# CVE-2026-21428: cpp-httplib: cpp-httplib is a C++11 single-file header-only cross platform HTTP/HTTPS library

CVE-2026-21428 is fixed in cpp-httplib on 1 platform by DEBIAN-CVE-2026-21428 (version 0.41.0+ds-3), released January 1, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-21428
- Priority: High
- CVSS: 7.5 (high)
- EPSS: 0.0040
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jan 1, 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | cpp-httplib Debian 14 | 0.41.0+ds-3 | [DEBIAN-CVE-2026-21428](https://patchblox.com/security/data/fix/linux/debian-cve-2026-21428.md) | Jan 1, 2026 |

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Data as of 2026-11-09T01:18:40Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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