CVE-2026-35515
MEDIUMNest is a framework for building scalable Node.js server-side applications. Prior to 11.1.18, SseStream._transform() interpolates message.type and message.id directly into Server-Sent…
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Description
Nest is a framework for building scalable Node.js server-side applications. Prior to 11.1.18, SseStream._transform() interpolates message.type and message.id directly into Server-Sent Events text protocol output without sanitizing newline characters (\r, \n). Since the SSE protocol treats both \r and \n as field delimiters and \n\n as event boundaries, an attacker who can influence these fields through upstream data sources can inject arbitrary SSE events, spoof event types, and corrupt reconnection state. This vulnerability is fixed in 11.1.18.
Affected Products
nestnestjsDetection & mitigation playbook
Vendor / applianceDetect
Inventory every nestjs nest deployment and check each version against the affected-products list above. Because the exploit targets the running system rather than your application code, also watch for exploitation at the network and runtime layer — O3 flags the exploit behaviour from runtime telemetry and egress traffic even before a vulnerable build is confirmed.
Fix
Apply the nestjs nest security patch or hotfix for CVE-2026-35515 on the affected version, following the vendor advisory for your exact build.
Workarounds
Cut exposure now: restrict the management/admin interface to trusted networks, segment the device, and apply the vendor's recommended configuration mitigations and any WAF/IPS signature. O3's runtime protection blocks the exploit chain at execution, holding the line on unpatched or end-of-life systems until you can patch.
How O3 protects you
O3 detects and blocks CVE-2026-35515 exploitation at runtime: eBPF exploit-chain detection, plus L7 egress monitoring that catches the post-exploitation callback and severs the attacker's outbound channel.
Tailored to CVE-2026-35515. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-35515 being exploited in your environment?
O3's eBPF runtime sensors and L7 egress monitoring detect and block the CVE-2026-35515 exploit chain at execution — protecting unpatched and end-of-life systems until the vendor patch is applied.