CVE-2019-7742 in Joomla
Summary
by MITRE
An issue was discovered in Joomla! before 3.9.3. A combination of specific web server configurations, in connection with specific file types and browser-side MIME-type sniffing, causes an XSS attack vector.
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Analysis
by VulDB Data Team • 07/10/2023
The vulnerability identified as CVE-2019-7742 represents a sophisticated cross-site scripting flaw within the Joomla! content management system that emerged prior to version 3.9.3. This security weakness exploits a complex interaction between web server configurations, file type handling, and browser-based MIME-type detection mechanisms to create a persistent attack vector. The flaw demonstrates how seemingly innocuous configuration elements can combine to create significant security risks when operating in specific environmental conditions.
The technical root cause of this vulnerability stems from the improper handling of file content and MIME-type detection in Joomla!'s file upload and processing mechanisms. When specific web server configurations are combined with particular file types and browser-side MIME-type sniffing behaviors, the system fails to properly validate or sanitize content that should be restricted. This creates an environment where malicious actors can craft payloads that bypass normal security controls, particularly when browsers attempt to determine file types through content inspection rather than relying solely on server-provided headers.
The operational impact of CVE-2019-7742 extends beyond typical XSS vulnerabilities due to its reliance on environmental configurations rather than direct application flaws. Attackers can leverage this vulnerability to execute malicious scripts in the context of a victim's browser session, potentially leading to session hijacking, data theft, or privilege escalation. The vulnerability's reliance on specific server configurations means that not all Joomla! installations are equally affected, but those with the problematic combination of settings create an exploitable condition that could be leveraged by threat actors.
Security professionals should note that this vulnerability aligns with CWE-79 which categorizes cross-site scripting flaws, and demonstrates characteristics consistent with ATT&CK technique T1203 - Exploitation for Client Execution. The vulnerability requires specific preconditions to be exploited effectively, making it a targeted threat rather than a widespread vulnerability. Organizations should prioritize updating to Joomla! version 3.9.3 or later, while also reviewing their web server configurations to ensure they do not inadvertently create conditions that could enable this attack vector. Additionally, implementing proper content security policies and validating all file uploads through multiple verification mechanisms will help mitigate the risk associated with this specific vulnerability pattern.