Chinese Hackers Exploited New Zero-Day in Barracuda’s ESG Appliances

Barracuda has revealed that Chinese threat actors exploited a new zero-day in its Email Security Gateway (ESG) appliances to deploy backdoors on a “limited number” of devices.

Tracked as CVE-2023-7102, the issue relates to a case of arbitrary code execution that resides within a third-party and open-source library Spreadsheet::ParseExcel that’s used by the Amavis scanner within the gateway.

The company attributed the activity to a threat actor tracked by Google-owned Mandiant as UNC4841, which was previously linked to the active exploitation of another zero-day in Barracuda devices (CVE-2023-2868, CVSS score: 9.8) earlier this year.

Successful exploitation of the new flaw is accomplished by means of a specially crafted Microsoft Excel email attachment. This is followed by the deployment of new variants of known implants called SEASPY and SALTWATER that are equipped to offer persistence and command execution capabilities.

Barracuda said it released a security update that has been “automatically applied” on December 21, 2023, and that no further customer action is required.

It further pointed out that it “deployed a patch to remediate compromised ESG appliances which exhibited indicators of compromise related to the newly identified malware variants” a day later. It did not disclose the scale of the compromise.

That said, the original flaw in the Spreadsheet::ParseExcel Perl module (version 0.65) remains unpatched and has been assigned the CVE identifier CVE-2023-7101, necessitating that downstream users take appropriate remedial action.

According to Mandiant, which has been investigating the campaign, a number of private and public sector organizations located in at least 16 countries are estimated to have been impacted since October 2022.

The latest development once again speaks to UNC4841’s adaptability, leveraging new tactics and techniques to retain access to high priority targets as existing loopholes get closed.