{"cve":"CVE-2026-1525","nvd":{"published":"2026-03-12T20:16:02.670","modified":"2026-06-17T10:15:59.927","status":"Analyzed","description":"Undici allows duplicate HTTP Content-Length headers when they are provided in an array with case-variant names (e.g., Content-Length and content-length). This produces malformed HTTP/1.1 requests with multiple conflicting Content-Length values on the wire.\n\nWho is impacted:\n\n  *  Applications using undici.request(), undici.Client, or similar low-level APIs with headers passed as flat arrays\n  *  Applications that accept user-controlled header names without case-normalization\n\n\nPotential consequences:\n\n  *  Denial of Service: Strict HTTP parsers (proxies, servers) will reject requests with duplicate Content-Length headers (400 Bad Request)\n  *  HTTP Request Smuggling: In deployments where an intermediary and backend interpret duplicate headers inconsistently (e.g., one uses the first value, the other uses the last), this can enable request smuggling attacks leading to ACL bypass, cache poisoning, or credential hijacking","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","score":9.8},"cwes":["CWE-444"],"references":["https://cna.openjsf.org/security-advisories.html","https://cwe.mitre.org/data/definitions/444.html","https://github.com/nodejs/undici/security/advisories/GHSA-2mjp-6q6p-2qxm","https://hackerone.com/reports/3556037","https://www.rfc-editor.org/rfc/rfc9110.html#section-8.6"],"products":["nodejs:undici"],"source":"nvd","synced_at":"2026-10-19T22:25:53.701907451+00:00"},"epss":{"cve":"CVE-2026-1525","score":0.00524,"percentile":0.44459,"date":"2026-10-31"},"kev":null,"osv":[{"id":"GHSA-2mjp-6q6p-2qxm","url":"https://osv.dev/vulnerability/GHSA-2mjp-6q6p-2qxm","summary":"Undici has an HTTP Request/Response Smuggling issue","modified":"2026-09-10T03:50:36.493109202Z","packages":[{"ecosystem":"npm","name":"undici","purl":"pkg:npm/undici","ranges":["<6.24.0"],"fixed":["6.24.0"]},{"ecosystem":"npm","name":"undici","purl":"pkg:npm/undici","ranges":[">=7.0.0 <7.24.0"],"fixed":["7.24.0"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}