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CVE-2026-9675— undici WebSocket client vulnerable to denial of service via cumulative fragment bypass

Quick assessment

Affected
undici undici
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Node.js undici是Node.js基金会开源的一个HTTP/1.1客户端。 Node.js undici 8.0.0版本、8.1.0版本、8.2.0版本、8.3.0版本、8.4.0版本存在资源管理错误漏洞，该漏洞源于未对分片未压缩消息的累积大小强制执行配置限制，导致内存耗尽并拒绝服务。

CVSS 7.5 · High EPSS 0.49% · P41

Affected Version Matrix 2

VendorProduct Version RangeStatus
undici undici 8.0.0< 8.5.0 affected
8.5.0 unaffected
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I. Basic Information for CVE-2026-9675

Vulnerability Information
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Vulnerability Title
undici WebSocket client vulnerable to denial of service via cumulative fragment bypass
Source: CVE Program / CVE List V5
Vulnerability Description
Impact: The undici WebSocket client enforces maxPayloadSize per-frame but does not enforce the cumulative size of fragmented uncompressed messages. A malicious WebSocket server can stream many small fragments that each pass per-frame validation but collectively exceed the configured limit, causing unbounded memory growth in the client process. The result is memory exhaustion and a denial of service. Affected applications are those using the undici WebSocket client (new WebSocket(...)) that can be induced to connect to an attacker-controlled or compromised WebSocket endpoint. This is a regression specific to undici 8.1.0. The 6.25.0 line shipped the equivalent cumulative check from the start and is unaffected. The 7.x line never had the maxPayloadSize feature and is also unaffected. Patches: Upgrade to undici >= 8.5.0. Workarounds: No workaround is available. The fix must be applied through an upgrade.
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
未加控制的资源消耗(资源穷尽)
Source: CVE Program / CVE List V5
Vulnerability Title
Node.js undici 资源管理错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Node.js undici是Node.js基金会开源的一个HTTP/1.1客户端。 Node.js undici 8.0.0版本、8.1.0版本、8.2.0版本、8.3.0版本、8.4.0版本存在资源管理错误漏洞，该漏洞源于未对分片未压缩消息的累积大小强制执行配置限制，导致内存耗尽并拒绝服务。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
undici undici 8.0.0 ~ 8.5.0 -

II. Public POCs for CVE-2026-9675

# POC Description Source Link Shenlong Link
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Qwen3.6-35B-A3B · 9051 chars
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III. Intelligence Information for CVE-2026-9675

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Vendor Advisories for CVE-2026-9675 (1)

Same Patch Batch · undici · 2026-06-17 · 8 CVEs total

CVE-2026-12151 7.5 HIGH undici WebSocket client vulnerable to denial of service via fragment count bypass
CVE-2026-6734 7.5 HIGH undici vulnerable to cross-origin request routing via SOCKS5 proxy pool reuse
CVE-2026-9697 7.4 HIGH undici vulnerable to TLS certificate validation bypass via dropped requestTls in SOCKS5 Pr
CVE-2026-9679 5.9 MEDIUM undici vulnerable to HTTP header injection via Set-Cookie percent-decoding
CVE-2026-9678 5.9 MEDIUM undici vulnerable to cross-user information disclosure via shared cache whitespace bypass
CVE-2026-6733 3.7 LOW undici vulnerable to HTTP response queue poisoning via keep-alive socket reuse
CVE-2026-11525 3.7 LOW undici vulnerable to Set-Cookie SameSite attribute downgrade via permissive substring matc

IV. Related Vulnerabilities

Same product: undici
Same vendor: undici
Same weakness: CWE-400

V. Comments for CVE-2026-9675

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