NGINX EUVD-2026-30011

Requires attacker to achieve man-in-the-middle position on the network path between NGINX proxy and upstream SCGI or uWSGI backend servers. This means the attacker must compromise either the backend server itself, intermediate network devices (switches, routers), or gain access to network segments where proxy-to-backend traffic transits. Additionally, the NGINX configuration must actively use scgi_pass or uwsgi_pass directives to proxy requests to backend application servers - installations using only fastcgi_pass, proxy_pass (HTTP), or serving static content are not affected. The vulnerability is exploitable from network position (AV:N) without authentication to NGINX (PR:N) and without user interaction (UI:N), but the Present attack complexity (AT:P) reflects the specific network positioning requirement. Standard DMZ architectures where NGINX and backends communicate over isolated internal networks significantly limit exploitation surface compared to configurations where backend communication traverses shared or less-trusted network segments.

Real-world risk is moderate despite CVSS 8.3 score due to significant exploitation prerequisites. The CVSS vector (AV:N/AC:L/AT:P) indicates network-accessible attack but with Present attack complexity (AT:P), meaning specific conditions must exist. The critical limiting factor is requiring MITM capability between NGINX and upstream servers - attackers must compromise network segments typically considered trusted internal zones in standard architectures. EPSS data not provided but expected to be low given the architectural barrier. No CISA KEV listing indicates no confirmed widespread exploitation. No public exploit identified at time of analysis. The High confidentiality impact (VC:H) is significant if exploited, as memory disclosure could expose session tokens, credentials, or application data processed by the worker. The Low availability impact (VA:L) from potential worker restarts is operationally manageable with NGINX's master-worker architecture. Primary risk applies to environments where: (1) NGINX proxies to SCGI/uWSGI backends, (2) upstream server infrastructure is potentially compromised or on untrusted networks, (3) sensitive data transits through worker process memory. Organizations with hardened internal networks and secured backend tiers face lower practical risk. Priority should increase for multi-tenant hosting environments or configurations where upstream servers are externally managed.

An attacker compromises a backend uWSGI application server or gains control over network infrastructure between NGINX reverse proxy and upstream servers. The attacker intercepts legitimate backend responses and injects malicious SCGI or uWSGI protocol payloads with manipulated size parameters. NGINX's vulnerable parsing logic allocates excessive memory or performs out-of-bounds reads, allowing the attacker to extract sensitive data from worker process memory (session tokens, authentication credentials, other client data) or crash the worker to cause service disruption. The attack succeeds without any authentication to NGINX itself, exploiting the trust relationship between proxy and backend tiers.