TA422 Hackers Attack Organizations Using Outlook & WinRAR Vulnerabilities

Hackers exploit Outlook and WinRAR vulnerabilities because these widely used software programs are lucrative targets.

Outlook vulnerabilities offer:-

Access to sensitive emails
Access to sensitive information

WinRAR vulnerabilities provide an entry point to manipulate compressed files, potentially executing malicious code on a victim’s system.

Cybersecurity researchers at Proofpoint recently discovered that the TA422 APT Group is actively exploiting the Outlook and WinRAR vulnerabilities to attack organizations.

Exploiting of Patched Vulnerabilities

Since March 2023, Proofpoint found Russian APT TA422 using patched vulnerabilities to target Europe and North America. The TA422 APT group is linked to the following groups and tied to the Russian GRU by the US Intelligence Community:-

APT28
Forest Blizzard
Pawn Storm
Fancy Bear
BlueDelta

While engaging in typical targeted actions, TA422 showed an unexpected surge in emails exploiting CVE-2023-23397, a Microsoft Outlook vulnerability, sending over 10,000 emails to diverse sectors.

Besides this, the operators of the TA422 APT group also exploited a WinRAR vulnerability, CVE-2023-38831, in their campaigns.

TA422 launched massive campaigns in March 2023, exploiting CVE-2023-23397 against targets in:-

Europe
North America

Earlier, they targeted Ukrainian entities in April 2022 using the same exploit. Proofpoint noticed a significant surge in activity, with over 10,000 attempts to exploit a Microsoft Outlook vulnerability during late summer 2023.

It’s unclear if this was a mistake or a deliberate effort to gather target credentials. TA422 re-targeted higher education and manufacturing users, suggesting these entities are priority targets.

In the late summer campaign, TA422 used an appointment attachment with a fake file extension, leading to an SMB listener on a compromised Ubiquiti router.

This router acted as an NTLM listener, recording inbound credential hashes without extensive network engagement when Outlook processed the attachment.

Late summer 2023 sample of TA422 phishing email. (Source – Proofpoint)

Proofpoint’s tracking of Portugalmail addresses revealed more TA422 activity. In September 2023, TA422 exploited WinRAR vulnerability CVE-2023-32231 in two campaigns, using different Portugalmail addresses and spoofing geopolitical entities.

Emails with BRICS Summit and European Parliament meeting subjects contained RAR attachments dropping a .cmd file.

The file modified proxy settings downloaded a lure document, and connected to an IP-literal Responder server. The server, likely a compromised Fortigate FortiOS Firewall, initiated the NTLM credential exchange.

Lure document from the September 1, 2023 campaign. (Source – Proofpoint)

Between September and November 2023, Proofpoint tracked TA422 campaigns using Portugalmail and Mockbin for redirection.

Mockbin campaign lure documents. (Source – Proofpoint)

Targeting government and defense sectors, TA422 employed Mockbin to lead victims to InfinityFree domains. After browser fingerprinting, victims were directed to InfinityFree, initiating a chain of activity.

Despite the exploitation of disclosed vulnerabilities like CVE-2023-23397 and CVE-2023-38831, TA422 persists, likely relying on unpatched systems for continued success.

IOCs

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