CVE WatchJul 15, 2026

CVE-2026-2229

ImpactThe undici WebSocket client is vulnerable to a denial-of-service attack due to improper validation of the server_max_window_bits param

CVSS

7.5

High

EPSS

0.9%

p55

KEV

—

Exploit Today

0-100

Published: Mar 12, 2026 · Last modified: Jul 15, 2026 · CWE-248 · CWE-1284

EPSS · 30d

0.9%EPSS · 30 days0.9%

2026-06-302026-07-16

Technical description

ImpactThe undici WebSocket client is vulnerable to a denial-of-service attack due to improper validation of the server_max_window_bits parameter in the permessage-deflate extension. When a WebSocket client connects to a server, it automatically advertises support for permessage-deflate compression. A malicious server can respond with an out-of-range server_max_window_bits value (outside zlib's valid range of 8-15). When the server subsequently sends a compressed frame, the client attempts to create a zlib InflateRaw instance with the invalid windowBits value, causing a synchronous RangeError exception that is not caught, resulting in immediate process termination. The vulnerability exists because: * The isValidClientWindowBits() function only validates that the value contains ASCII digits, not that it falls within the valid range 8-15 * The createInflateRaw() call is not wrapped in a try-catch block * The resulting exception propagates up through the call stack and crashes the Node.js process

Official references

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