CVE-2021-32547 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 openjdk-lts 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-2021-32547 resides within the apport package's hookutils.py module, specifically in the read_file() function implementation. This flaw represents a critical security issue that emerges from improper handling of symbolic links and named pipes during file operations. The vulnerability affects systems utilizing the openjdk-lts package which employs apport hooks for crash reporting and system diagnostics. When the read_file() function processes files that are symbolic links or FIFOs, it fails to properly validate or restrict access to these special file types, creating an exploitable condition that can lead to unauthorized data exposure.
The technical implementation flaw stems from the function's lack of proper file type validation and access control mechanisms. When symbolic links are encountered, the function follows them without verifying whether the target file should be accessible to the current user context. Similarly, when FIFOs are processed, the function opens these named pipes without adequate safeguards against maliciously crafted symbolic link chains or unauthorized access patterns. This behavior directly violates security principles of least privilege and proper file access controls. The vulnerability manifests when the openjdk-lts package's apport hooks invoke read_file() to process crash dump files or system logs, potentially exposing sensitive information such as private keys, passwords, or other confidential data stored in files accessible through symbolic link traversal.
The operational impact of this vulnerability extends beyond simple data exposure to encompass potential privilege escalation and information disclosure attacks. Local users can exploit this condition to gain access to files that should normally be restricted, particularly when these files are located in directories accessible through symbolic link traversal paths. The vulnerability affects systems running Ubuntu and other Debian-based distributions that utilize the apport crash reporting framework alongside openjdk-lts packages. Attackers could leverage this flaw to extract sensitive information from system logs, configuration files, or other data that should remain private, potentially leading to further compromise of the affected systems.
Security mitigations for CVE-2021-32547 should focus on implementing proper file validation and access control within the apport hookutils.py module. The recommended approach involves modifying the read_file() function to explicitly check file types and reject symbolic links or FIFOs during processing. This aligns with CWE-22 principle of preventing path traversal attacks and CWE-276 principle of using proper access controls. System administrators should ensure that affected systems receive updates from their respective distribution vendors, as Ubuntu has released patches addressing this specific vulnerability. Additionally, implementing proper file system permissions and monitoring for unauthorized symbolic link creation can provide defense-in-depth measures. The ATT&CK framework categorizes this vulnerability under T1083 (File and Directory Discovery) and T1005 (Data from Local System) techniques, as attackers could use this flaw to discover and extract sensitive data from local system resources. Organizations should also consider implementing automated security scanning to identify systems running vulnerable versions of apport and openjdk-lts packages, ensuring comprehensive coverage of their infrastructure against this and similar path traversal vulnerabilities.