CVE-2026-1526 Nodejs CVE debrief

Who should care

Developers and administrators using the undici WebSocket client in Node.js applications should be aware of this vulnerability and take steps to mitigate it. This includes updating to a patched version of undici and implementing additional security measures to prevent denial-of-service attacks. Organizations using affected versions of undici should prioritize patching and consider implementing compensating controls to prevent exploitation

Technical summary

The undici WebSocket client is vulnerable to a denial-of-service attack via unbounded memory consumption during permessage-deflate decompression. When a WebSocket connection negotiates the permessage-deflate extension, the client decompresses incoming compressed frames without enforcing any limit on the decompressed data size. This allows a malicious WebSocket server to send a small compressed frame that expands to an extremely large size in memory, causing the Node.js process to exhaust available memory and crash or become unresponsive. The vulnerability exists in the PerMessageDeflate.decompress() method, which accumulates all decompressed chunks in memory and concatenates them into a single Buffer without checking whether the total size exceeds a safe threshold

Defensive priority

High priority should be given to patching affected systems and implementing additional security measures to prevent denial-of-service attacks. This includes updating to a patched version of undici and monitoring for suspicious WebSocket activity

Recommended defensive actions

• Update to a patched version of undici
• Implement additional security measures to prevent denial-of-service attacks
• Monitor for suspicious WebSocket activity
• Consider implementing compensating controls to prevent exploitation
• Review and update incident response plans to address potential denial-of-service attacks

Evidence notes

The CVE-2026-1526 vulnerability was published on March 12, 2026, and modified on June 30, 2026. The vulnerability has a CVSS score of 7.5 and is considered high severity. The vulnerability exists in the PerMessageDeflate.decompress() method, which accumulates all decompressed chunks in memory and concatenates them into a single Buffer without checking whether the total size exceeds a safe threshold. A malicious WebSocket server can send a small compressed frame that expands to an extremely large size in memory, causing the Node.js process to exhaust available memory and crash or become unresponsive

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.