CVE-2019-3690 in chkstat Tool
Summary
by MITRE
The chkstat tool in the permissions package followed symlinks before commit a9e1d26cd49ef9ee0c2060c859321128a6dd4230 (please also check the additional hardenings after this fix). This allowed local attackers with control over a path that is traversed by chkstat to escalate privileges.
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Analysis
by VulDB Data Team • 03/07/2024
The vulnerability identified as CVE-2019-3690 resides within the chkstat tool of the permissions package, a critical component in Unix-like operating systems responsible for managing file permissions and ownership. This flaw represents a classic privilege escalation vulnerability that exploits improper symlink handling during file traversal operations. The chkstat utility, designed to verify and correct file permissions across system directories, exhibits a dangerous behavior where it follows symbolic links without sufficient validation, creating a pathway for malicious actors to manipulate the tool's execution flow.
The technical root cause of this vulnerability stems from the tool's failure to properly handle symbolic links during directory traversal operations. When chkstat processes a directory structure containing symbolic links, it follows these links before performing necessary security checks, allowing attackers to craft malicious symlink chains that can redirect the tool's operations to arbitrary files. This behavior creates a race condition scenario where an attacker can manipulate the filesystem between the time chkstat checks a path and when it actually operates on the target file. The vulnerability specifically manifests when the tool processes paths that contain symlinks, enabling attackers to place malicious symlinks in locations that chkstat will traverse, potentially allowing privilege escalation.
The operational impact of this vulnerability extends beyond simple local privilege escalation, as it can be exploited by unprivileged users to gain elevated system privileges. Attackers can leverage this weakness to modify critical system files, inject malicious code into system binaries, or manipulate permission settings to maintain persistent access. The vulnerability's exploitation requires local access and control over specific paths that chkstat will traverse, but the consequences are severe enough to warrant immediate attention. This flaw essentially allows attackers to bypass standard security controls that rely on chkstat's proper operation, making it particularly dangerous in environments where system integrity checks are critical.
The security implications of CVE-2019-3690 align with CWE-59, which addresses improper handling of symbolic links, and relates to ATT&CK technique T1068, which covers privilege escalation through local exploits. This vulnerability demonstrates how seemingly benign system utilities can become attack vectors when proper security considerations are not applied to file traversal operations. The fix implemented after the vulnerability disclosure involved modifying the chkstat tool to avoid following symbolic links during path resolution, implementing a more secure approach that prevents attackers from manipulating the tool's behavior through symlink manipulation. Organizations should ensure that all systems running affected versions of the permissions package have been patched and that proper system integrity verification mechanisms are in place to detect any potential exploitation attempts.
This vulnerability serves as a reminder of the critical importance of secure coding practices in system utilities, particularly those involved in permission management and system integrity checks. The flaw highlights the need for careful consideration of symbolic link handling in all file traversal operations, as well as the importance of validating file paths before performing operations that could affect system security. The remediation process should include comprehensive system auditing to identify any potential exploitation attempts and implementation of monitoring solutions to detect unusual chkstat operations that might indicate attempted exploitation.