CVE-2021-26619
📋 TL;DR
CVE-2021-26619 is a path traversal vulnerability in BigFileAgent that allows remote attackers to delete arbitrary files on affected systems. This can lead to data loss, service disruption, or system compromise for users running vulnerable versions of the software. The vulnerability is exploitable without authentication, making it a significant threat.
💻 Affected Systems
- BigFileAgent
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Attackers could delete critical system files, causing permanent data loss, system crashes, or full compromise of the server, potentially leading to extended downtime or unauthorized access.
Likely Case
Attackers delete user files or application data, resulting in data loss, service interruptions, or defacement, impacting business operations and user trust.
If Mitigated
With proper network segmentation and access controls, impact is limited to isolated systems, reducing data loss and preventing lateral movement.
🎯 Exploit Status
Exploitation involves crafting malicious requests to traverse directories and delete files; no public proof-of-concept is known, but the simplicity suggests it could be weaponized easily.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Not specified in references; check vendor advisory for exact version.
Vendor Advisory: https://www.krcert.or.kr/krcert/secNoticeView.do?bulletin_writing_sequence=36457
Restart Required: Yes
Instructions:
1. Visit the vendor advisory URL for patch details. 2. Download and apply the latest version of BigFileAgent. 3. Restart the service or system to ensure changes take effect. 4. Verify the fix by testing for the vulnerability.
🔧 Temporary Workarounds
Restrict Network Access
linuxLimit access to BigFileAgent to trusted IP addresses only, reducing exposure to remote attacks.
Use firewall rules: e.g., iptables -A INPUT -p tcp --dport [port] -s [trusted_ip] -j ACCEPT
iptables -A INPUT -p tcp --dport [port] -j DROP
Implement Input Validation
allAdd server-side validation to block path traversal sequences in file deletion requests.
Modify application code to sanitize input: e.g., reject requests containing '../' or absolute paths.
🧯 If You Can't Patch
- Disable or uninstall BigFileAgent if not essential to reduce attack surface.
- Monitor logs and network traffic for suspicious deletion attempts and implement strict access controls.
🔍 How to Verify
Check if Vulnerable:
Test by sending a crafted request with path traversal (e.g., DELETE /files/../../../etc/passwd) to the BigFileAgent endpoint; if it deletes files outside intended directories, it's vulnerable.Check Version:
Check the BigFileAgent version via its interface or configuration files; exact command depends on installation (e.g., grep version /path/to/bigfileagent/config).Verify Fix Applied:
After patching, repeat the test; successful requests should be blocked or return an error, indicating the fix is effective.📡 Detection & Monitoring
Log Indicators:
- Log entries showing file deletion requests with unusual paths like '../' or attempts to access system directories.
- Increased error logs from failed deletion attempts post-patch.
Network Indicators:
- Unusual HTTP DELETE requests to BigFileAgent endpoints with path traversal patterns.
- Spikes in traffic to file deletion APIs from untrusted sources.
SIEM Query:
source="bigfileagent_logs" AND (message="*../*" OR message="DELETE")