CVE-2026-86205Public exploitNetwork attack vector

Unauthenticated open redirect via protocol-relative Referer path

Published Sep 6, 2026 · Updated Sep 8, 2026

Open redirect in redirectBack() in h3js h3 2.0.1-rc.17 allows remote attackers to send users to external domains through a crafted Referer. The utility accepts a same-origin Referer pathname beginning with double slashes and writes it unchanged to the Location header, which browsers treat as a protocol-relative external URL. Exploitation requires an endpoint using redirectBack() and user navigation from the crafted same-origin path; the redirect can support phishing or OAuth code theft.

CVSS severity5.4
Medium
EPSS probability0.20%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Open redirect in redirectBack() in h3js h3 2.0.1-rc.17 allows remote attackers to send users to external domains through a crafted Referer. The utility accepts a same-origin Referer pathname beginning with double slashes and writes it unchanged to the Location header, which browsers treat as a protocol-relative external URL. Exploitation requires an endpoint using redirectBack() and user navigation from the crafted same-origin path; the redirect can support phishing or OAuth code theft.

The record

CVE
CVE-2026-86205
Published
Sep 6, 2026
Updated
Sep 8, 2026
Vendor
Uber
Product
H3
Classifications
CWE-601, CAPEC-178, T1204.001
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 6, 2026CVE publishedPublication date reported by the CVE source.
  2. Sep 8, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=2.0.1-rc.17 <2.0.1-rc.18

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Uber · H3version=2.0.1-rc.17 <2.0.1-rc.18

Published CVSS scores

5.4GitHub Security AdvisoryCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/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-601URL Redirection to Untrusted Site ('Open Redirect')
CAPEC-178Cross-Site Flashing
T1204.001Malicious Link

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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