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CVE-2026-34441: cpp-httplib: HTTP Request Smuggling via Unconsumed GET Request Body

• Severity: medium (CVSS 6.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-03-31 · updated 2026-07-24
• Weakness: CWE-444

Description

cpp-httplib is a C++11 single-file header-only cross platform HTTP/HTTPS library. Prior to version 0.40.0, cpp-httplib is vulnerable to HTTP Request Smuggling. The server's static file handler serves GET responses without consuming the request body. On HTTP/1.1 keep-alive connections, the unread body bytes remain on the TCP stream and are interpreted as the start of a new HTTP request. An attacker can embed an arbitrary HTTP request inside the body of a GET request, which the server processes as a separate request. This issue has been patched in version 0.40.0.

Affected products

• yhirose cpp-httplib: before 0.40.0 — fixed in 0.40.0

How to fix

Upgrade to a fixed version: yhirose cpp-httplib 0.40.0. Check the vendor advisory for mitigations.

References

• https://github.com/yhirose/cpp-httplib/releases/tag/v0.40.0
• https://github.com/yhirose/cpp-httplib/security/advisories/GHSA-jv63-rm9j-6jwc

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