{"id":"UBUNTU-CVE-2026-18540","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.","modified":"2026-09-16T14:01:37.079117813Z","published":"2026-09-04T18:17:00Z","upstream":["CVE-2026-18540"],"references":[{"type":"REPORT","url":"https://ubuntu.com/security/CVE-2026-18540"},{"type":"REPORT","url":"https://www.cve.org/CVERecord?id=CVE-2026-18540"},{"type":"REPORT","url":"https://github.com/nodejs/undici/security/advisories/GHSA-r53p-7pc4-xj5r"}],"affected":[{"package":{"name":"node-undici","ecosystem":"Ubuntu:24.04:LTS","purl":"pkg:deb/ubuntu/node-undici?arch=source&distro=noble"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["5.22.1+dfsg1+~cs20.10.10.2-1ubuntu1","5.26.3+dfsg1+~cs23.10.12-2"],"ecosystem_specific":{"binaries":[{"binary_name":"node-llhttp","binary_version":"9.1.3~5.26.3+dfsg1+~cs23.10.12-2"},{"binary_name":"node-undici","binary_version":"5.26.3+dfsg1+~cs23.10.12-2"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-18540.json"}},{"package":{"name":"node-undici","ecosystem":"Ubuntu:26.04:LTS","purl":"pkg:deb/ubuntu/node-undici?arch=source&distro=resolute"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["7.3.0+dfsg1+~cs24.12.11-2","7.16.0+dfsg+~cs3.2.0-2","7.18.2+dfsg+~cs3.2.0-1","7.18.2+dfsg+~cs3.2.0-1build1"],"ecosystem_specific":{"binaries":[{"binary_name":"node-undici","binary_version":"7.18.2+dfsg+~cs3.2.0-1build1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-18540.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N"},{"type":"Ubuntu","score":"medium"}]}