CVE-2026-12143

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.

How to fix CVE-2026-12143

To remediate CVE-2026-12143, upgrade the affected package to a fixed version below.

• —no fix listed
• —upgrade to 2.5.6 or later

Is CVE-2026-12143 being exploited?

No exploitation signal available. Neither CISA KEV nor a current EPSS score has been published for CVE-2026-12143.

Affected packages (2)

• from 0
• from 0, < 2.5.6

CVSS scores

References (9)

• ADVISORYnvd.nist.gov/vuln/detail/CVE-2026-12143
• ADVISORYsecurity-tracker.debian.org/tracker/CVE-2026-12143
• PATCHgithub.com/form-data/form-data
• WEBgithub.com/form-data/form-data/commit/64190db548c0179e37206858e39f27cf513e9435