The U.S. Cybersecurity and Infrastructure Security Agency (CISA) has identified a medium-severity security flaw in Roundcube email software, denoted as CVE-2023-43770, and included it in its Known Exploited Vulnerabilities catalog. This vulnerability is related to a cross-site scripting (XSS) issue arising from the handling of linkrefs in plain text messages. CISA’s alert highlights the risk of information disclosure due to malicious link references, emphasizing the importance of addressing this vulnerability promptly.
The flaw affects Roundcube versions before 1.4.14, 1.5.x before 1.5.4, and 1.6.x before 1.6.3, according to the description provided by the National Vulnerability Database (NVD). To mitigate the risk, Roundcube maintainers released version 1.6.3 on September 15, 2023, providing a fix for the XSS vulnerability. The discovery of this vulnerability is credited to Niraj Shivtarkar, a security researcher at Zscaler, underscoring the collaborative efforts in identifying and addressing security issues in software systems.
Although the specifics of how the vulnerability is exploited in the wild are not yet known, previous incidents involving web-based email clients suggest potential risks. Threat actors, including Russia-linked groups like APT28 and Winter Vivern, have previously weaponized vulnerabilities in similar platforms. As a precautionary measure, U.S. Federal Civilian Executive Branch (FCEB) agencies have been directed to implement the vendor-provided fixes by March 4, 2024, to safeguard their networks against potential threats posed by this vulnerability.