Vulnerability · Published Jan 1, 2026 · Assigned by GitHub_M
CVE-2026-21428cpp-httplib has CRLF injection in http headers
High 7.7
In plain English
A high-severity security flaw in cpp-httplib from yhirose. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 35% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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 packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | cpp-httplib | no fix listed | DEBIAN-CVE-2026-21428 |
| Debian:13 | cpp-httplib | no fix listed | DEBIAN-CVE-2026-21428 |
| Debian:14 | cpp-httplib | 0.41.0+ds-3 | DEBIAN-CVE-2026-21428 |
| Ubuntu:25.10 | cpp-httplib | no fix listed | UBUNTU-CVE-2026-21428 |
| Ubuntu:26.10 | cpp-httplib | no fix listed | UBUNTU-CVE-2026-21428 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| yhirose | cpp-httplib | < 0.30.0 |
Weakness: CWE-93 · 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