CVE-2026-18540
Dashboard / Vulnerabilities / CVE-2026-18540
Summary: undici vulnerable to downstream response splitting via retry interceptor
Details: undici's retry interceptor can append the body of a ranged retry response to bytes already delivered from an earlier partial response while still presenting the original response's status and headers. This happens when an upstream server delivers part of a body without a trustworthy resume checkpoint, for example a non-success response whose headers were already sent or a partial-content response with an unusable content range, then closes the connection and answers the resumed range request with more bytes. As a result the response body can be longer than the Content-Length that the application observes. An application that relays such a response to a downstream HTTP/1.1 peer without normalizing the framing can emit a body that exceeds the forwarded Content-Length, and the excess bytes can be interpreted as the start of a following response, which enables downstream response splitting or desynchronization. Exploitation requires an attacker-controlled upstream server and an application that forwards the response through a framing-sensitive path. This affects undici versions before 6.28.1, from 7.0.0 up to 7.29.1, and from 8.0.0 up to 8.10.2. Users should upgrade to undici 6.28.1, 7.29.1, or 8.10.2.
References: https://cna.openjsf.org/security-advisories.html, https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/18xxx/CVE-2026-18540.json, https://github.com/nodejs/undici/security/advisories/GHSA-r53p-7pc4-xj5r, https://nvd.nist.gov/vuln/detail/CVE-2026-18540
Affected packages
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