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High severity · published Jan 1, 2026
CVE-2026-21428
cpp-httplib has CRLF injection in http headers
7.5
CVSS
0.4%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
High
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.4% · higher than 35% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
CP
cpp-httplib · yhirose
< 0.30.0 · source: vendor, NVD
Affected product
CP
cpp-httplib
yhirose
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-21428
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-21428
Patch
https://github.com/yhirose/cpp-httplib/commit/98048a033a532ff22320ce1d11789f8d5710dfcd
Product
https://github.com/yhirose/cpp-httplib/releases/tag/v0.30.0
Exploit
https://github.com/yhirose/cpp-httplib/security/advisories/GHSA-wpc6-j37r-jcx7
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