CVE-2020-15397 in HylaFAX+
Summary
by MITRE
HylaFAX+ through 7.0.2 and HylaFAX Enterprise have scripts that execute binaries from directories writable by unprivileged users (e.g., locations under /var/spool/hylafax that are writable by the uucp account). This allows these users to execute code in the context of the user calling these binaries (often root).
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Analysis
by VulDB Data Team • 07/01/2020
The vulnerability identified as CVE-2020-15397 affects HylaFAX+ versions through 7.0.2 and HylaFAX Enterprise installations, presenting a critical privilege escalation risk through insecure script execution patterns. This flaw resides in the fax server's handling of binary execution within directories that are writable by unprivileged users, specifically those under the /var/spool/hylafax directory structure. The security issue stems from the improper handling of PATH environment variables and the execution of system binaries from locations that lack proper access controls. Attackers exploiting this vulnerability can leverage the writable directories to replace legitimate binaries with malicious payloads, effectively gaining elevated privileges during the execution process.
The technical implementation of this vulnerability involves the execution of system binaries through scripts that do not properly validate or sanitize the execution environment. When unprivileged users possess write access to directories containing executables, they can substitute these binaries with malicious versions that will be executed with the privileges of the calling user. In most HylaFAX installations, the uucp account has write permissions to the spool directory, which is commonly used for temporary file storage and execution. This design flaw creates a path for privilege escalation where a low-privilege user can manipulate the execution environment to run arbitrary code with elevated privileges, often root access. The vulnerability is particularly dangerous because it leverages the legitimate execution paths of the fax system rather than requiring direct exploitation of system binaries.
The operational impact of CVE-2020-15397 extends beyond simple privilege escalation, as it can enable attackers to establish persistent access, escalate privileges to full system control, and potentially compromise the entire fax infrastructure. Once an attacker gains root-level access through this vulnerability, they can modify system configurations, install backdoors, exfiltrate sensitive data, or use the compromised system as a launch point for further attacks within the network. The attack surface is significant because many organizations rely on fax systems for critical communications, making these vulnerable installations attractive targets for adversaries seeking persistent access to enterprise environments. The vulnerability affects both standard HylaFAX+ installations and enterprise versions, indicating a widespread issue across different deployment scenarios.
Mitigation strategies for CVE-2020-15397 should focus on implementing proper access controls and privilege separation within the fax system's directory structure. Organizations should immediately restrict write permissions for the uucp account and other unprivileged users to the /var/spool/hylafax directory, ensuring that only authorized system administrators can modify critical components. The most effective remediation involves implementing proper PATH environment variable handling and avoiding the execution of binaries from directories that are writable by unprivileged users. System administrators should also consider implementing file integrity monitoring solutions to detect unauthorized modifications to critical system files. Additionally, upgrading to versions of HylaFAX+ that have addressed this vulnerability is essential, as the fix typically involves stricter access controls and improved binary execution validation. This vulnerability aligns with CWE-732 - Incorrect Permission Assignment for Critical Resource and can be categorized under ATT&CK technique T1068 - Exploitation for Privilege Escalation, emphasizing the critical nature of proper privilege management in system security.