CVE-2026-21428 HIGH

CVE-2026-21428: cpp-httplib has CRLF injection in http headers

Vendor Yhirose
Product cpp-httplib
Weakness CWE-93 · CRLF injection
Published January 1, 2026
Last update January 2, 2026
View on NVD All CVEs

CVSS base score

7.7/10
Attack vector Network
Attack complexity Low
Privileges required None
User interaction None
Confidentiality —
Integrity —

CVSS 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

What the vulnerability does

01Description

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.

Key dates

02Disclosure timeline

January 1, 2026 CVE published
January 2, 2026 Record updated