CVE-2026-19534: undici vulnerable to Denial of Service via unrequested WebSocket subprotocol
Vulnerability summary
CVE-2026-19534 is a high (CVSS 7.5) Uncaught Exception vulnerability in nodejs undici. EPSS estimates a 0.39% chance of exploitation in the next 30 days, higher than 33.7% of scored vulnerabilities.
Severe, CVSS 7.5 (CVE.org); no exploitation reported by the 5 checked sources; EPSS 0% (FIRST, 04-11-2026)
Source freshness unavailable
How is this decided?Advisory lineage
Upstream 0 · Downstream 11Timeline
- 04-09-2026PublishedVulnerability first disclosed.
- 04-09-2026Last modifiedVulnerability information updated.
Description
undici's WebSocket client crashes the whole Node.js process during the opening handshake when a server responds with a subprotocol that the client never requested. A default WebSocket connection sends no subprotocol, but if the server's 101 response includes a Sec-WebSocket-Protocol header, undici dereferences a null value while checking it against the requested list and throws an uncaught TypeError. Because that code runs inside a microtask with no surrounding error handling, the exception propagates and terminates the process under Node's default behavior, instead of gracefully failing the connection as required by the WebSocket protocol. Any application that opens a WebSocket to an attacker-controlled or compromised server, or over a plaintext connection subject to a machine-in-the-middle, can be crashed remotely without authentication in the default configuration. This affects undici versions from 6.7.0 up to 6.28.1, from 7.0.0 up to 7.29.1, and from 8.0.0 up to 8.10.2. Users should upgrade to undici 6.28.1, 7.29.1, or 8.10.2.
CVSS metrics
7 scores · 7 sources · 1 version- OSV · UbuntuEcosystem advisory · calculated7.5HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- OSV · DebianEcosystem advisory · calculated7.5HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- OSV · WolfiEcosystem advisory · calculated7.5HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- OSV · NpmEcosystem advisory · calculated7.5HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- OSV · ChainguardEcosystem advisory · calculated7.5HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- NVDNIST7.5HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS trend
Probability
0.39%
Chance of exploitation in the next 30 days
Percentile
34%
Versus all other CVEs
30-day change
No change 0.00 pp
From 0.39% on 05-10-2026
Known exploited
Compare KEV catalogs
CISA KEVNot in the CISA KEV catalog.
ENISA CNWNot in the ENISA CNW catalog.
CIRCLNot in the CIRCL catalog.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root causeAffected systems
Known conditions: network-reachable, no authentication, no user interaction (CVSS vector). Other conditions: not stated in public data.
Chainguard16 products
- actions-runner< 2.337.0-r2
- code-server< 4.139.1-r2
- commercial-gitlab-rails-ee-19.1< 19.1.7-r3
- commercial-gitlab-rails-ee-19.2< 19.2.7-r1
- commercial-gitlab-rails-ee-19.3< 19.3.3-r1
Wolfi4 products
- code-server< 4.139.1-r2
- lernaAll versions (No fix recorded) | < 10.0.1-r11
- prism< 5.16.0-r14
- renovate< 44.133.0-r0 | < 44.131.0-r1
Debian1 product
- node-undiciAll versions (No fix recorded) | < 8.10.2+dfsg+~cs3.2.2-1
Nodejs1 product
- undici≥ 6.7.0, < 6.28.1 | ≥ 7.0.0, < 7.29.1 | ≥ 8.0.0, < 8.10.2
Npm1 product
- undici≥ 6.7.0, < 6.28.1 | ≥ 7.0.0, < 7.29.1 | ≥ 8.0.0, < 8.10.2
Ubuntu1 product
- node-undiciAll versions (No fix recorded)
Undici1 product
- undici≥ 6.7.0, < 6.28.1 | ≥ 7.0.0, < 7.29.1 | ≥ 8.0.0, < 8.10.2
7 vendors · 25 products
