What’s Vulnerable › Vulnerabilities

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

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-01-01 · updated 2026-06-17
• Weakness: CWE-93

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.

Affected products

• yhirose cpp-httplib: before 0.30.0 — fixed in 0.30.0

How to fix

Upgrade to a fixed version: yhirose cpp-httplib 0.30.0. Check the vendor advisory for mitigations.

References

• https://github.com/yhirose/cpp-httplib/commit/98048a033a532ff22320ce1d11789f8d5710dfcd
• https://github.com/yhirose/cpp-httplib/releases/tag/v0.30.0
• https://github.com/yhirose/cpp-httplib/security/advisories/GHSA-wpc6-j37r-jcx7

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