CVE-2011-1492 in Roundcube
Summary
by MITRE
steps/utils/modcss.inc in Roundcube Webmail before 0.5.1 does not properly verify that a request is an expected request for an external Cascading Style Sheets (CSS) stylesheet, which allows remote authenticated users to trigger arbitrary outbound TCP connections from the server, and possibly obtain sensitive information, via a crafted request.
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Analysis
by VulDB Data Team • 10/21/2021
The vulnerability identified as CVE-2011-1492 resides within the Roundcube Webmail application's handling of CSS stylesheet requests, specifically in the steps/utils/modcss.inc file. This flaw represents a classic case of improper input validation and trust verification in web applications. The vulnerability affects versions of Roundcube prior to 0.5.1, indicating it was present in a widely used webmail platform that many organizations relied upon for email services. The security issue stems from the application's failure to properly authenticate and validate CSS stylesheet requests, creating a pathway for malicious actors to exploit the system's outbound connection capabilities.
The technical mechanism of this vulnerability involves the application's insufficient verification of external CSS requests, allowing authenticated users to manipulate the system into making arbitrary outbound TCP connections. This occurs because the modcss.inc component does not adequately validate the source or legitimacy of CSS requests, enabling attackers to craft specific requests that bypass normal security checks. The flaw essentially allows an attacker to influence the application's network behavior by manipulating CSS loading mechanisms, which can result in unintended outbound communications from the server. This type of vulnerability falls under CWE-20, which addresses improper input validation, and can be classified as a form of insecure direct object reference when the system fails to verify the legitimacy of external resource requests.
The operational impact of this vulnerability extends beyond simple network connectivity issues, as it can potentially enable information disclosure and reconnaissance activities. When an authenticated user triggers this vulnerability, the server may establish outbound connections to arbitrary external hosts, potentially allowing attackers to exfiltrate data or establish command and control channels. This creates a significant risk for organizations as it allows for covert communication channels and can be exploited to gather sensitive information from the internal network. The vulnerability essentially transforms the webmail server into a potential proxy for malicious network activities, which can be particularly dangerous in enterprise environments where such servers are often centrally managed and have access to sensitive organizational data.
The exploitation of this vulnerability aligns with several techniques documented in the MITRE ATT&CK framework, particularly those related to command and control communications and exfiltration. Attackers could leverage this flaw to establish covert channels, perform network reconnaissance, or even use the compromised server as a stepping stone for further attacks within the network infrastructure. The authentication requirement for exploitation means that attackers would need valid credentials, but this still represents a significant risk as it can be combined with other vulnerabilities or social engineering techniques to gain access. Organizations should consider implementing network monitoring and anomaly detection to identify unusual outbound connections that may indicate exploitation of this vulnerability.
Mitigation strategies for CVE-2011-1492 primarily involve upgrading to Roundcube Webmail version 0.5.1 or later, which contains the necessary fixes for proper CSS request validation. Additionally, organizations should implement network segmentation and firewall rules to restrict outbound connections from webmail servers, particularly to untrusted external domains. Input validation should be strengthened at multiple levels, including implementing strict validation of CSS request parameters and ensuring that all external resource loading is properly authenticated and authorized. Security monitoring should include detection of unusual outbound TCP connections from webmail servers, as this behavior would be indicative of exploitation attempts. Organizations should also consider implementing web application firewalls and content filtering solutions to provide additional layers of protection against similar vulnerabilities in the future.