Vulnerability record · CVE-2026-1525 · published 12 March 2026
CVE-2026-1525: Nodejs undici http request smuggling vulnerability
Nodejs · Undici
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. Who is impacted: * Applications using undici.request(), undici.Client, or similar low-level APIs with headers passed as flat arrays * Applications that accept user-controlled header names without case-normalization Potential consequences: * Denial of Service: Strict HTTP parsers (proxies, servers) will reject requests with duplicate Content-Length headers (400 Bad Request) * 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
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. Who is impacted: * Applications using undici.request(), undici.Client, or similar low-level APIs with headers passed as flat arrays * Applications that accept user-controlled header names without case-normalization Potential consequences: * Denial of Service: Strict HTTP parsers (proxies, servers) will reject requests with duplicate Content-Length headers (400 Bad Request) * 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:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Affected products
1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.
References
| Link | Tags |
|---|---|
| https://cna.openjsf.org/security-advisories.html | Vendor Advisory |
| https://cwe.mitre.org/data/definitions/444.html | Technical Description |
| https://github.com/nodejs/undici/security/advisories/GHSA-2mjp-6q6p-2qxm | MitigationVendor Advisory |
| https://hackerone.com/reports/3556037 | Permissions Required |
| https://www.rfc-editor.org/rfc/rfc9110.html#section-8.6 | Technical Description |
Track CVE-2026-1525 inside VULONE
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Related vulnerabilities
Same products first, then exploited flaws of the same weakness class.
Source: NIST National Vulnerability Database (record CVE-2026-1525), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.
