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CVE-2026-42533

Status: AnalyzedCritical (9.2)—

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.

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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.

CVSS

Exploitation probability (EPSS)

EPSS (Exploit Prediction Scoring System, FIRST) estimates how likely a vulnerability is to be exploited in the wild within 30 days. It complements CVSS (impact) and CISA KEV (confirmed exploitation).

🎯 ATT&CK techniques

How this vulnerability is exploited and what the attacker gains, in MITRE ATT&CK terms.

Vulnerabilidad remota (AV:N, PR:N, UI:N) en NGINX accesible sin autenticación. El heap buffer overflow causa DoS del proceso worker (T1499.004); código ejecutable solo sin ASLR o con bypass (T1059), pero impacto primario es el colapso del servicio.

Inferred by our analysis agent from the official description, CVSS vector and CWE, and checked by a supervisor. May contain errors.

🛡️ ATT&CK mitigations that cover these techniques

Privileged Account ManagementFilter Network TrafficVulnerability ScanningRestrict Web-Based ContentNetwork SegmentationLimit Software Installation

Affected technologies (4)

F5 — Nginx Gateway FabricF5 — Nginx Ingress ControllerF5 — Nginx PlusF5 — WAF

CWEs

References

Raw JSON (NVD)

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