TA488 OWAReaper: A "Half-Click" Attack that Adds Persistence Inside OWA Just by Opening an Email

TA488 OWAReaper: A "Half-Click" Attack that Adds Persistence Inside OWA Just by Opening an Email 1. Basic Information Article Name : Cleaning Out Inboxes: TA488 Comes for Outlook with Another Half-Click Exploit Publisher : Proofpoint Threat Insight Publication Date : 2026-07-29 Original Source : https://www.proofpoint.com/us/blog/threat-insight/cleaning-out-inboxes-ta488-comes-outlook-another-half-click-exploit Related Source : https://www.bleepingcomputer.com/news/security/russian-hackers-exploit-exchange-owa-zero-day-for-long-term-mailbox-access/ Related Entities : TA488, Void Blizzard, Laundry Bear, OWAReaper, ZimReaper, CVE-2026-42897, Microsoft Exchange Outlook Web Access Severity : Emergency Target Period : 2026-07-30T08:10:34+09:00 to 2026-07-31T08:06:06+09:00 2. One-Line Summary This is an attack where viewing a crafted email in OWA runs JavaScript, leaves no file on the device, achieves persistence in both the browser and Exchange, and steals saved credentials, OAuth tokens, and mailbox permissions. 3. Attack Flow A compromised account sends a normal informational email with no URLs or attachments. The victim opens the email in the OWA reading pane. CVE-2026-42897 triggers an onload event, and reconstructs Base64 JavaScript from image fragments in the email body. OWAReaper runs in the OWA browser context and deletes the malicious parts from the original email. It collects browser autofill IDs and passwords using an invisible DOM input field. It hides its encrypted self inside OWA settings to run again when OWA syncs and restores. It steals OAuth tokens via a privileged Outlook add-in. It gives Owner permissions to the Default principal on all mail folders, allowing continuous access from another authenticated account in the same organization. It embeds an iframe into the IndexedDB offline mail cache to reinfect it. It receives commands from GitHub commit messages or attacker emails, and sends data through multiple paths. 4. Attacker Position and Execution L