CVE-2020-13753 in WebKitGTK
Summary
by MITRE
The bubblewrap sandbox of WebKitGTK and WPE WebKit, prior to 2.28.3, failed to properly block access to CLONE_NEWUSER and the TIOCSTI ioctl. CLONE_NEWUSER could potentially be used to confuse xdg-desktop-portal, which allows access outside the sandbox. TIOCSTI can be used to directly execute commands outside the sandbox by writing to the controlling terminal's input buffer, similar to CVE-2017-5226.
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Analysis
by VulDB Data Team • 07/08/2025
The vulnerability identified as CVE-2020-13753 affects the bubblewrap sandbox implementation within WebKitGTK and WPE WebKit versions prior to 2.28.3. This represents a critical sandbox escape flaw that undermines the fundamental security boundaries designed to isolate web content from the underlying system. The issue stems from insufficient permission controls within the sandbox mechanism, specifically failing to properly restrict access to two critical system interfaces that can be exploited to bypass sandbox protections.
The technical flaw manifests through two primary attack vectors that work in conjunction to enable unauthorized system access. The first vector involves the improper exposure of CLONE_NEWUSER functionality, which allows processes to create new user namespaces. When combined with xdg-desktop-portal access patterns, this capability can be leveraged to confuse the portal's permission model and gain access to resources outside the intended sandbox boundaries. This vulnerability directly maps to CWE-276, which addresses improper privileges and access control issues in system components.
The second vulnerability involves the unrestricted access to the TIOCSTI ioctl command, a terminal input injection mechanism that was previously exploited in CVE-2017-5226. This ioctl allows direct writing to the controlling terminal's input buffer, enabling attackers to inject commands that execute with the privileges of the sandboxed process. The TIOCSTI vulnerability represents a classic terminal-based attack vector that bypasses traditional sandboxing by operating at the terminal level rather than the process level. This aligns with ATT&CK technique T1059.007 for command and scripting interpreter, specifically targeting terminal input manipulation.
The operational impact of this vulnerability extends beyond simple sandbox bypass to potentially enable full system compromise. Attackers could leverage these combined weaknesses to execute arbitrary commands, access restricted files, or escalate privileges within the sandboxed environment. The vulnerability affects desktop environments that rely on WebKitGTK or WPE WebKit for web rendering, including various Linux desktop applications and web browsers that utilize these components. The exploitation chain requires minimal privileges and can be automated, making it particularly dangerous in environments where users browse untrusted content.
Mitigation strategies should focus on immediate patching of affected WebKitGTK and WPE WebKit installations to version 2.28.3 or later, which implements proper restrictions on both CLONE_NEWUSER and TIOCSTI access. System administrators should also implement additional monitoring for suspicious terminal activity and user namespace creation events. The bubblewrap sandbox configuration should be reviewed to ensure that only necessary capabilities are exposed to sandboxed processes. Organizations should consider implementing additional security controls such as mandatory access controls or extended sandboxing mechanisms that provide stronger isolation boundaries. Network segmentation and application whitelisting can provide additional defense-in-depth layers to limit the potential impact of successful exploitation attempts.