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.
Metrics
Affected Vendors & Products
References
History
Thu, 18 Jun 2026 20:45:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| First Time appeared |
Undici
Undici undici |
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| Vendors & Products |
Undici
Undici undici |
Thu, 18 Jun 2026 04:45:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| 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. | |
| Title | undici WebSocket client vulnerable to denial of service via cumulative fragment bypass | |
| Weaknesses | CWE-400 CWE-770 |
|
| References |
| |
| Metrics |
cvssV3_1
|
Status: PUBLISHED
Assigner: openjs
Published:
Updated: 2026-06-17T17:29:42.926Z
Reserved: 2026-05-27T07:10:38.904Z
Link: CVE-2026-9675
Updated: 2026-06-17T17:29:28.032Z
No data.
No data.
OpenCVE Enrichment
Updated: 2026-06-18T21:30:16Z