Time-of-check Time-of-use (TOCTOU) Race Condition Affecting undici package, versions <6.27.0>=7.0.0 <7.28.0>=8.0.0 <8.5.0
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
Do your applications use this vulnerable package?
In a few clicks we can analyze your entire application and see what components are vulnerable in your application, and suggest you quick fixes.
Test your applications- Snyk IDSNYK-JS-UNDICI-17372752
- published18 Jun 2026
- disclosed17 Jun 2026
- creditUnknown
Introduced: 17 Jun 2026
CVE-2026-6733 (opens in a new tab)How to fix?
Upgrade undici to version 6.27.0, 7.28.0, 8.5.0 or higher.
Overview
undici is an An HTTP/1.1 client, written from scratch for Node.js
Affected versions of this package are vulnerable to Time-of-check Time-of-use (TOCTOU) Race Condition in the HTTP/1.1 client when an attacker-controlled upstream server injects an unsolicited response onto an idle keep-alive socket after a request completes. An attacker can cause responses to be delivered to the wrong requests by sending crafted HTTP responses through a compromised or malicious upstream server.
Note: This is only exploitable if the upstream HTTP/1.1 server is attacker-controlled or compromised and keep-alive connection reuse is enabled.
Workaround
This vulnerability can be mitigated by disabling keep-alive connection reuse by setting keepAliveTimeout: 0 on the Client or Pool.