CVE-2026-49756 (GCVE-0-2026-49756)

Vulnerability from cvelistv5 – Published: 2026-06-08 15:20 – Updated: 2026-06-08 16:34
VLAI
Title
Multipart form-data header injection in Req via unescaped name/filename/content_type
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.
Severity
2.1 (Low)
CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N
SSVC
Exploitation: poc Automatable: no Technical Impact: partial
CISA Coordinator (v2.0.3)
CWE
  • CWE-93 - Improper Neutralization of CRLF Sequences ('CRLF Injection')
Assigner
EEF
References
Impacted products
Vendor Product Version
wojtekmach req Affected: 0.5.3 , < 0.6.0 (semver)
    cpe:2.3:a:wojtekmach:req:*:*:*:*:*:*:*:*
 Create a notification for this product.
wojtekmach req Affected: 60253dbe9436cb8e9c738f895032f2e87939b597 , < 74506ff2c5addf74df85d79dc726e9b2e264a8ba (git)
    cpe:2.3:a:wojtekmach:req:*:*:*:*:*:*:*:*
 Create a notification for this product.
Credits
Peter Ullrich Wojtek Mach Jonatan Männchen / EEF
Show details on NVD website
To clipboard 

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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.\", \"supportingMedia\": [{\"type\": \"text/html\", \"value\": \"\u003cp\u003eSanitize attacker-influenced \u003ctt\u003ename\u003c/tt\u003e, \u003ctt\u003efilename\u003c/tt\u003e, and \u003ctt\u003econtent_type\u003c/tt\u003e values before passing them to \u003ctt\u003e\u0027Elixir.Req\u0027:post/2\u003c/tt\u003e with \u003ctt\u003eform_multipart:\u003c/tt\u003e. At minimum, reject (or strip) any value containing \u003ctt\u003e\\\\r\u003c/tt\u003e, \u003ctt\u003e\\\\n\u003c/tt\u003e, or \u003ctt\u003e\\\"\u003c/tt\u003e. When forwarding uploads, derive \u003ctt\u003efilename\u003c/tt\u003e from a normalised string rather than \u003ctt\u003ePath.basename/1\u003c/tt\u003e on a user-controlled path.\u003c/p\u003e\", \"base64\": false}]}], \"x_generator\": {\"engine\": \"cvelib 1.8.0\"}, \"descriptions\": [{\"lang\": \"en\", \"value\": \"Improper Neutralization of CRLF Sequences (\u0027CRLF Injection\u0027) vulnerability in wojtekmach Req allows multipart parameter smuggling via attacker-influenced part metadata.\\n\\nReq.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--\u003cboundary\u003e terminates the current part and prepends a smuggled part of the attacker\u0027s choosing.\\n\\nThis 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.\\n\\nThis issue affects req: from 0.5.3 before 0.6.0.\", \"supportingMedia\": [{\"type\": \"text/html\", \"value\": \"Improper Neutralization of CRLF Sequences (\u0027CRLF Injection\u0027) vulnerability in wojtekmach Req allows multipart parameter smuggling via attacker-influenced part metadata.\u003cp\u003e\u003ctt\u003e\u0027Elixir.Req.Utils\u0027:encode_form_part/2\u003c/tt\u003e in \u003ctt\u003elib/req/utils.ex\u003c/tt\u003e builds the per-part headers by interpolating the caller-supplied \u003ctt\u003ename\u003c/tt\u003e, \u003ctt\u003efilename\u003c/tt\u003e, and \u003ctt\u003econtent_type\u003c/tt\u003e values directly into the \u003ctt\u003econtent-disposition\u003c/tt\u003e and \u003ctt\u003econtent-type\u003c/tt\u003e lines with no escaping or CRLF stripping. A value containing \u003ctt\u003e\\\"\u003c/tt\u003e, \u003ctt\u003e\\\\r\u003c/tt\u003e, or \u003ctt\u003e\\\\n\u003c/tt\u003e closes the surrounding quoted value and starts a new header line; an additional \u003ctt\u003e\\\\r\\\\n--\u0026lt;boundary\u0026gt;\u003c/tt\u003e terminates the current part and prepends a smuggled part of the attacker\u0027s choosing.\u003c/p\u003e\u003cp\u003eThis is reachable through every supported way of supplying a part. It is particularly easy when \u003ctt\u003evalue\u003c/tt\u003e is a \u003ctt\u003e%File.Stream{}\u003c/tt\u003e, because \u003ctt\u003efilename\u003c/tt\u003e then defaults to \u003ctt\u003ePath.basename(stream.path)\u003c/tt\u003e and POSIX filenames may legitimately contain \u003ctt\u003e\\\\r\u003c/tt\u003e and \u003ctt\u003e\\\\n\u003c/tt\u003e. Any application that forwards user-controlled filenames (or field names / MIME types) through \u003ctt\u003e\u0027Elixir.Req\u0027:post/2\u003c/tt\u003e with \u003ctt\u003eform_multipart:\u003c/tt\u003e 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.\u003c/p\u003e\u003cp\u003eThis issue affects req: from 0.5.3 before 0.6.0.\u003c/p\u003e\", \"base64\": false}]}], \"problemTypes\": [{\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-93\", \"description\": \"CWE-93 Improper Neutralization of CRLF Sequences (\u0027CRLF Injection\u0027)\"}]}], \"cpeApplicability\": [{\"nodes\": [{\"negate\": false, \"cpeMatch\": [{\"criteria\": \"cpe:2.3:a:wojtekmach:req:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"0.6.0\", \"versionStartIncluding\": \"0.5.3\"}], \"operator\": \"OR\"}], \"operator\": \"AND\"}], \"providerMetadata\": {\"orgId\": \"6b3ad84c-e1a6-4bf7-a703-f496b71e49db\", \"shortName\": \"EEF\", \"dateUpdated\": \"2026-06-08T16:34:58.505Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2026-49756\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-06-08T16:34:58.505Z\", \"dateReserved\": \"2026-06-01T13:45:22.448Z\", \"assignerOrgId\": \"6b3ad84c-e1a6-4bf7-a703-f496b71e49db\", \"datePublished\": \"2026-06-08T15:20:24.035Z\", \"assignerShortName\": \"EEF\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}


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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.