Vulnerability Description
form-data is a library for creating readable multipart/form-data streams. In versions through 4.0.5, the `field` argument to `FormData#append` and the `filename` option are concatenated verbatim into the `Content-Disposition` header without escaping carriage return (CR), line feed (LF), or double-quote (") characters. An application that passes attacker-controlled data as a field name or filename (for example, an API gateway that turns JSON object keys into multipart field names) allows the attacker to terminate the header line and inject additional headers, or to smuggle entire additional multipart parts, into the request the application forwards to a backend. This can let the attacker add or override form fields (e.g. set `is_admin=true`) seen by the downstream parser. This is an instance of CWE-93 (CRLF injection). The fix escapes CR, LF, and `"` as `%0D`, `%0A`, and `%22` in field names and filenames, matching the serialization browsers use per the WHATWG HTML multipart/form-data encoding algorithm. Exploitation requires the consuming application to use untrusted input as a field name or filename; applications that use only fixed/trusted field names are not affected. Fixed in 2.5.6, 3.0.5, and 4.0.6.
CVSS Score
HIGH
Related Weaknesses (CWE)
References
- https://cwe.mitre.org/data/definitions/93.html
- https://github.com/form-data/form-data/commit/64190db548c0179e37206858e39f27cf51
- https://github.com/form-data/form-data/commit/be3f3cf553978bac15a5182f1f3c3d2d38
- https://github.com/form-data/form-data/commit/c7133499c2ee1b80c678e411244f4442bf
- https://github.com/form-data/form-data/security/advisories/GHSA-hmw2-7cc7-3qxx
- https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#multipar
- https://www.npmjs.com/package/form-data
- https://access.redhat.com/errata/RHSA-2026:33155
- https://access.redhat.com/errata/RHSA-2026:33160
- https://access.redhat.com/errata/RHSA-2026:33163
- https://access.redhat.com/errata/RHSA-2026:33173
- https://access.redhat.com/errata/RHSA-2026:33183
- https://access.redhat.com/errata/RHSA-2026:34342
- https://access.redhat.com/errata/RHSA-2026:36319
- https://access.redhat.com/errata/RHSA-2026:36625
FAQ
What is CVE-2026-12143?
CVE-2026-12143 is a vulnerability with a CVSS score of 7.5 (HIGH). form-data is a library for creating readable multipart/form-data streams. In versions through 4.0.5, the `field` argument to `FormData#append` and the `filename` option are concatenated verbatim into ...
How severe is CVE-2026-12143?
CVE-2026-12143 has been rated HIGH with a CVSS base score of 7.5/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-12143?
Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.