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High severityNVD Advisory· Published Mar 12, 2026· Updated Mar 13, 2026

undici is vulnerable to Unhandled Exception in undici WebSocket Client Due to Invalid server_max_window_bits Validation

CVE-2026-2229

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

AI Insight

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Affected packages

Versions sourced from the GitHub Security Advisory.

PackageAffected versionsPatched versions
undicinpm
< 6.24.06.24.0
undicinpm
>= 7.0.0, < 7.24.07.24.0

Affected products

51

Patches

Vulnerability mechanics

References

7

News mentions

0

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