CVE-2020-15396 in HylaFAX+
Summary
by MITRE
In HylaFAX+ through 7.0.2 and HylaFAX Enterprise, the faxsetup utility calls chown on files in user-owned directories. By winning a race, a local attacker could use this to escalate his privileges to root.
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Analysis
by VulDB Data Team • 07/01/2020
The vulnerability identified as CVE-2020-15396 represents a critical privilege escalation flaw affecting HylaFAX+ versions through 7.0.2 and HylaFAX Enterprise systems. This issue stems from improper privilege management within the faxsetup utility, which is designed to configure fax services on Unix-like systems. The flaw allows local attackers to exploit a race condition during file ownership operations, potentially enabling them to gain root privileges through manipulation of file permissions and ownership.
The technical implementation of this vulnerability involves the faxsetup utility executing chown system calls on files located within user-accessible directories. Under normal circumstances, chown operations require appropriate privileges to change file ownership, but the race condition aspect of this flaw creates a window where an attacker can manipulate file paths or contents between the time when the utility checks file permissions and when it performs the ownership change. This timing discrepancy allows malicious users to substitute files or directories with symbolic links pointing to critical system files, thereby tricking the chown operation into modifying root-owned files or directories.
From an operational perspective, this vulnerability presents a significant risk to organizations relying on HylaFAX services, particularly those running on multi-user systems where local access might be available to unprivileged users. The attack requires local system access and knowledge of the specific race condition timing, but once exploited, the privilege escalation to root level provides complete system control. This includes the ability to modify system files, install malicious software, access sensitive data, and potentially establish persistent backdoors within the affected systems.
The vulnerability aligns with CWE-367, which addresses Time-of-Check to Time-of-Use (TOCTOU) race conditions, and demonstrates how improper resource management can lead to privilege escalation. From an ATT&CK framework perspective, this represents a privilege escalation technique using local system utilities, specifically mapping to T1068 which covers "Local Privilege Escalation" and T1548.1 which covers "Abuse Elevation Control Mechanism." The flaw essentially allows attackers to leverage legitimate system utilities for malicious purposes, bypassing normal access controls through timing-based exploitation.
Mitigation strategies should focus on immediate patching of affected systems to the latest versions of HylaFAX+ that address this race condition. Organizations should also implement strict file system permissions and monitoring to detect unauthorized file modifications. System administrators should review and restrict access to the faxsetup utility, ensuring that only authorized users with appropriate privileges can execute it. Additionally, implementing proper input validation and file path handling within the utility itself would prevent attackers from substituting files during the chown operation. Regular security audits and privilege reviews should be conducted to identify and remediate similar issues in other system utilities that might be vulnerable to similar race condition attacks.