CVE-2011-4212 in App Engine Python SDK
Summary
by MITRE
The sandbox environment in the Google App Engine Python SDK before 1.5.4 does not properly prevent os.popen calls, which allows local users to bypass intended access restrictions and execute arbitrary commands via a dev_appserver.RestrictedPathFunction._original_os reference within the code parameter to _ah/admin/interactive/execute, a different vulnerability than CVE-2011-1364.
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Analysis
by VulDB Data Team • 01/25/2018
The vulnerability identified as CVE-2011-4212 represents a critical security flaw in the Google App Engine Python SDK sandbox environment that existed prior to version 1.5.4. This issue specifically targets the sandbox's ability to restrict system-level operations, creating a pathway for local attackers to execute arbitrary commands on the underlying system. The vulnerability exploits a design weakness in the sandbox's implementation of the os.popen function, which should have been restricted to prevent unauthorized system interactions. The flaw manifests through the dev_appserver.py component that handles administrative functions, particularly within the _ah/admin/interactive/execute endpoint where the RestrictedPathFunction._original_os reference is improperly handled.
The technical implementation of this vulnerability stems from insufficient sandbox isolation mechanisms within the Google App Engine SDK development environment. When users interact with the interactive admin console through the _ah/admin/interactive/execute endpoint, the system fails to properly validate or restrict the os.popen function calls that are passed through the code parameter. This allows malicious code to reference the original os module functionality through the _original_os attribute, effectively bypassing the sandbox's intended restrictions. The vulnerability operates under the principle that the sandbox should prevent access to system-level functions while still allowing legitimate application code to execute within controlled parameters. However, the flawed implementation allows attackers to leverage the internal reference mechanism to gain access to unrestricted system commands.
The operational impact of CVE-2011-4212 extends beyond simple privilege escalation, as it provides attackers with complete control over the development environment's underlying operating system. Local users who can access the development server can execute arbitrary commands with the privileges of the user running the dev_appserver process, potentially leading to complete system compromise. This vulnerability is particularly concerning in development environments where multiple developers may have access to the same system, as it allows unauthorized individuals to escalate privileges and execute malicious code. The attack vector specifically targets the administrative interface of the development server, making it accessible to anyone with knowledge of the internal API endpoints. This issue falls under the CWE-250 category for "Execute Program with Unnecessary Privileges" and aligns with ATT&CK techniques involving privilege escalation and command execution.
The mitigation for CVE-2011-4212 requires immediate upgrade to Google App Engine Python SDK version 1.5.4 or later, which includes proper sandbox restrictions for os.popen calls and enhanced validation of administrative function parameters. Organizations should also implement network segmentation to limit access to development servers and ensure that only authorized personnel can interact with the administrative interfaces. Additionally, system administrators should monitor for any suspicious activity in the development environment and consider implementing additional logging and monitoring solutions to detect unauthorized command execution attempts. The fix addresses the core issue by properly sanitizing the code parameter and preventing the bypass of sandbox restrictions through internal reference mechanisms, ensuring that the os.popen function calls are properly isolated from the underlying system access. This vulnerability demonstrates the critical importance of proper sandbox implementation in development environments and the potential consequences of inadequate privilege separation in application frameworks.