Vulnerability · Published Mar 4, 2026 · Assigned by GitHub_M
CVE-2026-28434cpp-httplib's default exception handler leaks e.what() to clients via EXCEPTION_WHAT response header
Medium 5.3
In plain English
A medium-severity information exposure in cpp-httplib from yhirose. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 29% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | cpp-httplib | no fix listed | DEBIAN-CVE-2026-28434 |
| Debian:13 | cpp-httplib | no fix listed | DEBIAN-CVE-2026-28434 |
| Debian:14 | cpp-httplib | 0.41.0+ds-3 | DEBIAN-CVE-2026-28434 |
| Ubuntu:25.10 | cpp-httplib | no fix listed | UBUNTU-CVE-2026-28434 |
| Ubuntu:26.10 | cpp-httplib | no fix listed | UBUNTU-CVE-2026-28434 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| yhirose | cpp-httplib | < 0.35.0 |
Weakness: CWE-200 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N