CVE-2016-20048: iSelect Buffer Overflow Vulnerability

CVE-2016-20048 Overview

CVE-2016-20048 is a local buffer overflow vulnerability in iSelect version 1.4.0-2+b1 that enables local attackers to execute arbitrary code. The vulnerability exists in the handling of the -k/--key command-line parameter, which fails to properly validate the size of user-supplied input before copying it to a fixed-size stack buffer.

When an attacker supplies an oversized value to the -k/--key parameter, the application attempts to store the data in a 1024-byte stack buffer without adequate bounds checking. This allows a malicious local user to craft an argument containing a NOP sled, shellcode, and a carefully calculated return address to overflow the buffer and hijack program execution flow.

Critical Impact

Local attackers can achieve arbitrary code execution with the privileges of the user running the iSelect application by exploiting this buffer overflow vulnerability.

Affected Products

• iSelect 1.4.0-2+b1

Discovery Timeline

• 2026-03-28 - CVE-2016-20048 published to NVD
• 2026-03-30 - Last updated in NVD database

Technical Details for CVE-2016-20048

Vulnerability Analysis

This buffer overflow vulnerability stems from improper input validation when processing the -k/--key command-line parameter. The iSelect application allocates a fixed 1024-byte buffer on the stack to store the key parameter value. When a user supplies an argument exceeding this buffer size, the application copies the entire input without verifying its length, resulting in stack memory corruption.

The local attack vector requires an attacker to have access to the target system where iSelect is installed. Once local access is obtained, the attacker can invoke iSelect with a specially crafted oversized argument to the -k parameter. The overflow overwrites adjacent stack memory, including the saved return address, enabling the attacker to redirect execution to attacker-controlled shellcode.

Successful exploitation grants the attacker code execution with the same privilege level as the user running the vulnerable iSelect process. This could allow for further privilege escalation, data exfiltration, or persistence mechanisms depending on the system configuration.

Root Cause

The root cause is a classic stack-based buffer overflow due to insufficient bounds checking on user-controlled input. The application uses an unsafe copy operation that does not validate the length of the -k/--key parameter before storing it in a fixed-size 1024-byte stack buffer. This allows attackers to write beyond the buffer boundaries and corrupt critical stack data including the function return address.

Attack Vector

The attack requires local access to a system with the vulnerable iSelect version installed. An attacker constructs a malicious command-line argument for the -k/--key parameter that exceeds 1024 bytes. The payload typically consists of:

1. Padding/NOP Sled: A sequence of bytes to fill the buffer and reach the return address location
2. Shellcode: Machine code instructions to execute the attacker's desired actions
3. Return Address: An overwritten address pointing back into the NOP sled or directly to the shellcode

When iSelect processes this malicious input, the buffer overflows, the return address is overwritten, and upon function return, execution jumps to the attacker's shellcode. Additional technical details and a proof-of-concept are available through the Exploit-DB #41076 entry.

Detection Methods for CVE-2016-20048

Indicators of Compromise

• Unusual iSelect process execution with extremely long command-line arguments
• System crash logs or core dumps associated with iSelect segmentation faults
• Evidence of shell spawning or unexpected child processes from iSelect
• Anomalous command-line activity involving the -k or --key parameter with lengthy values

Detection Strategies

• Monitor process execution for iSelect invocations with unusually long arguments exceeding typical usage patterns
• Implement application whitelisting to control which users can execute iSelect
• Deploy endpoint detection rules to flag command-line arguments containing potential NOP sled patterns (repeated 0x90 bytes)
• Configure system auditing to log all executions of iSelect with full command-line parameters

Monitoring Recommendations

• Enable command-line logging on systems where iSelect is installed
• Configure SIEM alerts for iSelect process crashes or abnormal terminations
• Monitor for new shell processes spawned as children of iSelect
• Review system integrity monitoring for unexpected file modifications following iSelect execution

How to Mitigate CVE-2016-20048

Immediate Actions Required

• Remove or disable iSelect 1.4.0-2+b1 from systems where it is not strictly required
• Restrict execution permissions for iSelect to only authorized users who require it
• Consider implementing application sandboxing to limit the impact of potential exploitation
• Monitor systems with installed iSelect for signs of exploitation attempts

Patch Information

Users should check for updated versions of iSelect that address this vulnerability. The OSSP Tool Information page provides official information about the iSelect project. The VulnCheck Advisory on iSelect contains additional details about this vulnerability and any available remediation guidance.

If no patched version is available, organizations should evaluate whether iSelect is essential for their operations and consider alternative tools that do not have known vulnerabilities.

Workarounds

• Uninstall iSelect if it is not required for business operations
• Restrict file permissions on the iSelect binary to prevent unauthorized execution
• Use wrapper scripts that validate the length of -k/--key arguments before passing them to iSelect
• Implement operating system-level protections such as ASLR and stack canaries if not already enabled