CVE-2020-15778
📋 TL;DR
CVE-2020-15778 is a command injection vulnerability in the scp client of OpenSSH, allowing attackers to execute arbitrary commands on a remote server by exploiting backticks in the destination argument during file transfers. It affects users of OpenSSH scp through version 8.3p1, particularly those who use scp to copy files to untrusted or compromised servers. The vendor has noted that validation was intentionally omitted to avoid breaking workflows, making this a design flaw.
💻 Affected Systems
- OpenSSH
📦 What is this software?
Openssh by Openbsd
Openssh by Openbsd
Openssh by Openbsd
Solidfire by Netapp
⚠️ Risk & Real-World Impact
Worst Case
Full remote code execution on the server, leading to data theft, system compromise, or lateral movement within the network.
Likely Case
Limited command execution by attackers who can trick users into using scp with malicious destination arguments, potentially resulting in unauthorized access or data exfiltration.
If Mitigated
Minimal impact if scp is avoided in favor of secure alternatives like sftp or rsync over SSH, and user awareness is enforced.
🎯 Exploit Status
Exploitation is straightforward with publicly available proof-of-concept scripts, but requires user interaction (e.g., running scp with a crafted argument).
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: OpenSSH 8.4p1 and later
Vendor Advisory: https://access.redhat.com/errata/RHSA-2024:3166
Restart Required: No
Instructions:
1. Update OpenSSH to version 8.4p1 or later using your package manager (e.g., 'sudo apt update && sudo apt upgrade openssh-client' on Debian/Ubuntu). 2. Verify the update with 'ssh -V'. 3. No restart is needed for the client, but ensure all systems are patched.
🔧 Temporary Workarounds
Use sftp or rsync instead of scp
linuxReplace scp usage with sftp or rsync over SSH, which are not affected by this vulnerability.
sftp user@host:file
rsync -avz -e ssh file user@host:destination
Disable scp client usage via policy
allImplement organizational policies to restrict or monitor scp usage, and educate users on the risks.
🧯 If You Can't Patch
- Enforce strict user awareness training to avoid using scp with untrusted destinations or backtick characters.
- Monitor and log scp commands for anomalous patterns (e.g., backticks in arguments) and implement network segmentation to limit potential damage.
🔍 How to Verify
Check if Vulnerable:
Check the OpenSSH version with 'ssh -V' and compare to affected versions (through 8.3p1). If using scp with a test command like 'scp file user@host:"`echo vulnerable`"' results in command execution, the system is vulnerable.Check Version:
ssh -VVerify Fix Applied:
After patching, run 'ssh -V' to confirm version is 8.4p1 or later, and test with the same scp command to ensure no command injection occurs.📡 Detection & Monitoring
Log Indicators:
- Log entries showing scp commands with backtick characters or unusual arguments in SSH or system logs.
Network Indicators:
- Unusual outbound connections or data transfers triggered by scp sessions to suspicious destinations.
SIEM Query:
Example: 'source="ssh_logs" AND message="*scp*`*"' to detect potential exploitation attempts.🔗 References
- https://access.redhat.com/errata/RHSA-2024:3166
- https://github.com/cpandya2909/CVE-2020-15778/
- https://news.ycombinator.com/item?id=25005567
- https://security.gentoo.org/glsa/202212-06
- https://security.netapp.com/advisory/ntap-20200731-0007/
- https://www.openssh.com/security.html
- https://access.redhat.com/errata/RHSA-2024:3166
- https://github.com/cpandya2909/CVE-2020-15778/
- https://news.ycombinator.com/item?id=25005567
- https://security.gentoo.org/glsa/202212-06
- https://security.netapp.com/advisory/ntap-20200731-0007/
- https://www.openssh.com/security.html
