F5 has issued out-of-band patches for two critical flaws in NGINX, the web server and reverse proxy that runs a large share of the internet. CVE-2026-42530 (a use-after-free in the HTTP/3 module) and CVE-2026-42055 (a heap overflow in the HTTP/2 proxy and gRPC modules), both rated 9.2, let a remote, unauthenticated attacker corrupt memory in an NGINX worker, crashing it for a denial of service and, where address-space randomization is disabled or bypassed, potentially running code. They affect non-default configurations across NGINX Open Source, Plus, Gateway Fabric, and Instance Manager. F5 has not seen exploitation yet, but its products are frequent attacker targets.
The 18-year-old heap overflow in NGINX's rewrite module, CVE-2026-42945, disclosed last week as part of the 'Rift' bug cluster, is now seeing real exploitation attempts. AI-native security firm VulnCheck says its honeypot networks have caught attackers probing the flaw, though the goal of the campaigns is not yet clear. The vulnerability lets an unauthenticated attacker crash NGINX worker processes by sending crafted HTTP requests. Turning that crash into remote code execution requires the target host to have Address Space Layout Randomization (ASLR) disabled, which is uncommon by default, but the worker-crash denial-of-service is exploitable on its own and rated urgent.
An AI-discovered bug hidden in NGINX since 2008 lets anyone on the internet crash NGINX worker processes or, with ASLR disabled, run code on the server using a single crafted HTTP request. The flaw, named NGINX Rift (CVE-2026-42945, CVSS 9.2), sits in the rewrite module that powers URL rewriting in almost every NGINX deployment. It triggers when a config uses a rewrite directive with unnamed regex captures and a question mark, followed by another rewrite, if, or set directive - a common pattern in API gateway setups. NGINX runs roughly a third of the websites on the public internet.
A CVSS 9.8 authentication bypass in nginx-ui, the popular open-source web management interface for Nginx servers, is being actively exploited in the wild. The flaw, codenamed MCPwn by Pluto Security, exists because the /mcp_message endpoint added for Model Context Protocol (AI integration) support only checks IP whitelisting - and the default whitelist is empty, meaning it allows all connections. One unauthenticated HTTP POST request lets an attacker invoke all MCP tools: rewrite Nginx config files, reload the server, intercept all traffic, and harvest admin credentials. Attackers chain it with CVE-2026-27944 (exposed encryption keys via the backup API) to extract the node_secret needed for full MCP access. Recorded Future flagged active exploitation and assigned a risk score of 94/100. Shodan shows 2,600 publicly exposed instances, mostly in China, the US, Indonesia, and Germany. Pluto Security's key lesson: AI integration endpoints expose the same capabilities as the core application but often skip its security controls.
TrustStrike Labs