CVE-2026-28434 cpp-httplib's default exception handler leaks e.what() to clients via EXCEPTION_WHAT response header
cpp-httplib leaks internal exception messages to clients via a response header by default, exposing sensitive information to unauthenticated attackers.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-28434?
CVE-2026-28434 is a medium-severity vulnerability in yhirose cpp-httplib, published on 4 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-200
Which versions are affected by CVE-2026-28434?
It affects 1 product.
Products include Yhirose Cpp-Httplib.
How do I fix CVE-2026-28434?
Upgrade to a fixed version.
Is CVE-2026-28434 being exploited?
There is no known exploitation of CVE-2026-28434 in the wild and no public exploit code.
Other vulnerabilities in yhirose cpp-httplib
- CVE-2025-66570 cpp-httplib Untrusted HTTP Header Handling: Internal Header Shadowing (REMOTE*/LOCAL*)
- CVE-2026-45372 cpp-httplib: HTTP header value percent-decoding in server-side `parse_header` enables CRLF injection
- CVE-2026-46527 Null dereference in cpp-httplib
- CVE-2026-32627 cpp-httplib has a Silent TLS Certificate Verification Bypass on HTTPS Redirect via Proxy
- CVE-2026-22776 cpp-httplib vulnerable to a denial of service (DOS) using a zip bomb
Sources
Also known as DEBIAN-CVE-2026-28434, GHSA-8mpw-r4gc-xm7q, UBUNTU-CVE-2026-28434.