Cybersecurity researchers have disclosed details of a critical security flaw in the Roundcube webmail software that has gone unnoticed for a decade and could be exploited to take over susceptible systems and execute arbitrary code.

The vulnerability, tracked as CVE-2025-49113, carries a CVSS score of 9.9 out of 10.0. It has been described as a case of post-authenticated remote code execution via PHP object deserialization.

"Roundcube Webmail before 1.5.10 and 1.6.x before 1.6.11 allows remote code execution by authenticated users because the _from parameter in a URL is not validated in program/actions/settings/upload.php, leading to PHP Object Deserialization," reads the description of the flaw in the NIST's National Vulnerability Database (NVD).

The shortcoming, which affects all versions of the software before and including 1.6.10, has been addressed in 1.6.11 and 1.5.10 LTS. Kirill Firsov, founder and CEO of FearsOff, has been credited with discovering and reporting the flaw.

The Dubai-based cybersecurity company noted in a brief advisory that it intends to make public additional technical details and a proof-of-concept (PoC) "soon" so as to give users sufficient time to apply the necessary patches.

Previously disclosed security vulnerabilities in Roundcube have been a lucrative target for nation-state threat actors like APT28 and Winter Vivern. Last year, Positive Technologies revealed that unidentified hackers attempted to exploit a Roundcube flaw (CVE-2024-37383) as part of a phishing attack designed to steal user credentials.

Then a couple of weeks ago, ESET noted that APT28 had leveraged cross-site scripting (XSS) vulnerabilities in various webmail servers such as Roundcube, Horde, MDaemon, and Zimbra to harvest confidential data from specific email accounts belonging to governmental entities and defense companies in Eastern Europe.