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CVE-2026-109855— undici WebSocket client vulnerable to Denial of Service via failed HTTP/2 handshake

Quick assessment

Affected
undici undici
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

undici 是 Node.js 的 HTTP 客户端库。在版本 8.11.0 和 8.11.1 中，其实验性 WebSocket 客户端（在允许 HTTP/2 时默认启用）对通过 HTTP/2 进行的失败 WebSocket 握手处理不当：此时请求已被标记为已完成，因此中止操作（abort）成为空操作（no-op），导致底层的 HTTP/2 连接流保持打开状态，且未设置错误监听器。当恶意服务器随后关闭连接时，该孤立流会触发未处理的错误，从而导致 Node.js 进程退出。因此，远程未认证的服务器可通过向客户端发起

CVSS 7.5 · High EPSS 0.28% · P19

Possible ATT&CK Techniques 1 AI

T1499 · Endpoint Denial of Service

Affected Version Matrix 2

VendorProduct Version RangeStatus
undici undici 8.11.0< 8.11.2 affected
8.11.2 unaffected
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I. Basic Information for CVE-2026-109855

Vulnerability Information
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Vulnerability Title
undici WebSocket client vulnerable to Denial of Service via failed HTTP/2 handshake
Source: CVE Program / CVE List V5
Vulnerability Description
undici is an HTTP client library for Node.js. In versions 8.11.0 and 8.11.1, its experimental WebSocket client, which is enabled by default when HTTP/2 is allowed, mishandles a failed WebSocket handshake over HTTP/2: the request is already marked completed, so the abort becomes a no-op and the underlying HTTP/2 stream is left open with no error listener. When a malicious server then destroys the connection, the orphaned stream emits an unhandled error and the Node.js process exits. A remote, unauthenticated server can therefore crash any client that opens a WebSocket to it over HTTP/2, resulting in a denial of service. The issue is fixed in undici 8.11.2, and users should upgrade to 8.11.2 or later. As a workaround, set allowH2 to false to disable HTTP/2 for WebSocket connections, or avoid opening WebSocket connections to untrusted servers.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
未捕获的异常
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
undici undici 8.11.0 ~ 8.11.2 -

II. Public POCs for CVE-2026-109855

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III. Intelligence Information for CVE-2026-109855

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Other References for CVE-2026-109855 (1)

Same Patch Batch · undici · 2026-10-15 · 9 CVEs total

CVE-2026-87018 7.5 HIGH undici vulnerable to Denial of Service via TLS 1.2 certificate-changing renegotiation
CVE-2026-109869 7.5 HIGH undici vulnerable to Denial of Service via unhandled error on excessive content-encodings
CVE-2026-109383 7.4 HIGH undici vulnerable to TLS certificate validation bypass via dropped tls options in Agent
CVE-2026-109829 7.4 HIGH undici vulnerable to cache poisoning and cross-user disclosure via cross-origin redirects
CVE-2026-87029 5.9 MEDIUM undici vulnerable to Denial of Service via unhandled exception in the decompress intercept
CVE-2026-109932 5.9 MEDIUM undici WebSocket client vulnerable to Denial of Service via unbounded automatic PONG buffe
CVE-2026-109841 5.9 MEDIUM undici vulnerable to Subresource Integrity bypass via non-lowercase algorithm tokens
CVE-2026-109924 5.9 MEDIUM undici vulnerable to Denial of Service via unbounded memory in the EventSource parser

IV. Related Vulnerabilities

Same product: undici
Same vendor: undici
Same weakness: CWE-248

V. Comments for CVE-2026-109855

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