CVE-2016-20040: TiEmu Buffer Overflow Vulnerability

CVE-2016-20040 Overview

CVE-2016-20040 is a buffer overflow vulnerability affecting TiEmu 3.03-nogdb+dfsg-3, a popular Texas Instruments calculator emulator. The vulnerability exists in the ROM parameter handling component and allows local attackers to crash the application or potentially execute arbitrary code. By supplying an oversized ROM parameter to the tiemu command-line interface, attackers can overflow a stack buffer and overwrite the instruction pointer with malicious addresses, gaining control of program execution flow.

Critical Impact

Local attackers can exploit this buffer overflow to crash TiEmu or achieve arbitrary code execution by manipulating the ROM parameter to overwrite critical memory addresses.

Affected Products

• TiEmu 3.03-nogdb+dfsg-3

Discovery Timeline

• 2026-03-28 - CVE CVE-2016-20040 published to NVD
• 2026-03-30 - Last updated in NVD database

Technical Details for CVE-2016-20040

Vulnerability Analysis

This vulnerability stems from improper bounds checking when handling the ROM parameter in TiEmu's command-line interface. When processing user-supplied ROM file paths or identifiers, the application copies the input into a fixed-size stack buffer without validating the input length against the buffer's capacity. This classic stack-based buffer overflow allows an attacker to write beyond the allocated buffer space.

The vulnerability is exploitable locally, requiring no privileges and no user interaction. A successful exploit grants the attacker the ability to overwrite the return address on the stack, redirecting execution to attacker-controlled code. This can result in complete compromise of confidentiality, integrity, and availability within the context of the running TiEmu process.

Root Cause

The root cause is insufficient input validation in the ROM parameter handling code. The application fails to verify that user-supplied input does not exceed the size of the destination stack buffer before performing the copy operation. This allows attackers to craft inputs specifically designed to overflow the buffer and control the instruction pointer.

Attack Vector

The attack is performed locally through the TiEmu command-line interface. An attacker crafts an oversized ROM parameter value that exceeds the expected buffer size. When TiEmu attempts to process this malformed input, the overflow occurs, corrupting adjacent stack memory including the saved return address. The attacker can calculate precise offsets to overwrite the instruction pointer with addresses pointing to shellcode or ROP gadgets.

The vulnerability is documented on Exploit-DB #39692, which provides technical details about the exploitation methodology. Additional information is available from the VulnCheck Advisory for TiEmu.

Detection Methods for CVE-2016-20040

Indicators of Compromise

• Unexpected crashes or segmentation faults in TiEmu processes
• Anomalous command-line arguments containing excessively long ROM parameter values
• Process memory dumps showing corrupted stack frames or unusual return addresses
• Suspicious child processes spawned from TiEmu execution context

Detection Strategies

• Monitor for TiEmu process crashes with buffer overflow-related error signatures
• Implement application whitelisting to detect unauthorized code execution from TiEmu's process space
• Configure endpoint detection to alert on command-line arguments exceeding normal length thresholds for TiEmu
• Review system logs for repeated TiEmu execution attempts with varying parameter lengths (potential exploitation attempts)

Monitoring Recommendations

• Enable crash dump collection for TiEmu to facilitate forensic analysis of exploitation attempts
• Configure process monitoring to detect abnormal behavior patterns in TiEmu execution
• Implement file integrity monitoring on systems where TiEmu is installed
• Establish baseline behavior for TiEmu usage to identify anomalies

How to Mitigate CVE-2016-20040

Immediate Actions Required

• Consider removing or restricting access to TiEmu 3.03-nogdb+dfsg-3 until a patched version is available
• Limit TiEmu execution to trusted users and controlled environments only
• Implement application control policies to restrict TiEmu usage where not required
• Monitor for and block exploitation attempts using endpoint security solutions

Patch Information

No official vendor patch information is currently available for this vulnerability. Users should monitor the TiCalc Project Resource for updates and security advisories. Consider migrating to alternative calculator emulation solutions if a patch is not forthcoming.

Workarounds

• Restrict access to the TiEmu binary through file system permissions
• Run TiEmu in a sandboxed or virtualized environment to limit the impact of potential exploitation
• Implement input validation at the system level using wrapper scripts that sanitize ROM parameters before passing them to TiEmu
• Disable or remove TiEmu from systems where calculator emulation is not essential

# Configuration example - Restrict TiEmu execution permissions
chmod 750 /usr/bin/tiemu
chown root:tiemu-users /usr/bin/tiemu

# Create a wrapper script with input validation
cat > /usr/local/bin/tiemu-safe << 'EOF'
#!/bin/bash
# Validate ROM parameter length to prevent buffer overflow
MAX_LENGTH=256
for arg in "$@"; do
    if [ ${#arg} -gt $MAX_LENGTH ]; then
        echo "Error: Parameter too long, potential security risk"
        exit 1
    fi
done
/usr/bin/tiemu "$@"
EOF
chmod 755 /usr/local/bin/tiemu-safe