CVE-2026-19534 · GHSA-rfgv-xxqx-mfg5
undici vulnerable to Denial of Service via unrequested WebSocket subprotocol
- Risk score
- 62/100
- CVSS
- 7.5 v3.1
- Exploit chance (30 days)
- 0.4%
- Published
- 29 Sep 2026
Open in the live forecast Today's forecast
What to know
- What it is
- 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 termina…
- Affected
- undici (npm) >= 6.7.0, < 6.28.1; undici (npm) >= 7.0.0, < 7.29.1; undici (npm) >= 8.0.0, < 8.10.2
- Fix
- Upgrade undici to 6.28.1 or 7.29.1 or 8.10.2 (whichever matches your release line) or later.
- Exploitation
- No known exploitation
Story map
At a glance
undici: Amber, patch this week. 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 termina…
The flaws
- CVE-2026-19534: Undici vulnerable to Denial of Service via unrequested WebSocket subprotocol (CVSS 7.5 · EPSS 0%)
- CVE-2026-84961: Undici vulnerable to TLS certificate validation bypass via dropped connect options in BalancedPool (CVSS 7.4 · EPSS 0%)
- CVE-2026-85152: Undici vulnerable to cross-origin cache poisoning via missing origin isolation in interceptors (CVSS 7.4 · EPSS 0%)
- CVE-2026-18149: Undici vulnerable to Denial of Service via orphaned RetryHandler response body (CVSS 5.9 · EPSS 0%)
The fix
Fix: Upgrade undici to 6.28.1 or 7.29.1 or 8.10.2 (whichever matches your release line) or later.
Who is exposed: undici (npm) >= 6.7.0, < 6.28.1; undici (npm) >= 7.0.0, < 7.29.1; undici (npm) >= 8.0.0, < 8.10.2
Where it stands
- No known exploitation
Connects to
- Same weakness: CWE-248 (CWE-248). 62 other warnings in 30 days
Why it is Amber
- CVSS 7.5 high
- Remotely exploitable without logging in
- On your watchlist: npm
Affected packages
| Package | Ecosystem | Vulnerable | Fixed in |
|---|---|---|---|
| undici | npm | >= 6.7.0, < 6.28.1 | 6.28.1 |
| undici | npm | >= 7.0.0, < 7.29.1 | 7.29.1 |
| undici | npm | >= 8.0.0, < 8.10.2 | 8.10.2 |
References
- https://github.com/advisories/GHSA-rfgv-xxqx-mfg5
- https://github.com/nodejs/undici/security/advisories/GHSA-rfgv-xxqx-mfg5
- https://nvd.nist.gov/vuln/detail/CVE-2026-19534
- https://github.com/nodejs/undici/commit/2af0faf88b906d3127a360c3ac75164c0f95e5a5
- https://github.com/nodejs/undici/commit/6615e0175e9b635bcd2e3e87a47daa82f6f5b728
- https://github.com/nodejs/undici/commit/66e12816064cf3068f63bd134748b7fc4e779bad
- https://cna.openjsf.org/security-advisories.html
- https://github.com/nodejs/undici/releases/tag/v6.28.1
- https://github.com/nodejs/undici/releases/tag/v7.29.1
- https://github.com/nodejs/undici/releases/tag/v8.10.2
Original description
### 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.
Last activity 29 Sep 2026. Patch Forecast updates every hour.