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🛡️ CVE-2026-2229 — undici

🟠 CVSS 8.0 — High ✅ No Known Exploit CWE-248 OSV
8.0
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

Undici has Unhandled Exception in WebSocket Client Due to Invalid server_max_window_bits Validation

Impact

The 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:

1. The isValidClientWindowBits() function only validates that the value contains ASCII digits, not that it falls within the valid range 8-15

2. The createInflateRaw() call is not wrapped in a try-catch block

3. The resulting exception propagates up through the call stack and crashes the Node.js process

Patches

_Has the problem been patched? What versions should users upgrade to?_

Workarounds

_Is there a way for users to fix or remediate the vulnerability without upgrading?_

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is low, an attacker needs no privileges on the target. No user interaction is required. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality none, integrity none, availability high.

CVSS metrics in full

The score comes from this vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

  • Attack vector: Network — reachable from anywhere that can route to the service.
  • Attack complexity: Low — the attack works reliably, with no preparation.
  • Privileges required: None — an unauthenticated stranger can try it.
  • User interaction: None — nobody has to be tricked into anything.
  • Scope: Unchanged — the damage stays inside the vulnerable component.
  • Confidentiality impact: None.
  • Integrity impact: None.
  • Availability impact: High — total loss, or loss the attacker controls.

Weakness class

CVE-2026-2229 is classified as CWE-248: Uncaught Exception. An exception is thrown from a function, but it is not caught.

Affected software

CVE-2026-2229 is recorded against 1 package.

  • undici

Timeline and source

Published on 13 March 2026 and last revised on 19 August 2026. No public exploit is currently recorded for this entry. Record sourced from OSV.

References

github.com (Web)
nvd.nist.gov (Advisory)
hackerone.com (Web)
cna.openjsf.org (Web)
datatracker.ietf.org (Web)
github.com (Package)
nodejs.org (Web)

Other advisories for this package

undici has other advisories on record. If you are patching this one, these are worth checking on the same host:

Same weakness in other software

These advisories are the same class of weakness (CWE-248: Uncaught Exception) in other software:

CVE-2026-2229 on other distributions

Each distribution ships its own build and its own fixed version. Pick the one you run:

Details

Severity HIGH
CVSS Score 8.0
CVSS Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CWE CWE-248
Public Exploit ✅ No
Source OSV
Published 2026-03-13
Updated 2026-08-20
Modified 2026-08-19
Fix URL N/A

Affected Packages

Software From version Fixed in
undici — —

Site Security Check

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ⓘ Data Notice: The information presented above has been compiled from publicly available internet sources. Boteraser aggregates this data solely for informational purposes and does not independently classify, evaluate, or endorse any findings about the vulnerabilities listed. The accuracy and completeness of this information is the sole responsibility of the original publishers. Boteraser and its operators accept no liability for any decisions made based on this data.

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