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
Affected products
nodejs: undici
References10
- cna.openjsf.org/security-advisories.html Vendor Advisory
- github.com/nodejs/undici/security/advisories/GHSA-v9p9-hfj2-hcw8 Vendor Advisory
- datatracker.ietf.org/doc/html/rfc7692 Technical Description
- hackerone.com/reports/3487486 Permissions Required
- nodejs.org/api/zlib.html#class-zlibinflateraw Technical Description
- access.redhat.com/errata/RHSA-2026:13826
- access.redhat.com/errata/RHSA-2026:17789
- access.redhat.com/errata/RHSA-2026:21772
- access.redhat.com/errata/RHSA-2026:21931
- access.redhat.com/errata/RHSA-2026:34342
Metrics
- CVSS 3.1
-
7.5
HIGH
Score source: CNA
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H - EPSS — exploit probability
- 1% percentile: 63 · as of 12 November 2026
- CWE
- CWE-248CWE-1284
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