CVE-2026-86205 PUBLISHED

h3 before 2.0.1-rc.18 Open Redirect via redirectBack()

Assigner: VulnCheck
Reserved: 05.09.2026 Published: 06.09.2026 Updated: 06.09.2026

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.

CVSS Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N
CVSS Score: 5.3

Exploitability Metrics		Vulnerable System Impact Metrics		Subsequent System Impact Metrics
Attack Vector	Network	Confidentiality	Low	Confidentiality	None
Attack Complexity	Low	Integrity	Low	Integrity	None
Attack Requirements	None	Availability	None	Availability	None
Privileges Required	None
User Interaction	Passive

CVSS 4.0

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N
CVSS Score: 5.4

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

CVSS 3.1

Product Status

Vendor	h3js
Product	h3
Versions	Default: unaffected affected from 2.0.1-rc.17 to 2.0.1-rc.18 (excl.) Version 2.0.1-rc.18 is unaffected

CVE-2026-86205 PUBLISHED

h3 before 2.0.1-rc.18 Open Redirect via redirectBack()

Metrics

Product Status

Credits

References

Problem Types