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High

undici vulnerable to Denial of Service via unrequested WebSocket subprotocol

  • Disclosed: 29.09.2026
  • Updated: 11.10.2026 10:22

Impact

The undici WebSocket client throws an uncaught TypeError during the opening handshake when a server's 101 response includes a Sec-WebSocket-Protocol header that the client never requested. The throw occurs in a queueMicrotask callback with no surrounding try/catch, so it propagates as an uncaught exception and terminates the Node.js process. This is a remote, unauthenticated denial of service against any application that opens a WebSocket to an attacker controlled or compromised server, or over a plaintext ws:// connection subject to a machine-in-the-middle. It affects the default new WebSocket(url) usage, where no subprotocol is requested. Per RFC 6455 section 4.1, an unrequested subprotocol must fail the connection, not crash it.

All releases starting at undici 6.7.0 are affected.

Patches

Upgrade to undici 6.28.1, 7.29.1, or 8.10.2.

Workarounds

No workaround is available. The fix must be applied through an upgrade.

Affected software

Click a technology to see all vulnerabilities affecting it.

PlatformPackageVulnerable versionsFixed in
npm package undici >= 6.7.0, < 6.28.1, >= 7.0.0, < 7.29.1, >= 8.0.0, < 8.10.2 6.28.1, 7.29.1, 8.10.2

References

CVSS score 7.5/10
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness (CWE)
CWE-248, CWE-252
Platform
npm
Package
undici
Disclosed
29.09.2026
Updated
11.10.2026 10:22

Sources and licenses

OSV / GitHub Advisory Database - GHSA-rfgv-xxqx-mfg5 - CC BY 4.0

Vulnerability history: undici

All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.

All (46) in the archive
Total entries
46
First → latest
06.2022 09.2026
Without a fix
0
Exploited in attacks
0

Severity breakdown

  • High 13
  • Medium 21
  • Low 12

Disclosures per year

Severity:
  1. undici vulnerable to Denial of Service via unrequested WebSocket subprotocol this entry
    High · 7.5 CVE-2026-19534 >= 6.7.0, < 6.28.1, >= 7.0.0, < 7.29.1, >= 8.0.0, < 8.10.2 6.28.1, 7.29.1, 8.10.2
  2. undici vulnerable to TLS certificate validation bypass via dropped connect options in BalancedPool
    High · 7.4 CVE-2026-84961 >= 7.24.1, < 7.29.1, >= 8.0.0, < 8.10.2 7.29.1, 8.10.2
  3. undici vulnerable to cross-origin cache poisoning via missing origin isolation in interceptors
    High · 7.4 CVE-2026-85152 >= 8.10.0, < 8.10.2 8.10.2
  4. undici vulnerable to cross-user information disclosure and parse-time crash via degenerate private cache directives
    High · 7.4 CVE-2026-13697 >= 7.0.0, < 7.29.0, >= 8.0.0, < 8.9.0 7.29.0, 8.9.0
  5. undici WebSocket client vulnerable to denial of service via fragment count bypass
    High · 7.5 CVE-2026-12151 < 6.27.0, >= 7.0.0, < 7.28.0, >= 8.0.0, < 8.5.0 6.27.0, 7.28.0, 8.5.0
  6. undici vulnerable to cross-origin request routing via SOCKS5 proxy pool reuse
    High · 7.5 CVE-2026-6734 >= 7.23.0, < 7.28.0, >= 8.0.0, < 8.2.0 7.28.0, 8.2.0
  7. undici vulnerable to TLS certificate validation bypass via dropped requestTls in SOCKS5 ProxyAgent
    High · 7.4 CVE-2026-9697 >= 7.23.0, < 7.28.0, >= 8.0.0, < 8.5.0 7.28.0, 8.5.0
  8. undici WebSocket client vulnerable to denial of service via cumulative fragment bypass
    High · 7.5 CVE-2026-9675 >= 8.0.0, < 8.5.0 8.5.0
  9. Undici has Unbounded Memory Consumption in WebSocket permessage-deflate Decompression
    High · 7.5 CVE-2026-1526 < 6.24.0, >= 7.0.0, < 7.24.0 6.24.0, 7.24.0
  10. Undici has Unhandled Exception in WebSocket Client Due to Invalid server_max_window_bits Validation
    High · 7.5 CVE-2026-2229 < 6.24.0, >= 7.0.0, < 7.24.0 6.24.0, 7.24.0
  11. Undici: Malicious WebSocket 64-bit length overflows parser and crashes the client
    High · 7.5 CVE-2026-1528 >= 6.0.0, < 6.24.0, >= 7.0.0, < 7.24.0 6.24.0, 7.24.0
  12. Regular Expression Denial of Service in Headers
    High · 7.5 CVE-2023-24807 < 5.19.1 5.19.1
  13. ProxyAgent vulnerable to MITM
    High · 7.7 CVE-2022-32210 >= 4.8.2, < 5.5.1 5.5.1

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