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CVE-2026-46527— cpp-httplib: Malicious `X-Forwarded-For` Under Trusted-Proxy Configuration Triggers Empty `vector::front()`, Leading to Undefined Behavior and Server Crash

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 0.44.0之前版本存在代码问题漏洞，该漏洞源于当服务器设置了非空可信代理列表时，攻击者可发送包含X-Forwarded-For标头的HTTP请求，其值解析为无效IP段，导致对空std::vector调用front()，可能造成进程异常终止。

AI Predicted 5.3 Difficulty: Easy EPSS 0.49% · P40

Affected Version Matrix 1

VendorProduct Version RangeStatus
yhirose cpp-httplib < 0.44.0 affected
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I. Basic Information for CVE-2026-46527

Vulnerability Information
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Vulnerability Title
cpp-httplib: Malicious `X-Forwarded-For` Under Trusted-Proxy Configuration Triggers Empty `vector::front()`, Leading to Undefined Behavior and Server Crash
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 0.44.0, When the server has called Server::set_trusted_proxies() with a non-empty trusted-proxy list, an attacker can send an HTTP request that includes an X-Forwarded-For header whose value parses to no valid IP segments. The code path then executes get_client_ip(), which calls front() on an empty std::vector—undefined behavior in C++. On typical implementations this manifests as abnormal process termination (denial of service). With Sanitizers enabled, you get an explicit runtime diagnostic. This vulnerability is fixed in 0.44.0.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
空指针解引用
Source: CVE Program / CVE List V5
Vulnerability Title
cpp-httplib 代码问题漏洞
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 0.44.0之前版本存在代码问题漏洞，该漏洞源于当服务器设置了非空可信代理列表时，攻击者可发送包含X-Forwarded-For标头的HTTP请求，其值解析为无效IP段，导致对空std::vector调用front()，可能造成进程异常终止。
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 < 0.44.0 -

II. Public POCs for CVE-2026-46527

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III. Intelligence Information for CVE-2026-46527

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Vendor Advisories for CVE-2026-46527 (1)

Same Patch Batch · yhirose · 2026-05-29 · 3 CVEs total

CVE-2026-45372 9.9 CRITICAL cpp-httplib: HTTP header value percent-decoding in server-side `parse_header` enables CRLF
CVE-2026-45352 5.3 MEDIUM cpp-httplib DoS: Negative chunk-size in chunked Transfer-Encoding

IV. Related Vulnerabilities

Same product: cpp-httplib
Same vendor: yhirose
Same weakness: CWE-476

V. Comments for CVE-2026-46527

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