h3: Missing Path Segment Boundary Check in `mount()` Causes Middleware Execution on Unrelated Prefix-Matching Routes

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Summary

CVECVE-2026-33490
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-03-26 18:16:30 UTC
Updated2026-03-31 21:00:13 UTC
DescriptionH3 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.

Risk And Classification

Primary CVSS: v3.1 5.3 MEDIUM from [email protected]

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

EPSS: 0.000440000 probability, percentile 0.134630000 (date 2026-04-01)

Problem Types: CWE-706 | CWE-706 CWE-706: Use of Incorrectly-Resolved Name or Reference

VersionSourceTypeScoreSeverityVector
3.1[email protected]Primary5.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
3.1[email protected]Secondary3.7LOWCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
3.1CNADECLARED3.7LOWCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Application H3 H3 2.0.1 rc1 All All
Application H3 H3 2.0.1 rc10 All All
Application H3 H3 2.0.1 rc11 All All
Application H3 H3 2.0.1 rc12 All All
Application H3 H3 2.0.1 rc13 All All
Application H3 H3 2.0.1 rc14 All All
Application H3 H3 2.0.1 rc15 All All
Application H3 H3 2.0.1 rc16 All All
Application H3 H3 2.0.1 rc2 All All
Application H3 H3 2.0.1 rc3 All All
Application H3 H3 2.0.1 rc4 All All
Application H3 H3 2.0.1 rc5 All All
Application H3 H3 2.0.1 rc6 All All
Application H3 H3 2.0.1 rc7 All All
Application H3 H3 2.0.1 rc8 All All
Application H3 H3 2.0.1 rc9 All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA H3js H3 affected >= 2.0.1-alpha.0, < 2.0.1-rc.17 Not specified

References

ReferenceSourceLinkTags
github.com/h3js/h3/security/advisories/GHSA-2j6q-whv2-gh6w 134c704f-9b21-4f2e-91b3-4a467353bcc0 github.com Exploit, Mitigation, Vendor Advisory
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis
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