CVE-2026-33490Public exploitNetwork attack vector

Context pollution via mount prefix confusion

Published Mar 26, 2026 · Updated Mar 26, 2026

Path-boundary confusion in H3 2.0.1-alpha.0 through 2.0.1-rc.16 allows remote attackers to pollute request context via crafted paths. The mount() method treats any pathname beginning with a mounted base as in scope, so peer routes such as /admin-public run the mounted middleware; withoutBase() similarly strips coincidental prefixes. Exploitation requires a peer route that shares the base prefix and trusts middleware-set context, enabling authorization bypass or other unintended state changes.

CVSS severity3.7
Low
EPSS probability0.24%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Path-boundary confusion in H3 2.0.1-alpha.0 through 2.0.1-rc.16 allows remote attackers to pollute request context via crafted paths. The mount() method treats any pathname beginning with a mounted base as in scope, so peer routes such as /admin-public run the mounted middleware; withoutBase() similarly strips coincidental prefixes. Exploitation requires a peer route that shares the base prefix and trusts middleware-set context, enabling authorization bypass or other unintended state changes.

The record

CVE
CVE-2026-33490
Published
Mar 26, 2026
Updated
Mar 26, 2026
Vendor
UnJS
Product
H3
Classifications
CWE-706, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 26, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 26, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=>= 2.0.1-alpha.0, < 2.0.1-rc.17

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

UnJS · H3version=>= 2.0.1-alpha.0, < 2.0.1-rc.17

Published CVSS scores

3.7GitHub, Inc.CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
5.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-706Use of Incorrectly-Resolved Name or Reference
T1190Exploit Public-Facing Application

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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