CVE-2020-27348 in snapcraft
Summary
by MITRE • 12/04/2020
In some conditions, a snap package built by snapcraft includes the current directory in LD_LIBRARY_PATH, allowing a malicious snap to gain code execution within the context of another snap if both plug the home interface or similar. This issue affects snapcraft versions prior to 4.4.4, prior to 2.43.1+16.04.1, and prior to 2.43.1+18.04.1.
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Analysis
by VulDB Data Team • 12/12/2020
This vulnerability represents a critical privilege escalation flaw in the snap package management system that exploits insecure environment variable handling during package construction. The issue stems from snapcraft's improper configuration of the LD_LIBRARY_PATH environment variable when building snap packages, specifically including the current working directory in the library search path. This creates a dangerous condition where maliciously crafted snap packages can manipulate the dynamic linking process of other snaps that share the same home interface plug. The vulnerability is particularly concerning because it leverages the trusted relationship between snaps that share the home interface, allowing a compromised snap to execute arbitrary code within the context of another snap with elevated privileges. The flaw exists in multiple versions of snapcraft across different ubuntu releases, with specific affected versions including those prior to 4.4.4, 2.43.1+16.04.1, and 2.43.1+18.04.1, indicating a widespread impact across the snap ecosystem.
The technical implementation of this vulnerability involves the manipulation of dynamic library loading mechanisms through improper environment variable configuration. When snapcraft builds packages, it inadvertently sets LD_LIBRARY_PATH to include the current directory, which means that any library files present in the build directory can be loaded by the snap runtime. An attacker with access to create or modify a snap package can place malicious shared libraries in the current directory during the build process, and these libraries will be loaded when the snap executes, particularly when other snaps with the home interface plug are running. This creates a privilege escalation vector where a malicious snap can execute code with the same privileges as another snap, effectively bypassing the isolation mechanisms that snap is designed to provide. The vulnerability is classified under CWE-427 Uncontrolled Search Path Element, which specifically addresses the issue of insecure library loading due to uncontrolled search paths in the environment.
The operational impact of this vulnerability extends beyond simple code execution to represent a fundamental breakdown in the security model of the snap package system. When both snaps plug the home interface, they share access to the same user directory space, creating a trusted execution environment where the malicious snap can manipulate the runtime environment of other snaps. This allows for various attack vectors including privilege escalation, data theft, and persistent access within the user's environment. The vulnerability essentially undermines the principle of least privilege that snap packages are designed to enforce, enabling a single compromised snap to potentially compromise the entire user session. Attackers can exploit this by creating malicious snaps that contain shared libraries designed to execute arbitrary code when loaded by other snaps, effectively creating a form of cross-snap privilege escalation that bypasses normal security boundaries. The impact is particularly severe in environments where users run multiple snaps that share the home interface, as this vulnerability can be exploited without requiring additional user interaction or elevated privileges.
Mitigation strategies for this vulnerability focus on updating snapcraft to versions that properly handle the LD_LIBRARY_PATH environment variable and prevent the inclusion of the current directory in library search paths. System administrators should immediately upgrade to snapcraft versions 4.4.4 or later, or the appropriate version for their ubuntu release, to eliminate the risk of exploitation. Additionally, users should avoid running snaps that have not been verified as legitimate, particularly in environments where multiple snaps share the home interface. The security community recommends implementing strict access controls and monitoring for suspicious library loading patterns, as well as regularly auditing snap packages for potential malicious content. Organizations should also consider implementing network segmentation and monitoring solutions that can detect unusual library loading behavior that might indicate exploitation attempts. This vulnerability highlights the importance of proper environment variable handling in build systems and serves as a reminder that insecure build processes can create persistent security flaws in the runtime environment. The ATT&CK framework would categorize this under privilege escalation techniques, specifically using environment variables to manipulate program execution flow, and potentially under persistence mechanisms if exploited for long-term access within the user environment.