CVE-2026-49756

Summary

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–<boundary> 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.

Affected Software

VendorProductVersion RangeStatus
wojtekmachreq0.5.3 < 0.6.0affected
wojtekmachreq60253dbe9436cb8e9c738f895032f2e87939b597 < 74506ff2c5addf74df85d79dc726e9b2e264a8baaffected

Weaknesses

  • CWE-93: CWE-93 Improper Neutralization of CRLF Sequences ('CRLF Injection')

Workarounds

Sanitize attacker-influenced name, filename, and content_type values before passing them to Req.post/2 with form_multipart:. At minimum, reject (or strip) any value containing \r, \n, or ". When forwarding uploads, derive filename from a normalised string rather than Path.basename/1 on a user-controlled path.

ADP Enrichment

CISA ADP Vulnrichment

  • SSVC:
  • Exploitation: poc
    • Automatable: no
    • Technical Impact: partial

Additional References

References