What is CVE-2026-86205?

CVE-2026-86205 is a medium-severity vulnerability in H3js H3, classified under URL Redirection to Untrusted Site (Open Redirect). CVSS score: 5.4/10. Published 2026-09-06.

How severe is CVE-2026-86205?

Medium severity. CVSS v3 base score is 5.4 out of 10.

Open Redirect in H3js H3

CVE-2026-86205

h3 versions before 2.0.1-rc.18 contain an open redirect vulnerability in the redirectBack() utility that fails to sanitize protocol-relative paths in the Referer header pathname. Attackers can craft a same-origin URL with a double-slash path segment that passes origin validation but produces a Location header interpreted by browsers as a protocol-relative redirect to an external domain.

Vulnerability class: Open Redirect

CVSS v3 metric

CVSS v3 base score 5.4 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N.

Affected products

H3js H3

Weakness classification (CWE)

CWE-601 — URL Redirection to Untrusted Site (Open Redirect)

References

disclosure@vulncheck.com (vendor-advisory)
disclosure@vulncheck.com (third-party-advisory)

Frequently asked questions

What is CVE-2026-86205?: CVE-2026-86205 is a medium-severity vulnerability in H3js H3, classified under URL Redirection to Untrusted Site (Open Redirect). CVSS score: 5.4/10. Published 2026-09-06.
How severe is CVE-2026-86205?: Medium severity. CVSS v3 base score is 5.4 out of 10.