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

Quick assessment

Affected
yhirose cpp-httplib
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

cpp-httplib是yhirose个人开发者的一款使用C++语言编写的HTTP/HTTPS服务器和客户端库。 cpp-httplib 0.30.0之前版本存在注入漏洞，该漏洞源于未检查用户提供标头中的CR和LF字符，可能导致添加额外标头、修改请求主体和触发服务端请求伪造攻击。

AI Predicted 8.1 Difficulty: Easy EPSS 0.41% · P33

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application
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I. Basic Information for CVE-2026-21428

Vulnerability Information
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Vulnerability Title
cpp-httplib has CRLF injection in http headers
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
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
Source: CVE Program / CVE List V5
Vulnerability Type
对CRLF序列的转义处理不恰当(CRLF注入)
Source: CVE Program / CVE List V5
Vulnerability Title
cpp-httplib 注入漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
cpp-httplib是yhirose个人开发者的一款使用C++语言编写的HTTP/HTTPS服务器和客户端库。 cpp-httplib 0.30.0之前版本存在注入漏洞，该漏洞源于未检查用户提供标头中的CR和LF字符，可能导致添加额外标头、修改请求主体和触发服务端请求伪造攻击。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
yhirose cpp-httplib < 0.30.0 -

II. Public POCs for CVE-2026-21428

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III. Intelligence Information for CVE-2026-21428

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Patches & Fixes for CVE-2026-21428 (1)

Vendor Advisories for CVE-2026-21428 (1)

Other References for CVE-2026-21428 (1)

IV. Related Vulnerabilities

Same product: cpp-httplib
Same vendor: yhirose
Same weakness: CWE-93

V. Comments for CVE-2026-21428

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