CVE-2026-49756 - Multipart form-data header injection in Req via unescaped name/filename/content_type

CVE-2026-49756 - Multipart form-data header injection in Req via unescaped name/filename/content_type

https://cvefeed.io/rssfeed/latest.atom / Mon, 06/08/2026 - 20:28
CVE ID :CVE-2026-49756
Published : June 8, 2026, 4:16 p.m. | 48 minutes ago
Description :Improper Neutralization of CRLF Sequences ('CRLF Injection') vulnerability in wojtekmach Req allows multipart parameter smuggling via attacker-influenced part metadata. Req.Utils.encode_form_part/2 in lib/req/utils.ex builds the per-part headers by interpolating the caller-supplied name, filename, and content_type values directly into the content-disposition and content-type lines with no escaping or CRLF stripping. A value containing ", \r, or \n closes the surrounding quoted value and starts a new header line; an additional \r\n-- terminates the current part and prepends a smuggled part of the attacker's choosing. This is reachable through every supported way of supplying a part. It is particularly easy when value is a %File.Stream{}, because filename then defaults to Path.basename(stream.path) and POSIX filenames may legitimately contain \r and \n. Any application that forwards user-controlled filenames (or field names / MIME types) through Req.post/2 with form_multipart: lets an attacker inject arbitrary headers into the outgoing multipart body or smuggle additional fields and parts into the request the victim service sends downstream. This issue affects req: from 0.5.3 before 0.6.0.
Severity: 2.1 | LOW
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