VulnerabilityPublished 26 Mar 2026

CVE-2026-33490: h3js h3 · Use of Incorrectly-Resolved Name or Reference

Affects h3js h3Source CVE Database V5

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Not known to be exploited · CVSS 3.7 Low : upgrade to 2.0.1-rc.17 when convenient.

Data as of 30 Oct 2026, 11:52 UTC

CVSS 3.1 base score

3.7Low

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.2% chance of exploitation in 30 days – higher than 16% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 2.0.1-rc.17

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

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

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: High: A successful attack depends on conditions beyond the attacker's control. That is, a successful attack cannot be accomplished at will, but requires the attacker to invest in some measurable amount of effort in preparation or execution against the vulnerable component before a successful attack can be expected. For example, a successful attack may require an attacker to: gather knowledge about the environment in which the vulnerable target/component exists; prepare the target environment to improve exploit reliability; or inject themselves into the logical network path between the target and the resource requested by the victim in order to read and/or modify network communications (e.g., a man in the middle attack).
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 26 Mar 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 30 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade h3js h3 to 2.0.1-rc.17.

Affected software

Product	Affected	Fixed in
h3jsh3	Affected >=2.0.1-alpha.0 <2.0.1-rc.17	Fixed in 2.0.1-rc.17
GitHubh3js/h3`pkg:github/h3js/h3`Other threats	Affected =2.0.2-rc.17	Fixed in–

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

To mitigate this vulnerability, organizations should upgrade all instances of h3js to version 2.0.2-rc.17 or later, where the patch correctly verifies path segment boundaries in the mount() method. Until upgrading is possible, developers should review and refactor middleware mounting logic to ensure explicit path segment checks are implemented, such as verifying that the character following the prefix is either a slash ('/') or the end of the string. Application code can implement custom middleware wrappers to enforce stricter path matching rules. Additionally, thorough testing of route matching and middleware execution paths should be conducted to detect unintended middleware invocation. Monitoring and logging of unusual access patterns to administrative or privileged routes can help detect exploitation attempts. Finally, applying the principle of least privilege in middleware design and minimizing privilege flags set in request contexts reduces the potential impact of this vulnerability.

Description

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.

Impact

The primary impact of this vulnerability is the potential for privilege pollution within applications using the affected h3js versions. Middleware intended to protect or modify requests under specific path prefixes may inadvertently execute on unrelated paths, potentially granting unauthorized privileges or altering request context inappropriately. This can lead to logical flaws, unauthorized access to privileged functionality, or bypass of intended access controls. While it does not directly expose sensitive data or cause service disruption, the integrity of application security controls is compromised. Organizations relying on h3js for routing and middleware management in web applications could face increased risk of privilege escalation attacks or unauthorized feature access. The impact is more significant in applications with sensitive administrative or restricted routes mounted via h3's mount() method. Since exploitation requires no authentication or user interaction, attackers can probe and exploit this flaw remotely. However, the overall risk is mitigated by the need for specific middleware configurations and the limited scope of the vulnerability.

CWE-706Use of Incorrectly-Resolved Name or Reference (opens in a new tab)
Class weaknessOWASP Top 10 A01:2021: Broken Access Control (opens in a new tab)
The product uses a name or reference to access a resource, but the name/reference resolves to a resource that is outside of the intended control sphere.
Attack patterns
Redirect Access to Libraries (opens in a new tab)
Create files with the same name as files protected with a higher classification (opens in a new tab)
Passing Local Filenames to Functions That Expect a URL (opens in a new tab)
DLL Side-Loading (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

github.com/h3js/h3/security/advisories/GHSA-2j6q-whv2-gh6w (opens in a new tab)

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 26 Mar 2026, 18:01 UTC

WeaknessesCWE-706

Technical details

References

Community reviews

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