{"id":"GHSA-qrxm-fqhp-jwvm","aliases":["CVE-2026-87018"],"title":"undici vulnerable to Denial of Service via TLS 1.2 certificate-changing renegotiation","description":"## Impact\n\nundici crashes the client process when a TLS 1.2 server renegotiates after the connection is established and presents a different, CA-trusted certificate whose hostname does not match the requested host. Node.js re-runs hostname verification on the renegotiated handshake and destroys the socket with `ERR_TLS_CERT_ALTNAME_INVALID`. undici's established socket error handler asserted that this error code could never occur, so the peer-controlled error became an uncaught `AssertionError` that terminates the Node.js process. Both the HTTP/1.1 and HTTP/2 paths are affected.\n\nA malicious or compromised HTTPS endpoint reached through undici or the global `fetch()` can crash the client with a single server-initiated renegotiation, taking down all in-flight requests and background work in the process. Only TLS 1.2 is affected, because TLS 1.3 does not support renegotiation. Exploitation does not require a CA compromise: the attacker controls the endpoint and can present two ordinary valid certificates, the first matching the requested URL and the second intentionally not matching it.\n\n## Patches\n\nUpgrade to undici 6.29.1, 7.30.1, or 8.12.2.\n\n## Workarounds\n\nRestrict outbound connections to TLS 1.3, for example by setting `connect: { minVersion: 'TLSv1.3', maxVersion: 'TLSv1.3' }` on the client or agent, so that renegotiation cannot occur, when the target endpoints support TLS 1.3.","severity":"high","score":7.5,"published":"2026-10-27T19:02:21.000Z","modified":"2026-10-27T19:15:22.403Z","withdrawn":false,"knownExploited":false,"affected":[{"ecosystem":"npm","name":"undici","ranges":[{"events":[{"introduced":"4.2.1"},{"fixed":"6.29.1"}],"type":"SEMVER"}],"versions":[],"fixed":["6.29.1"]},{"ecosystem":"npm","name":"undici","ranges":[{"events":[{"introduced":"7.0.0"},{"fixed":"7.30.1"}],"type":"SEMVER"}],"versions":[],"fixed":["7.30.1"]},{"ecosystem":"npm","name":"undici","ranges":[{"events":[{"introduced":"8.0.0"},{"fixed":"8.12.2"}],"type":"SEMVER"}],"versions":[],"fixed":["8.12.2"]}],"references":["https://github.com/nodejs/undici/security/advisories/GHSA-qrxm-fqhp-jwvm","https://nvd.nist.gov/vuln/detail/CVE-2026-87018","https://github.com/nodejs/undici/commit/12cfd96c3f430897656e3edc1c5e02be8c1cd309","https://github.com/nodejs/undici/commit/b40fbfc0651703cf9fa9f6ced68b679f28d8bb28","https://github.com/nodejs/undici/commit/e257e9f8fb42eedd50727b9cf65e548c8925e4a8","https://cna.openjsf.org/security-advisories.html","https://github.com/nodejs/undici","https://github.com/nodejs/undici/releases/tag/v6.29.1","https://github.com/nodejs/undici/releases/tag/v7.30.1","https://github.com/nodejs/undici/releases/tag/v8.12.2"],"sources":[{"name":"OSV","id":"GHSA-qrxm-fqhp-jwvm","modified":"2026-10-27T19:15:22.403573595Z","url":"https://osv.dev/vulnerability/GHSA-qrxm-fqhp-jwvm"}],"assessments":[{"source":"OSV","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","score":7.5}]}