Answer in brief
CVE-2026-12151 records a High severity (CVSS 7.5) vulnerability in undici WebSocket client vulnerable to denial of service via fragment count bypass. The current sources do not mark it as known exploited. The current feed maps undici/undici (generic), undici (npm), undici (npm), undici (npm). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 7.5. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps undici/undici (generic), undici (npm), undici (npm), undici (npm). Check affected ranges and fixed versions before updating.
| Product | Affected versions | Fixed versions |
|---|---|---|
| cpe:2.3:a:nodejs:undici:*:*:*:*:*:node.js:*:* | Not reported | Not reported |
| Package | Affected range | Fixed version |
|---|---|---|
| undici/undicigeneric | >=0 <6.26.0 || >=7.0.0 <7.28.0 || >=8.0.0 <8.5.0 | 6.26.0, 7.28.0, 8.5.0 |
| undicinpm | <6.27.0 | 6.27.0 |
| undicinpm | >=7.0.0,<7.28.0 | 7.28.0 |
| undicinpm | >=8.0.0,<8.5.0 | 8.5.0 |
Published upstream
Jun 17, 2026
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Sep 11, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Jun 19, 2026
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.
Quoted source text, attributed separately from HOL analysis.