{"id":"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.","aliases":["GHSA-r53p-7pc4-xj5r"],"modified":"2026-09-06T03:30:16.315226224Z","published":"2026-09-04T17:15:50.619Z","database_specific":{"cwe_ids":["CWE-444"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/18xxx/CVE-2026-18540.json","cna_assigner":"openjs"},"references":[{"type":"ADVISORY","url":"https://cna.openjsf.org/security-advisories.html"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/18xxx/CVE-2026-18540.json"},{"type":"ADVISORY","url":"https://github.com/nodejs/undici/security/advisories/GHSA-r53p-7pc4-xj5r"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-18540"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/nodejs/undici","events":[{"introduced":"0"},{"fixed":"ffc8aa0fdd4c54024f384e57784d5047c8b4085a"},{"introduced":"1cfe0949053aac6267f11b919cee9315a27f1fd6"},{"fixed":"d39a83e7b0d631590c3b85b5cc0dbeab66c3a1d8"},{"introduced":"d7fbba51772deecb830a297647456a5e9f9fec57"},{"fixed":"5e541e0b9df7563e5766bbd469fbfe383d9ae6ca"}],"database_specific":{"source":"AFFECTED_FIELD","extracted_events":[{"introduced":"0"},{"fixed":"6.28.1"},{"introduced":"7.0.0"},{"fixed":"7.29.1"},{"introduced":"8.0.0"},{"fixed":"8.10.2"}]}}],"versions":["v8.10.1","v8.10.0","v6.28.0","v8.9.0","v7.29.0","v6.27.0","v7.28.0","v8.8.0","v8.7.0","v8.6.0","v8.5.0","v6.26.0","v7.27.2","v8.4.1","v8.4.0","v7.27.1","v7.27.0","v7.26.0","v6.25.0","v8.3.0","v8.2.0","v7.25.0","v7.24.8","v8.1.0","v8.0.3","v8.0.2","v8.0.1","v8.0.0","v7.24.7","v7.24.6","v7.24.5","v7.24.4","v7.24.3","v7.24.2","v6.24.1","v6.24.0","v7.24.1","v7.24.0","v6.23.0","v7.23.0","v7.22.0","v7.21.0","v7.20.0","v7.19.2","v7.19.1","v7.19.0","v7.18.2","v7.18.1","v7.18.0","v6.22.0","v7.17.0","v7.16.0","v7.15.0","v6.21.3","v7.14.0","v7.13.0","v7.12.0","v7.11.0","v7.10.0","v6.21.2","v7.9.0","v7.8.0","v7.7.0","v7.5.0","v7.6.0","v7.4.0","v6.21.1","v7.3.0","v7.2.3","v7.2.2","v7.2.1","v7.2.0","v7.1.1","v7.1.0","v7.0.0","v6.21.0","v6.20.1","v6.20.0","v6.19.8","v6.19.7","v6.19.6","v6.19.5","v6.19.4","v6.19.3","v6.19.2","v6.19.1","v6.19.0","v6.18.2","v6.18.1","v6.18.0","v6.17.0","v6.16.1","v6.16.0","v6.15.0","v6.14.1","v6.14.0","v6.13.0","v6.12.0","v6.11.1","v6.11.0","v6.10.2","v6.10.1","v6.10.0","v6.9.0","v6.8.0","v6.7.1","v6.7.0","v6.6.2","v6.6.1","v5.28.2","v6.6.0","v6.5.0","v6.4.0","v6.3.0","v6.2.1","v6.2.0","v6.1.0","v6.0.1","v6.0.0","v5.28.1","v5.28.0","v5.27.2","v5.27.1","v5.27.0","v5.26.5","v5.26.4","v5.26.3","v5.26.2","v5.26.1","v5.26.0","v5.23.4","v5.25.3","v5.25.2","v5.25.1","v5.25.0","v5.24.0","v5.23.0","v5.22.1","v5.22.0","v5.21.2","v5.21.1","v5.21.0","v5.20.0","v5.19.1","v5.19.0","v5.18.0","v5.17.1","v5.17.0","v5.16.0","v5.15.2","v5.15.1","v5.15.0","v5.14.0","v5.13.0","v5.12.0","v5.11.0","v5.10.0","v5.9.1","v5.8.2","v5.8.1","v5.8.0","v5.7.0","v5.6.1","v5.6.0","v5.5.1","v5.5.0","v5.4.0","v5.3.0","v5.2.0","v5.1.1","v5.1.0","v5.0.0","v4.16.0","v4.15.1","v4.15.0","v4.14.1","v4.14.0","v4.13.0","v4.12.2","v4.12.0","v4.11.3","v4.11.2","v4.11.1","v4.11.0","v4.10.4","v4.10.3","v4.10.2","v4.10.1","v4.10.0","v4.9.5","v4.9.4","v4.9.3","v4.9.2","v4.9.1","v4.9.0","v4.8.2","v4.8.1","v4.8.0","v4.7.3","v4.7.2","v4.7.1","v4.7.0","v4.6.0","v4.5.1","v4.5.0","v4.4.7","v4.4.6","v4.4.5","v4.4.4","v4.4.3","v4.4.2","v4.4.1","v4.3.1","v4.3.0","v4.2.2","v4.2.1","v4.1.1","v4.1.0","v4.0.0","v4.0.0-rc.8","v4.0.0-rc.7","v4.0.0-rc.5","v4.0.0-rc.4","v4.0.0-rc.3","v4.0.0-rc.2","v4.0.0-rc.1","v4.0.0-alpha.5","v4.0.0-alpha.4","v4.0.0-alpha.2","v4.0.0-alpha.1","v4.0.0-alpha.0","v3.3.1","v3.3.0","v3.2.0","v3.1.0","v3.0.0","v2.1.0","v2.0.7","v2.0.6","v2.0.5","v2.0.4","v2.0.3","v2.0.2","v2.0.1","v2.0.0","v1.3.1","v1.3.0","v1.2.6","v1.2.5","v1.2.2","v1.2.1","v1.2.0","v1.1.0","v1.0.3","v1.0.2","v1.0.1","v1.0.0"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/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"}]}