CVE-2026-49756: Improper Neutralization of CRLF Sequences ('CRLF Injection') vulnerability in wojtekmach Req allows multipart parameter smuggling via attacker-influen...

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--<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.

Metrics

CVSS 4.0

2.1/10

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

EPSS Probability

0.18%

7.6th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-93

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

Vendor	Product	Versions
wojtekmach	req	>= 0.5.3, < 0.6.0
wojtekmach	req	>= 60253dbe9436cb8e9c738f895032f2e87939b597, < 74506ff2c5addf74df85d79dc726e9b2e264a8ba

References

Timeline

Published: Jun 8, 2026
Last Modified: Jul 23, 2026
Status: Awaiting Analysis

Frequently Asked Questions

What is CVE-2026-49756?

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.

How severe is CVE-2026-49756?

CVE-2026-49756 has a CVSS score of 2.1/10 (LOW severity). The EPSS model estimates a 0.18% probability of exploitation in the next 30 days.

How do I fix CVE-2026-49756?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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