undici
CVE-2026-9675
HIGH
Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Network-reachable malicious server, no authentication or user interaction on the client beyond initiating the connection, availability-only impact via memory exhaustion, no confidentiality or integrity effect.
Primary rating from Vendor (openjs).
CVSS VectorVendor: openjs
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Lifecycle Timeline
1DescriptionCVE.org
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.
AnalysisAI
Denial-of-service in the undici WebSocket client (Node.js HTTP/WebSocket library) version 8.1.0 through versions prior to 8.5.0 allows a malicious or compromised WebSocket server to exhaust client memory by streaming many small fragmented frames that individually pass the per-frame maxPayloadSize check but cumulatively bypass any size limit. The flaw is a regression introduced in the 8.1.0 line; no public exploit identified at time of analysis. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires the victim Node.js application to (1) use the undici WebSocket client (new WebSocket(...) from undici, or Node core's global WebSocket which is backed by undici) at versions 8.1.0 through 8.4.x, and (2) be induced to establish an outbound WebSocket connection to an endpoint the attacker controls or has compromised. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 3.1 base score of 7.5 (AV:N/AC:L/PR:N/UI:N/C:N/I:N/A:H) accurately reflects an unauthenticated, network-reachable, low-complexity availability attack with no confidentiality or integrity impact. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An application using undici's WebSocket client connects to an attacker-controlled or attacker-influenced WebSocket URL - for example a webhook target, an agentic AI tool consuming a user-supplied ws:// URL, or a federated service endpoint. The malicious server upgrades the connection and then streams an indefinite sequence of small continuation frames (each under maxPayloadSize) without ever sending the FIN bit, causing the client to accumulate fragments in memory until the Node.js process is OOM-killed. … |
| Remediation | Vendor-released patch: undici 8.5.0 - upgrade the direct or transitive undici dependency to >= 8.5.0 per the maintainer advisory at https://github.com/nodejs/undici/security/advisories/GHSA-38rv-x7px-6hhq. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours: Inventory all Node.js applications and verify undici versions in use; document which systems connect to external WebSocket servers. …
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