# CVE-2026-21428

## Summary

- **CVE ID:** CVE-2026-21428
- **Severity:** HIGH
- **CVSS Score:** 7.7 (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)
- **CWE:** CWE-93
- **Published:** Jan 1, 2026
- **Last Modified:** Mar 12, 2026

## 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 (< 0.30.0)

## References

- [CNA](https://github.com/yhirose/cpp-httplib/security/advisories/GHSA-wpc6-j37r-jcx7)
- [CNA](https://github.com/yhirose/cpp-httplib/commit/98048a033a532ff22320ce1d11789f8d5710dfcd)
- [CNA](https://github.com/yhirose/cpp-httplib/releases/tag/v0.30.0)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.41%
- **EPSS Percentile:** 34.8

---
_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-11._