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CVE-2026-28434— cpp-httplib's default exception handler leaks e.what() to clients via EXCEPTION_WHAT response header

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 0.35.0之前版本存在信息泄露漏洞，该漏洞源于未注册自定义异常处理程序时，内部异常消息会泄露给客户端。

CVSS 5.3 · Medium EPSS 0.43% · P35

Possible ATT&CK Techniques 1 AI

T1530 · Data from Cloud Storage
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I. Basic Information for CVE-2026-28434

Vulnerability Information
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Vulnerability Title
cpp-httplib's default exception handler leaks e.what() to clients via EXCEPTION_WHAT response header
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 0.35.0, when a request handler throws a C++ exception and the application has not registered a custom exception handler via set_exception_handler(), the library catches the exception and writes its message directly into the HTTP response as a header named EXCEPTION_WHAT. This header is sent to whoever made the request, with no authentication check and no special configuration required to trigger it. The behavior is on by default. A developer who does not know to opt in to set_exception_handler() will ship a server that leaks internal exception messages to any client. This vulnerability is fixed in 0.35.0.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
信息暴露
Source: CVE Program / CVE List V5
Vulnerability Title
cpp-httplib 信息泄露漏洞
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 0.35.0之前版本存在信息泄露漏洞，该漏洞源于未注册自定义异常处理程序时，内部异常消息会泄露给客户端。
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 < 0.35.0 -

II. Public POCs for CVE-2026-28434

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III. Intelligence Information for CVE-2026-28434

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Patches & Fixes for CVE-2026-28434 (1)

Vendor Advisories for CVE-2026-28434 (1)

IV. Related Vulnerabilities

Same product: cpp-httplib
Same vendor: yhirose
Same weakness: CWE-200

V. Comments for CVE-2026-28434

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