CVE-2024-42010 is a vulnerability identified in the mod_css_styles plugin of Roundcube webmail software versions through 1.5.7 and 1.6.x up to 1.6.7. The root cause is insufficient filtering of CSS token sequences embedded within rendered email messages. Specifically, the plugin fails to adequately sanitize or restrict CSS content, allowing attackers to craft malicious CSS that can be interpreted by the Roundcube client when rendering emails. This flaw enables remote attackers to perform unauthorized information disclosure attacks by embedding CSS that can exfiltrate sensitive data from the victim's mailbox or session context. The vulnerability does not require any privileges or user interaction, making it remotely exploitable over the network simply by sending a malicious email to a target user. The CVSS v3.1 base score is 7.5, reflecting a high severity due to the ease of exploitation (network vector, no privileges, no user interaction) and the impact on confidentiality (high). The vulnerability is classified under CWE-200 (Exposure of Sensitive Information). No patches or exploits in the wild have been reported yet, but the risk remains significant given the widespread use of Roundcube in webmail deployments. The lack of integrity or availability impact means the attack focuses solely on data confidentiality breaches. This vulnerability highlights the risks of insufficient input validation and sanitization in email rendering components, especially those processing CSS content.

The primary impact of CVE-2024-42010 is unauthorized disclosure of sensitive information from users' email accounts accessed via Roundcube webmail. Attackers can remotely exploit this vulnerability by sending specially crafted emails containing malicious CSS, which when rendered by the vulnerable Roundcube instance, leaks confidential data. This can lead to exposure of personal information, internal communications, or credentials stored or accessible through the webmail interface. Since no authentication or user interaction is required, attackers can target any user with an email address on the affected system. Organizations relying on Roundcube for email services risk data breaches that could damage reputation, violate privacy regulations, and lead to further attacks leveraging the disclosed information. The vulnerability does not allow modification or destruction of data, nor does it cause denial of service, but the confidentiality breach alone is significant. The absence of known exploits in the wild currently limits immediate widespread impact, but the potential for targeted attacks against high-value organizations is substantial.

To mitigate CVE-2024-42010, organizations should first verify if their Roundcube installations use versions up to 1.5.7 or 1.6.x through 1.6.7 with the mod_css_styles plugin enabled. Immediate steps include disabling the mod_css_styles plugin if feasible, as this will prevent CSS processing that leads to the vulnerability. If disabling is not possible, organizations should monitor for updates or patches from the Roundcube development team and apply them promptly once available. In the interim, implement email filtering rules to detect and quarantine suspicious emails containing unusual CSS or style elements. Employ Content Security Policy (CSP) headers on the webmail server to restrict CSS execution contexts and reduce the risk of CSS-based attacks. Additionally, educate users about the risks of opening emails from unknown or untrusted sources. Network-level protections such as intrusion detection systems (IDS) can be tuned to detect anomalous email content patterns. Finally, conduct regular security assessments of webmail infrastructure to identify and remediate similar input validation weaknesses.