Open Redirect Vulnerability in h3 Framework Prior to 2.0.1-rc.18
CVE-2026-86205

5.3MEDIUM

Key Information:

Vendor

H3js

Status
H3
Vendor
CVE Published:
6 September 2026

What is CVE-2026-86205?

The h3 framework versions prior to 2.0.1-rc.18 are susceptible to an open redirect vulnerability in the redirectBack() utility function. This flaw arises from improper sanitization of protocol-relative paths in the Referer header, allowing attackers to construct a same-origin URL with a double-slash path segment. Such crafted URLs can pass origin validation yet result in a Location header that directs users to an external domain, posing significant risks for redirection attacks. Developers are urged to update to the latest version to mitigate this vulnerability.

Affected Version(s)

h3 2.0.1-rc.17 < 2.0.1-rc.18

h3 2.0.1-rc.18

References

https://github.com/h3js/h3/security/advisories/GHSA-fp4x-...
vendor-advisory
https://www.vulncheck.com/advisories/h3-before-2.0.1-rc.1...
third-party-advisory

CVSS V4

Score:
5.3
Severity:
MEDIUM
Confidentiality:
Low
Integrity:
Low
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Attack Required:
None
Privileges Required:
Undefined
User Interaction:
Unknown

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

offset
.