CVE-2019-20433
📋 TL;DR
CVE-2019-20433 is a buffer over-read vulnerability in GNU Aspell that occurs when processing strings ending with a single null byte in UCS-2 or UCS-4 encoding. This vulnerability allows attackers to read beyond allocated memory boundaries, potentially exposing sensitive information or causing application crashes. Systems using Aspell with UCS-2/UCS-4 encoding configured via environment variables are affected.
💻 Affected Systems
- GNU Aspell
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Information disclosure of adjacent memory contents, potentially exposing sensitive data like passwords or encryption keys, leading to complete system compromise.
Likely Case
Application crash (denial of service) or limited information disclosure from adjacent memory regions.
If Mitigated
Minimal impact with proper memory protections like ASLR and DEP, likely resulting only in application crashes.
🎯 Exploit Status
Exploitation requires ability to set environment variables and trigger Aspell processing with specific encoding.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 0.60.8
Vendor Advisory: http://aspell.net/buffer-overread-ucs.txt
Restart Required: Yes
Instructions:
1. Download Aspell 0.60.8 or later from http://aspell.net. 2. Compile and install following standard build procedures. 3. Restart any applications using Aspell library.
🔧 Temporary Workarounds
Remove UCS encoding configuration
allPrevent use of vulnerable UCS-2/UCS-4 encoding by removing or modifying ASPELL_CONF environment variable
unset ASPELL_CONF
export ASPELL_CONF="encoding=utf-8"
Restrict environment variable access
linuxLimit ability to set ASPELL_CONF environment variable for untrusted users
chmod 644 /etc/environment
set secure environment policies
🧯 If You Can't Patch
- Disable Aspell functionality in applications if not required
- Implement strict environment variable controls and user privilege restrictions
🔍 How to Verify
Check if Vulnerable:
Check Aspell version with 'aspell --version' and verify if below 0.60.8Check Version:
aspell --version | head -1Verify Fix Applied:
Confirm version is 0.60.8 or higher with 'aspell --version'📡 Detection & Monitoring
Log Indicators:
- Application crashes with segmentation faults
- Memory access violation errors in system logs
Network Indicators:
- Not applicable - local vulnerability
SIEM Query:
Process:aspell AND (EventID:1000 OR Signal:SIGSEGV)