CVE-2026-9675: undici WebSocket client vulnerable to denial of service via cumulative fragment bypass
Vendor fix available · Affected: undici · Exploitation: not established
ExploitationNot established
Not in CISA KEV as of catalogue 2026.11.13 (13 Nov)
- In CISA KEV: not seen
- Exploited (reported): not seen
- Scanning observed: not seen
- Proof of concept public: not seen
- Not establishedNothing in the sources we check
Higher than 37% of scored CVEs
DescriptionNVD
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.
On the Atlas
Every published CVE is on the CyberSIXT Atlas, grouped by weakness, vendor and month.
Coverage1 article · 1 outlet
First in our coverage: SecurityOnline, 22 Jun.
- Undici npm package flaws threaten Node.js apps with leaks and DoSSecurityOnline · first in our coverage · mentions it in passing
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