CVE-2019-7307 in Apport
Summary
by MITRE
Apport before versions 2.14.1-0ubuntu3.29+esm1, 2.20.1-0ubuntu2.19, 2.20.9-0ubuntu7.7, 2.20.10-0ubuntu27.1, 2.20.11-0ubuntu5 contained a TOCTTOU vulnerability when reading the users ~/.apport-ignore.xml file, which allows a local attacker to replace this file with a symlink to any other file on the system and so cause Apport to include the contents of this other file in the resulting crash report. The crash report could then be read by that user either by causing it to be uploaded and reported to Launchpad, or by leveraging some other vulnerability to read the resulting crash report, and so allow the user to read arbitrary files on the system.
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Analysis
by VulDB Data Team • 06/18/2024
The vulnerability identified as CVE-2019-7307 represents a time-of-check to time-of-use weakness in the Apport crash reporting system used by Ubuntu and other Debian-based distributions. This flaw exists in versions of Apport prior to 2.14.1-0ubuntu3.29+esm1, 2.20.1-0ubuntu2.19, 2.20.9-0ubuntu7.7, 2.20.10-0ubuntu27.1, and 2.20.11-0ubuntu5, creating a significant security risk through a classic race condition exploit. The vulnerability specifically affects how Apport handles the user's ~/.apport-ignore.xml configuration file during crash report generation processes.
The technical implementation of this vulnerability stems from Apport's improper handling of file operations when processing user configuration files. During the crash reporting process, Apport performs a check to determine if certain files should be ignored, but this check occurs at a different point in time than when the actual file content is read. This temporal discrepancy allows a malicious user to manipulate the file system between the check and read operations. The flaw manifests when an attacker creates a symbolic link pointing to a sensitive file such as /etc/shadow or /etc/passwd, and places this symlink where Apport expects to find the legitimate ~/.apport-ignore.xml file. When Apport processes the crash report, it follows the symlink and includes the contents of the target file in the crash report output.
This vulnerability operates under the Common Weakness Enumeration category CWE-367, which specifically addresses Time-of-Check to Time-of-Use race conditions. The operational impact of this flaw extends beyond simple information disclosure, as it provides a mechanism for privilege escalation and lateral movement within a system. A local attacker with minimal privileges can leverage this vulnerability to access files that would normally be restricted to specific user groups or system administrators. The attack vector requires the attacker to have write access to their own home directory, which is typically available to all users on a system. Once exploited, the vulnerability allows access to arbitrary files on the system through the crash report mechanism, potentially exposing sensitive system information including password hashes, configuration files, and other critical data.
The exploitation chain begins with the attacker creating a malicious symbolic link in their home directory, followed by triggering a crash or system event that causes Apport to generate a crash report. The resulting crash report contains the contents of the targeted file, which can then be accessed by the user either through the normal upload process to Launchpad or by leveraging additional vulnerabilities to read the crash report directly from the local filesystem. This vulnerability aligns with ATT&CK technique T1083 (File and Directory Discovery) and T1005 (Data from Local System) as it enables unauthorized file access through legitimate system processes. The remediation involves updating Apport to versions that properly implement atomic file operations or use file descriptor-based access patterns that eliminate the race condition. System administrators should prioritize patching affected systems and implementing monitoring for suspicious symbolic link creation in user directories. The vulnerability demonstrates the importance of proper file access controls and the need for atomic operations in security-sensitive applications to prevent attackers from exploiting temporal inconsistencies in file handling processes.