Vulnerability in Yhirose Cpp-Httplib
CVE-2026-21428
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.
Vulnerability class: CRLF Injection
EPSS: 0.004 (34.5th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N.
Affected products
- Yhirose Cpp-httplib — versions < 0.30.0
Weakness classification (CWE)
References
- security-advisories@github.com (x_refsource_CONFIRM, Exploit, Third Party Advisory)
- security-advisories@github.com (Patch, x_refsource_MISC)
- security-advisories@github.com (Product, x_refsource_MISC, Release Notes)
Frequently asked questions
- What is CVE-2026-21428?
- CVE-2026-21428 is a high-severity vulnerability in Yhirose Cpp-Httplib, classified under CRLF Injection. CVSS score: 7.5/10. Published 2026-01-01.
- How severe is CVE-2026-21428?
- High severity. CVSS v3 base score is 7.5 out of 10.