CVE-2026-12151: undici WebSocket client vulnerable to denial of service via fragment count bypass
Impact
The undici WebSocket client enforces maxPayloadSize on the cumulative byte count of fragments in a message but does not enforce a limit on the number of fragments. A malicious WebSocket server can stream many small or empty continuation frames that each pass per-frame and cumulative-size validation, collectively 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(...)) or the WebSocketStream API that can be induced to connect to an attacker-controlled or compromised WebSocket endpoint.
All releases starting at undici 6.17.0 are affected.
Patches
Upgrade to undici v6.27.0, v7.28.0 or v8.5.0.
Workarounds
No workaround is available. The fix must be applied through an upgrade.
Other sources
Impact: The undici WebSocket client enforces maxPayloadSize on the cumulative byte count of fragments in a message but does not enforce a limit on the number of fragments. A malicious WebSocket server can stream many small or empty continuation frames that each pass per-frame and cumulative-size validation, collectively 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(...)) or the WebSocketStream API that can be induced to connect to an attacker-controlled or compromised WebSocket endpoint.
All releases starting at undici 6.17.0 are affected.
Patches: Upgrade to undici = 6.26.0, = 7.28.0, or = 8.5.0. Workarounds: No workaround is available. The fix must be applied through an upgrade.
— IBM
Impact: The undici WebSocket client enforces maxPayloadSize on the cumulative byte count of fragments in a message but does not enforce a limit on the number of fragments. A malicious WebSocket server can stream many small or empty continuation frames that each pass per-frame and cumulative-size validation, collectively 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(...)) or the WebSocketStream API that can be induced to connect to an attacker-controlled or compromised WebSocket endpoint.
All releases starting at undici 6.17.0 are affected.
Patches: Upgrade to undici >= 6.26.0, >= 7.28.0, or >= 8.5.0. Workarounds: No workaround is available. The fix must be applied through an upgrade.
— Red Hat
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
npm/undicito a version that resolves this vulnerability.Fixed in 8.5.0 - Upgrade
Upgrade
npm/undicito a version that resolves this vulnerability.Fixed in 7.28.0 - Upgrade
Upgrade
npm/undicito a version that resolves this vulnerability.Fixed in 6.27.0 - Upgrade
Upgrade
undici WebSocket client / WebSocketStream APIto a version that resolves this vulnerability.Fixed in 6.26.0 - Upgrade
Upgrade
undici WebSocket client / WebSocketStream APIto a version that resolves this vulnerability.Fixed in 7.28.0 - Upgrade
Upgrade
undici WebSocket client / WebSocketStream APIto a version that resolves this vulnerability.Fixed in 8.5.0 - Upgrade
Upgrade
undici WebSocket client / WebSocketStream APIto a version that resolves this vulnerability.Fixed in 6.27.0
Event History
Frequently Asked Questions
What is the severity of CVE-2026-12151?
CVE-2026-12151 has a severity score of 7.5, indicating high risk.
What type of attack does CVE-2026-12151 facilitate?
CVE-2026-12151 enables a denial of service attack through fragment count bypass.
How do I fix CVE-2026-12151?
To mitigate CVE-2026-12151, update to the latest version of the undici WebSocket client that addresses this vulnerability.
Who is affected by CVE-2026-12151?
CVE-2026-12151 affects users of the undici WebSocket client integrated within npm packages.
What is the impact of CVE-2026-12151?
CVE-2026-12151 can lead to service disruption by allowing malicious servers to bypass fragment limitations.