CVE-2013-5680 in HylaFAX+
Summary
by MITRE
Heap-based buffer overflow in hfaxd in HylaFAX+ 5.2.4 through 5.5.3, when using LDAP authentication, might allow remote attackers to cause a denial of service (child hang) or execute arbitrary code via a long USER command.
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Analysis
by VulDB Data Team • 05/09/2026
The vulnerability identified as CVE-2013-5680 represents a critical heap-based buffer overflow in the hfaxd component of HylaFAX+ versions 5.2.4 through 5.5.3 when LDAP authentication is enabled. This flaw exists within the fax server's authentication handling mechanism and specifically targets the USER command processing functionality. The vulnerability stems from inadequate input validation and bounds checking within the heap memory allocation routines that process LDAP authentication requests. When a remote attacker submits a malformed USER command containing excessive data, the application fails to properly validate the input length before copying it into a fixed-size buffer allocated on the heap. This condition creates a classic buffer overflow scenario where adjacent heap memory regions become overwritten, potentially leading to unpredictable application behavior. The vulnerability operates under CWE-121, which classifies heap-based buffer overflows as a fundamental memory safety issue, and aligns with ATT&CK technique T1203, which covers the exploitation of input validation flaws for code execution. The impact extends beyond simple denial of service to include potential arbitrary code execution, making this a severe security concern for any organization relying on HylaFAX+ for fax services. The specific context of LDAP authentication amplifies the risk because it provides an additional attack vector through which malicious actors can exploit the vulnerable code path, particularly in environments where LDAP is used for centralized user management.
The technical implementation of this vulnerability involves the hfaxd daemon's handling of user authentication requests through the LDAP protocol. When processing a USER command, the system allocates memory on the heap to store the authentication credentials provided by the client. However, the code fails to validate whether the incoming USER command exceeds the allocated buffer size, allowing an attacker to overflow the heap buffer and overwrite adjacent memory structures. This overflow can corrupt heap metadata, function pointers, or return addresses, potentially leading to execution of arbitrary code or causing the daemon to hang indefinitely. The heap-based nature of the vulnerability means that the attack can be particularly insidious because heap corruption can manifest in unpredictable ways, making exploitation more challenging but also more dangerous. The specific conditions that trigger this vulnerability require the system to be configured with LDAP authentication enabled, which is common in enterprise environments where centralized authentication is preferred. The vulnerability demonstrates poor input sanitization practices and highlights the importance of implementing robust bounds checking mechanisms in network services that handle user-provided data, particularly those operating in privileged contexts.
The operational impact of CVE-2013-5680 extends from immediate service disruption to potential system compromise within affected environments. A successful exploitation can result in a denial of service condition where the fax daemon becomes unresponsive, effectively blocking all fax operations and potentially causing business continuity issues for organizations relying on fax communications. More critically, the vulnerability's potential for arbitrary code execution means that attackers could gain control over the fax server, potentially leading to complete system compromise, data exfiltration, or use of the compromised system as a launching point for further attacks within the network. The vulnerability affects organizations using HylaFAX+ in enterprise fax environments, particularly those with LDAP integration, making it relevant to IT infrastructure managers, security administrators, and network operations teams. The risk is compounded by the fact that fax servers often operate with elevated privileges and may have access to sensitive organizational data, including patient records in healthcare environments or financial information in banking sectors. Organizations may also face regulatory compliance issues if the vulnerability leads to unauthorized access to protected data, as it could violate standards such as HIPAA, PCI DSS, or SOX requirements that mandate robust security controls for sensitive information handling.
Mitigation strategies for CVE-2013-5680 should prioritize immediate patching of affected systems, as the vulnerability affects multiple versions of HylaFAX+ and has been identified as a critical security risk by security vendors and organizations. Organizations should implement network segmentation to limit access to fax servers and restrict the USER command to trusted administrative networks only. Additionally, monitoring and logging of fax server activities should be enhanced to detect potential exploitation attempts, particularly unusual USER command patterns or extended input lengths. The implementation of input validation controls and bounds checking should be enforced at multiple layers including application-level defenses, network firewalls, and intrusion detection systems. Security teams should also consider implementing application whitelisting policies that restrict execution of unauthorized code on fax servers. Organizations should conduct thorough vulnerability assessments to identify all systems running affected HylaFAX+ versions and ensure that LDAP authentication configurations are properly reviewed and secured. The vulnerability highlights the importance of regular security updates and patch management processes, as well as the need for comprehensive security testing of network services, particularly those handling external authentication requests. Organizations should also consider implementing security awareness training for system administrators to recognize and respond to potential exploitation attempts, as the vulnerability's exploitation often begins with reconnaissance and initial access through LDAP authentication mechanisms that are commonly targeted by attackers.