CVE-2016-20041: Yasr Buffer Overflow Vulnerability

CVE-2016-20041 Overview

CVE-2016-20041 is a buffer overflow vulnerability in Yasr (Yet Another Screen Reader) version 0.6.9-5. This accessibility tool, designed to provide screen reading capabilities for Linux users, contains a critical flaw in its command-line argument handling. Local attackers can exploit this vulnerability by supplying an oversized argument to the -p parameter, resulting in application crashes or arbitrary code execution.

The vulnerability allows attackers to invoke yasr with a crafted payload containing junk data, shellcode, and a manipulated return address to overwrite the stack and trigger code execution. This classic stack-based buffer overflow represents a significant security risk on systems where yasr is installed.

Critical Impact

Local attackers can crash the yasr application or achieve arbitrary code execution by exploiting the buffer overflow in the -p parameter handling, potentially compromising the entire system.

Affected Products

• Yasr 0.6.9-5

Discovery Timeline

• 2026-03-28 - CVE CVE-2016-20041 published to NVD
• 2026-03-30 - Last updated in NVD database

Technical Details for CVE-2016-20041

Vulnerability Analysis

The vulnerability exists in Yasr's command-line argument parsing functionality, specifically when processing the -p parameter. When a user supplies an argument exceeding the allocated buffer size, the application fails to properly validate the input length before copying it into a fixed-size stack buffer. This lack of bounds checking allows an attacker to write beyond the buffer's boundaries, corrupting adjacent memory on the stack.

The local attack vector requires the attacker to have access to execute the yasr binary on the target system. However, no privileges are required to trigger the overflow, and no user interaction is needed beyond the attacker invoking the vulnerable command. The potential impact includes complete compromise of confidentiality, integrity, and availability on the affected system.

Root Cause

The root cause of this vulnerability is improper input validation in the argument handling code. The application uses an unsafe memory copy operation when processing the -p parameter without first verifying that the supplied argument fits within the destination buffer's allocated size. This allows user-controlled data to overflow the stack buffer and overwrite critical stack structures including saved return addresses.

Attack Vector

Exploitation follows a classic stack-based buffer overflow approach:

1. Payload Construction: The attacker crafts an argument containing padding data to fill the buffer, followed by shellcode for code execution
2. Stack Manipulation: The oversized payload overwrites the saved return address on the stack with a pointer to the attacker's shellcode
3. Execution Hijacking: When the vulnerable function returns, execution flows to the attacker-controlled code instead of the legitimate return address
4. Code Execution: The shellcode executes with the privileges of the yasr process

The attack is executed locally by invoking yasr with the malicious -p argument. A proof-of-concept exploit is documented in Exploit-DB #39734.

Detection Methods for CVE-2016-20041

Indicators of Compromise

• Unexpected crashes of the yasr process, particularly with stack corruption error messages
• Presence of yasr processes with abnormally long command-line arguments
• System logs showing segmentation faults or memory access violations related to yasr
• Anomalous process spawning or network connections originating from yasr

Detection Strategies

• Monitor command-line arguments passed to yasr binaries for unusually long -p parameter values
• Implement application whitelisting to detect unauthorized execution of yasr with suspicious arguments
• Deploy endpoint detection solutions capable of identifying buffer overflow exploitation attempts
• Use stack canary and ASLR monitoring to detect exploitation attempts

Monitoring Recommendations

• Enable auditd rules to log all executions of the yasr binary along with their arguments
• Configure syslog to capture application crash events and analyze for buffer overflow patterns
• Implement file integrity monitoring on the yasr binary to detect potential tampering
• Monitor for unusual process behavior following yasr execution

How to Mitigate CVE-2016-20041

Immediate Actions Required

• Remove or disable the vulnerable yasr 0.6.9-5 installation if not required for accessibility needs
• Restrict execution permissions on the yasr binary to only authorized users who require it
• Consider using alternative screen reader solutions until a patched version is available
• Compile yasr from source with stack protection mechanisms enabled (stack canaries, ASLR, NX bit)

Patch Information

No official vendor patch has been identified in the available data. System administrators should consult the YASR Project Homepage for any security updates or announcements. The VulnCheck Advisory for YASR provides additional context on this vulnerability.

Workarounds

• Remove execution permissions from the yasr binary for non-essential users using chmod 700 /usr/bin/yasr
• Implement mandatory access control policies (SELinux/AppArmor) to restrict yasr's capabilities
• Use binary hardening wrappers to apply additional runtime protections to the yasr executable
• Create a wrapper script that validates argument lengths before passing them to the actual yasr binary