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Vulnerabilities

Vulnerability · CVE-2026-2229

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

Published Mar 12, 2026 · catalog updated Sep 4, 2026 · Red Hat

Check if you run it

No confirmed exploitation is on record for CVE-2026-2229. EPSS is 0.89%. Act only if a listed version of Red Hat is installed.

Gaps on this record

  • No version range is stored. A customer cannot check an installed version against this record.
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
High7.5
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.89%
Remediation
Advisory link
Affected products
cpe nodejs/undici

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

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

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  • cpe nodejs/undiciversion unspecified

How to fix CVE-2026-2229

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-2229. EPSS is 0.89%. Act only if a listed version of Red Hat is installed.

Which versions are affected?

Affected version ranges are not on this record. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-1284; CWE-248. EPSS 0.89%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Mar 12, 2026 · NIST NVD

    Detected

    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 val

  2. Sep 4, 2026 · NIST NVD

    Updated

    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 val

Sources

  • CSAF AdvisoriesVendor advisoryRHSA-2026:9742:CVE-2026-2229

    A flaw was found in the undici WebSocket client. A remote malicious server can exploit this vulnerability by sending a WebSocket frame with an invalid parameter within the permessage-deflate extension. This improper validation causes the client's Node.js process to terminate, lea

    security.access.redhat.com
  • CVE.orgVulnerability recordCVE-2026-2229

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-2229

    30-day exploitation probability 0.9%

    first.org
  • NIST NVDVulnerability recordCVE-2026-2229

    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-d

    nvd.nist.gov

References

Freshness

Last verified in this catalog Oct 18, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.