CVE-2026-0846
📋 TL;DR
This vulnerability in nltk's filestring() function allows attackers to read arbitrary files on the system by providing malicious file paths. It affects applications using nltk version 3.9.2 where user input is passed to this function without proper validation. This can lead to exposure of sensitive system files and configuration data.
💻 Affected Systems
- Natural Language Toolkit (nltk)
⚠️ Manual Verification Required
This CVE does not have specific version information in our database, so automatic vulnerability detection cannot determine if your system is affected.
Why? The CVE database entry doesn't specify which versions are vulnerable (no version ranges provided by the vendor/NVD).
🔒 Custom verification scripts are available for registered users. Sign up free to download automated test scripts.
- Review the CVE details at NVD
- Check vendor security advisories for your specific version
- Test if the vulnerability is exploitable in your environment
- Consider updating to the latest version as a precaution
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise through reading of sensitive files like /etc/shadow, SSH keys, or application secrets, potentially leading to privilege escalation or lateral movement.
Likely Case
Exfiltration of sensitive application configuration files, user data, or system information that could enable further attacks.
If Mitigated
Limited impact with proper input validation and file access restrictions in place.
🎯 Exploit Status
Exploitation is straightforward - simply pass a malicious file path to the vulnerable function. The vulnerability is publicly documented with proof-of-concept examples.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 3.9.3 or later
Vendor Advisory: https://github.com/nltk/nltk/security/advisories
Restart Required: No
Instructions:
1. Update nltk using pip: pip install --upgrade nltk>=3.9.3
2. Verify the update with: pip show nltk
3. Test that the filestring() function now validates input paths properly.
🔧 Temporary Workarounds
Input Validation Wrapper
allCreate a wrapper function that validates file paths before passing to filestring()
def safe_filestring(path):
import os
# Validate path is within allowed directory
allowed_dir = '/safe/path'
abs_path = os.path.abspath(path)
if not abs_path.startswith(allowed_dir):
raise ValueError('Invalid file path')
return original_filestring(path)
Disable Vulnerable Function
allReplace calls to filestring() with alternative safe implementations
# Replace: nltk.util.filestring(user_input)
# With: with open(safe_path, 'r') as f:
# content = f.read()
🧯 If You Can't Patch
- Implement strict input validation to only allow relative paths within a safe directory
- Run application with minimal file system permissions and use chroot/jail environments
🔍 How to Verify
Check if Vulnerable:
Check if nltk version is 3.9.2 and if the application uses filestring() with user inputCheck Version:
python -c "import nltk; print(nltk.__version__)"Verify Fix Applied:
Test that providing absolute paths or traversal sequences to filestring() now fails with validation errors📡 Detection & Monitoring
Log Indicators:
- Failed file access attempts with unusual paths
- Access to sensitive system files from application context
Network Indicators:
- Unusual data exfiltration patterns from application servers
SIEM Query:
source=application_logs AND (path="*../*" OR path="*/etc/*" OR path="*/root/*")