CVE-2021-32555 in Apport
Summary
by MITRE • 06/12/2021
It was discovered that read_file() in apport/hookutils.py would follow symbolic links or open FIFOs. When this function is used by the xorg-hwe-18.04 package apport hooks, it could expose private data to other local users.
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Analysis
by VulDB Data Team • 06/14/2021
The vulnerability identified as CVE-2021-32555 resides within the apport package's hookutils.py module, specifically in the read_file() function implementation. This flaw represents a significant security issue that can be exploited by local attackers to gain unauthorized access to sensitive data. The vulnerability manifests when the read_file() function processes symbolic links or opens named pipes, creating an attack surface that allows malicious users to traverse file system boundaries and access private information that should remain restricted. The issue is particularly concerning because it affects the xorg-hwe-18.04 package's apport hooks, which are designed to collect system information for debugging purposes but inadvertently create opportunities for data leakage.
The technical nature of this vulnerability stems from improper handling of file system objects within the read_file() function, which lacks adequate validation mechanisms to prevent traversal of symbolic links or opening of FIFOs. This behavior directly violates security principles by allowing arbitrary file access patterns that can be manipulated by local users. The function's failure to properly sanitize input paths creates a path traversal vulnerability that aligns with CWE-22 Path Traversal and CWE-352 Cross-Site Request Forgery categories. When apport hooks execute this function, they process system logs and configuration files that may contain sensitive information such as user credentials, system configurations, or private data from other user accounts. The vulnerability operates at the operating system level, leveraging the inherent permissions and access controls that are typically expected to protect system integrity.
The operational impact of this vulnerability extends beyond simple data exposure, as it can enable privilege escalation and information disclosure attacks within local environments. Local users who can manipulate symbolic links or create named pipes can exploit this weakness to read files they normally wouldn't have access to, potentially exposing sensitive system information that could be leveraged for further attacks. This vulnerability particularly affects systems running Ubuntu 18.04 LTS with the xorg-hwe-18.04 package, where apport hooks are actively used for system diagnostics and crash reporting. The implications align with ATT&CK technique T1005 Data from Local System, where adversaries can collect sensitive data through legitimate system processes. Attackers could use this vulnerability to gather system configuration details, user session information, or other sensitive data that may reveal system architecture, user permissions, or application-specific vulnerabilities that could be exploited in subsequent phases of an attack.
Mitigation strategies for CVE-2021-32555 should focus on implementing proper input validation and file system access controls within the apport package. System administrators should ensure that the affected xorg-hwe-18.04 package is updated to a version that addresses this vulnerability through proper handling of symbolic links and FIFOs in the read_file() function. The fix should include implementing checks that prevent following symbolic links or opening named pipes during file reading operations, effectively closing the attack vector. Additionally, system hardening measures should be implemented to restrict file system access patterns and ensure that apport hooks operate within defined security boundaries. Organizations should consider implementing monitoring for suspicious file access patterns and ensure that system updates are applied promptly to address known vulnerabilities. The vulnerability demonstrates the importance of proper file system access controls and input validation in security-critical system components, particularly those involved in system diagnostics and error reporting processes.