CVE-2026-33490: h3

Medium severity, CVSS 5.3. EPSS: 0.3% chance of exploitation in the next 30 days.

H3 is a minimal H(TTP) framework. In versions 2.0.0-0 through 2.0.1-rc.16, the `mount()` method in h3 uses a simple `startsWith()` check to determine whether incoming requests fall under a mounted sub-application's path prefix. Because this check does not verify a path segment boundary (i.e., that the next character after the base is `/` or end-of-string), middleware registered on a mount like `/admin` will also execute for unrelated routes such as `/admin-public`, `/administrator`, or `/adminstuff`. This allows an attacker to trigger context-setting middleware on paths it was never intended to cover, potentially polluting request context with unintended privilege flags. Version 2.0.2-rc.17 contains a patch.

Affected products

• h3 h3: version 2.0.1 only

Published 2026-03-26. Last modified 2026-06-17.