cpp-httplib is a C++11 single-file header-only cross platform HTTP/HTTPS library. Prior to version 0.30.0, the ``write_headers`` function does not check for CR & LF characters in user supplied headers, allowing untrusted header value to escape header lines.
This vulnerability allows attackers to add extra headers, modify request body unexpectedly & trigger an SSRF attack. When combined with a server that supports http1.1 pipelining (springboot, python twisted etc), this can be used for server side request forgery (SSRF). Version 0.30.0 fixes this issue.

Metrics

Attack Vector Network

Attack Complexity Low

Privileges Required None

Attack Requirements None

User Interaction None

Vulnerable System Confidentiality Impact None

Vulnerable System Integrity Impact High

Vulnerable System Availability Impact None

Subsequent System Confidentiality Impact None

Subsequent System Integrity Impact None

Subsequent System Availability Impact None

Attack Vector Network

Attack Complexity High

Privileges Required None

Scope Changed

Confidentiality Impact High

Integrity Impact High

Availability Impact None

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

The EPSS score is 0.00045.

Exploitation poc

Automatable yes

Technical Impact partial

Affected Vendors & Products

No data.

No data.

No data.

No data.

Advisories

No advisories yet.

Fixes

Solution

No solution given by the vendor.

Workaround

No workaround given by the vendor.

References
Link Providers
https://github.com/yhirose/cpp-httplib/commit/98048a033a532ff22320ce1d11789f8d5710dfcd cve-icon cve-icon cve-icon
https://github.com/yhirose/cpp-httplib/releases/tag/v0.30.0 cve-icon cve-icon cve-icon
https://github.com/yhirose/cpp-httplib/security/advisories/GHSA-wpc6-j37r-jcx7 cve-icon cve-icon cve-icon
https://nvd.nist.gov/vuln/detail/CVE-2026-21428 cve-icon
https://www.cve.org/CVERecord?id=CVE-2026-21428 cve-icon
History

Fri, 02 Jan 2026 19:15:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Fri, 02 Jan 2026 00:15:00 +0000

Type Values Removed Values Added
References
Metrics threat_severity

None

 cvssV3_1

{'score': 8.7, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N'}

threat_severity

Important

Thu, 01 Jan 2026 18:00:00 +0000

Type Values Removed Values Added
Description cpp-httplib is a C++11 single-file header-only cross platform HTTP/HTTPS library. Prior to version 0.30.0, the ``write_headers`` function does not check for CR & LF characters in user supplied headers, allowing untrusted header value to escape header lines. This vulnerability allows attackers to add extra headers, modify request body unexpectedly & trigger an SSRF attack. When combined with a server that supports http1.1 pipelining (springboot, python twisted etc), this can be used for server side request forgery (SSRF). Version 0.30.0 fixes this issue.
Title cpp-httplib has CRLF injection in http headers
Weaknesses CWE-93
References
Metrics cvssV4_0

{'score': 7.7, 'vector': 'CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:P'}

Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2026-01-02T18:50:20.380Z

Reserved: 2025-12-29T03:00:29.274Z

Link: CVE-2026-21428

cve-icon Vulnrichment

Updated: 2026-01-02T18:50:14.604Z

cve-icon NVD

Status : Awaiting Analysis

Published: 2026-01-01T18:15:41.057

Modified: 2026-01-02T16:45:26.640

Link: CVE-2026-21428

cve-icon Redhat

Severity : Important

Publid Date: 2026-01-01T17:54:43Z

Links: CVE-2026-21428 - Bugzilla

cve-icon OpenCVE Enrichment

No data.

Weaknesses