CVE-2008-5396 in Zaptel
Summary
by MITRE
Array index error in the (1) torisa.c and (2) dahdi/tor2.c drivers in Zaptel (aka DAHDI) 1.4.11 and earlier allows local users in the dialout group to overwrite an integer value in kernel memory by writing to /dev/zap/ctl, related to missing validation of the sync field associated with the ZT_SPANCONFIG ioctl.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 04/07/2025
The vulnerability identified as CVE-2008-5396 represents a critical array index error within the Zaptel kernel drivers that affects systems utilizing DAHDI (Digium Asterisk Hardware Driver Interface) version 1.4.11 and earlier. This flaw exists in two primary driver components torisa.c and dahdi/tor2.c which handle telephony signaling and hardware communication for various telephony devices including PRI (Primary Rate Interface) and BRI (Basic Rate Interface) protocols. The vulnerability specifically targets the ZT_SPANCONFIG ioctl command which is used to configure telephony spans within the DAHDI framework, making it a core component of telephony system administration and operation.
The technical flaw stems from insufficient validation of the sync field parameter within the ZT_SPANCONFIG ioctl implementation. When a local user with dialout group membership writes to the /dev/zap/ctl device file, the system fails to properly validate the sync field value before using it as an array index. This missing input validation creates a classic buffer overflow condition where an attacker can manipulate kernel memory by providing an out-of-bounds index value. The vulnerability is particularly dangerous because it allows local privilege escalation to kernel mode, enabling arbitrary memory modification that can lead to system compromise, denial of service, or data corruption.
The operational impact of this vulnerability is significant for telephony systems running affected DAHDI versions, particularly in enterprise environments where telephony infrastructure is critical. Attackers with dialout group membership can exploit this flaw to overwrite kernel memory locations, potentially leading to privilege escalation, system instability, or complete system compromise. The vulnerability is classified under CWE-129 as an "Improper Validation of Array Index" and aligns with ATT&CK technique T1068 which covers "Exploitation for Privilege Escalation." The local nature of the attack means that any user with dialout group access can potentially exploit this vulnerability, making it particularly concerning in multi-user environments where such group membership might be granted for legitimate telephony operations.
Mitigation strategies for CVE-2008-5396 should focus on immediate patching of the DAHDI framework to version 1.4.12 or later where the missing validation has been implemented. System administrators should also consider restricting access to the /dev/zap/ctl device file and the dialout group membership to minimize the attack surface. Additional security measures include implementing proper input validation at the kernel level, monitoring for suspicious ioctl calls, and ensuring that only authorized users have dialout group membership. The vulnerability demonstrates the critical importance of input validation in kernel space operations and serves as a reminder of the potential for local privilege escalation through seemingly benign device driver interfaces. Organizations should conduct thorough security assessments of their telephony infrastructure and ensure all kernel drivers are kept up to date with the latest security patches to prevent exploitation of similar vulnerabilities.