CVE-2026-33490: low-severity vulnerability in h3js h3
h3: Missing Path Segment Boundary Check in `mount()` Causes Middleware Execution on Unrelated Prefix-Matching Routes
Published
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8Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 3.7epss 0.2%
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.
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
Affected products
h3js · h3Related CVEs — h3js h3
In the same product, most dangerous first.
CVE-2026-23527HIGHh3 v1 has Request Smuggling (TE.TE) issueEPSS 0.6%CVE-2026-86253HIGHh3 before 1.15.6 Path Traversal via Percent-Encoded Dot SegmentsEPSS 0.6%CVE-2026-33128HIGHh3 has a Server-Sent Events Injection via Unsanitized Newlines in Event Stream FieldsEPSS 0.6%CVE-2026-86250HIGHh3 before 2.0.1-rc.18 Denial of Service via Unbounded Chunked CookieEPSS 0.5%CVE-2026-86251HIGHh3 before 1.15.9 Path Traversal via Double DecodingEPSS 0.4%CVE-2026-33131HIGHh3 has a middleware bypass with one gadgetEPSS 0.4%