Authorization bypass through user-controlled key in Discourse - #VU165850
Published: November 11, 2026
Vulnerability identifier: #VU165850
CSH Severity: Low
CVSS v4: 6.9 [CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N]
CVE-ID: N/A
CWE-ID: CWE-639
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote privileged user to download secure uploads belonging to another site in a Discourse multisite cluster.
The vulnerability exists due to authorization bypass through a user-controlled key in secure upload signing when multisite sites share one S3 bucket. A remote privileged user can obtain signed access to another site's secure uploads to disclose sensitive information across site boundaries.
Affected software
Discourse
Remediation
Install security update from vendor's website.
Discourse - addressed in versions 2026.7.5, 2026.9.2, 2026.10.1