CVE-2006-3126 in capi4hylafax
Summary
by MITRE
c2faxrecv in capi4hylafax 01.02.03 allows remote attackers to execute arbitrary commands via null (\0) and shell metacharacters in the TSI string, as demonstrated by a fax from an anonymous number.
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Analysis
by VulDB Data Team • 07/10/2019
The vulnerability identified as CVE-2006-3126 resides within the c2faxrecv component of capi4hylafax version 01.02.03, representing a critical remote command execution flaw that enables attackers to gain unauthorized system access. This vulnerability specifically targets the TSI string processing mechanism, which is responsible for handling the Transmitting Station Identifier information in fax communications. The flaw manifests when the system fails to properly sanitize input data, particularly when processing fax transmissions from anonymous numbers, creating an exploitable condition that can be leveraged by remote threat actors.
The technical implementation of this vulnerability stems from inadequate input validation and sanitization within the fax receiving subsystem. When a fax is received with a TSI string containing null characters or shell metacharacters, the system processes these inputs without proper escaping or filtering mechanisms. This insufficient sanitization allows attackers to inject malicious commands that get executed within the context of the fax receiving process. The vulnerability specifically exploits the command execution flow where fax data is parsed and subsequently used to construct system commands, creating a classic command injection scenario that can be weaponized across network boundaries.
From an operational impact perspective, this vulnerability presents a significant threat to organizations relying on fax-based communication systems for business operations. Attackers can leverage this flaw to execute arbitrary code on affected systems, potentially gaining full control over fax servers and associated network resources. The remote nature of the exploit means that threat actors do not require physical access or local network presence to exploit the vulnerability, making it particularly dangerous in environments where fax servers are accessible from external networks. The impact extends beyond simple command execution to potential privilege escalation, data exfiltration, and lateral movement within compromised networks.
The exploitation of this vulnerability aligns with several ATT&CK framework techniques including T1059.001 for command and script interpreter, and T1078 for valid accounts, as attackers can leverage the system's legitimate fax processing capabilities to execute malicious commands. This vulnerability also maps to CWE-78, which describes improper neutralization of special elements used in OS commands, and CWE-20, which covers input validation issues in software. Organizations should implement immediate mitigations including input validation patches, network segmentation to limit fax server exposure, and regular security updates to prevent exploitation. The recommended remediation involves upgrading to patched versions of capi4hylafax, implementing proper input sanitization measures, and establishing network monitoring to detect anomalous fax traffic patterns that may indicate exploitation attempts.