An authorization bypass allowing users with only read permissions to pin or unpin messages in Open WebUI. The pin_channel_message endpoint performs a write operation that changes a message's pinned status, pinned_by and pinned_at fields, but the checks performed on that endpoint only verify read access. This permits a user who normally has no modification rights to manipulate message metadata, which can interfere with message ordering and potentially expose the user to misinformation or confusion. The weakness is classified as CWE‑639.

Open WebUI installations running a version before 0.9.5 are affected. The platform is a self‑hosted, offline artificial intelligence interface that supports collaborative channels.

The CVSS score of 4.3 signals a moderate risk level, and the vulnerability is not listed in the CISA KEV catalog. No EPSS score is available, so the current estimate of exploitation probability is unknown. The attack likely involves legitimate users or compromised read‑only accounts accessing the public API or WebUI, enabling them to send pin or unpin requests. No special privileges are required beyond legitimate usage of the application. The impact is limited to post‑moderation manipulation and does not grant arbitrary code execution or full data exfiltration.