CVE-2026-49756Public exploit

Multipart part smuggling via unescaped header metadata

Published Jun 8, 2026 · Updated Jun 8, 2026

CRLF injection in Req 0.5.3 through 0.5.18 allows attackers to smuggle multipart fields through attacker-influenced part metadata. Req.Utils.encode_form_part/2 inserts name, filename, and content_type verbatim into Content-Disposition and Content-Type lines without quote escaping or CRLF stripping. Applications must pass untrusted part metadata to form_multipart; crafted values then inject headers or prepend fields and parts to downstream requests.

CVSS severity2.1
Low
EPSS probability0.21%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

CRLF injection in Req 0.5.3 through 0.5.18 allows attackers to smuggle multipart fields through attacker-influenced part metadata. Req.Utils.encode_form_part/2 inserts name, filename, and content_type verbatim into Content-Disposition and Content-Type lines without quote escaping or CRLF stripping. Applications must pass untrusted part metadata to form_multipart; crafted values then inject headers or prepend fields and parts to downstream requests.

The record

CVE
CVE-2026-49756
Published
Jun 8, 2026
Updated
Jun 8, 2026
Vendor
Wojtek Mach
Product
Req
Classifications
CWE-93, CAPEC-33, CAPEC-105
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 8, 2026CVE publishedPublication date reported by the CVE source.
  2. Jun 8, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0.5.3 <0.6.0
  2. Affected versionversion=60253dbe9436cb8e9c738f895032f2e87939b597 <74506ff2c5addf74df85d79dc726e9b2e264a8ba

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

Wojtek Mach · Reqversion=0.5.3 <0.6.0; version=60253dbe9436cb8e9c738f895032f2e87939b597 <74506ff2c5addf74df85d79dc726e9b2e264a8ba

Published CVSS scores

2.1Erlang Ecosystem FoundationCVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N
3.7NIST National Vulnerability DatabaseCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-93Improper Neutralization of CRLF Sequences ('CRLF Injection')
CAPEC-33HTTP Request Smuggling
CAPEC-105HTTP Request Splitting

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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