CVE-2026-12143 form-data does not escape CR/LF/quote in multipart field names and filenames (CRLF injection)
Attackers can inject headers or smuggle parts via unescaped field names in form-data, potentially modifying downstream form data.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-12143?
CVE-2026-12143 is a high-severity vulnerability in form-data, published on 12 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-93
Which versions are affected by CVE-2026-12143?
6 open source packages ship an affected version, including form-data.
| Package | Affected | Fixed in |
|---|---|---|
form-data npm | All versions | 2.5.6 |
form-data npm | All versions | 2.5.6 |
form-data npm | From 3.0.0 | 3.0.5 |
form-data npm | From 3.0.0 | 3.0.5 |
form-data npm | From 4.0.0 | 4.0.6 |
form-data npm | From 4.0.0 | 4.0.6 |
How do I fix CVE-2026-12143?
Upgrade form-data to a fixed version for your release line: 2.5.6, 3.0.5 or 4.0.6.
Is CVE-2026-12143 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-12143 exists.
Sources
Also known as AZL-90099, CLEANSTART-2026-FQ89941, CLEANSTART-2026-JF12177, CLEANSTART-2026-OW89546, CLSA-2026-1784856187, CLSA-2026-1784856461 and 57 more.