CVE-2026-2229

Summary

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

Affected Software

VendorProductVersion RangeStatus
undiciundici< 6.24.0; 7.0.0 < 7.24.0affected
undiciundici6.24.0: 7.24.0unaffected

Weaknesses

  • CWE-248: CWE-248 Uncaught exception
  • CWE-1284: CWE-1284 Improper validation of specified quantity in input

ADP Enrichment

CISA ADP Vulnrichment

  • SSVC:
  • Exploitation: none
    • Automatable: yes
    • Technical Impact: partial

undici: Undici: Denial of Service via invalid WebSocket permessage-deflate extension parameter

Additional References

References