Exploitation status from the CISA Known Exploited Vulnerabilities catalog. EPSS scores from FIRST. Descriptions, severity and references from the National Vulnerability Database. Open-source package versions from OSV (CC-BY 4.0). Text is shown as each source states it; Stackurity does not edit it. Check the vendor's advisory before acting.
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