Agora Project CVE-2026-63169

Requires an authenticated Agora Project account (PR:L) with permission to post messages into a channel; the attacker must share that channel with intended victims. Exploitation flows specifically through the messenger feature's HTMLPurifier SafeIframe handling, which permits attacker-controlled iframe markup. No victim interaction beyond viewing the channel is needed (UI:N) because stored messages are automatically rendered to other members, enabling zero-click execution. Limiting factors: valid authentication is mandatory, exploitation is scoped to users who are members of the same channel, and instances upgraded to 26.10.0 or later are not affected.

This is a medium-severity stored XSS (CVSS 4.0 base 5.3, CWE-79) in the Agora Project messenger, and the real-world priority is moderate rather than urgent. The provided CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:L/UI:N) shows a network-reachable, low-complexity flaw that requires authentication (PR:L) but no victim interaction (UI:N) because the malicious iframe is auto-rendered to channel members - this zero-click delivery is the main risk amplifier. Impact is deliberately scored low: all vulnerable-system impacts are N and only subsequent-system confidentiality/integrity are Low (SC:L/SI:L), reflecting script execution confined to recipients' browser context rather than server compromise. No EPSS score, no CISA KEV listing, and no POC were provided, so there is no public exploit identified at time of analysis and no evidence of active exploitation; the lack of an EPSS value means exploitation probability cannot be quantified from the input. The dominant limiting factor is the authentication requirement - an attacker needs a valid account and shared channel, making this most relevant as an insider/post-compromise or multi-tenant abuse vector rather than an internet-wide drive-by. Net: a legitimate but not emergency-grade issue; patch during normal cycles.

An authenticated user with access to a channel posts a message containing a crafted iframe that slips through HTMLPurifier's SafeIframe allowance in the messenger. When other channel members simply open the conversation, the iframe renders automatically with no clicks required, triggering a drive-by download or executing attacker-framed JavaScript in each victim's browser session. No public exploit code was identified in the provided data.