CVE-2020-15778: OpenSSH SCP Command Injection Vulnerability

CVE-2020-15778 Overview

CVE-2020-15778 is a command injection vulnerability in the scp utility of OpenSSH through version 8.3p1. The vulnerability exists in the toremote function within scp.c, where improper handling of the destination argument allows attackers to inject and execute arbitrary commands. This is demonstrated through the use of backtick characters in the destination argument, which the shell interprets and executes.

The OpenSSH vendor has acknowledged this issue but has reportedly stated that they intentionally omit validation of "anomalous argument transfers" because implementing such validation could "stand a great chance of breaking existing workflows."

Critical Impact

Attackers with adjacent network access and low privileges can achieve arbitrary command execution on systems running vulnerable OpenSSH versions, potentially leading to full system compromise with high impact to confidentiality, integrity, and availability.

Affected Products

• OpenBSD OpenSSH through 8.3p1
• NetApp A700s Firmware
• NetApp Active IQ Unified Manager (VMware vSphere)
• NetApp HCI Management Node
• NetApp SolidFire
• NetApp SteelStore Cloud Integrated Storage
• NetApp HCI Compute Node
• NetApp HCI Storage Node
• Broadcom Fabric Operating System

Discovery Timeline

• 2020-07-24 - CVE-2020-15778 published to NVD
• 2025-07-28 - Last updated in NVD database

Technical Details for CVE-2020-15778

Vulnerability Analysis

This vulnerability represents a classic command injection flaw (CWE-78: Improper Neutralization of Special Elements used in an OS Command) in the scp file transfer utility. The toremote function in scp.c fails to properly sanitize or validate destination arguments before passing them to the shell for execution.

When a user specifies a destination path containing shell metacharacters such as backticks (`), the scp utility does not escape or filter these characters. The shell subsequently interprets these metacharacters and executes any commands contained within them. This design decision was intentional by the OpenSSH developers to maintain backward compatibility with existing workflows that may rely on shell expansion features.

The vulnerability requires adjacent network access and some level of user interaction, as the victim must be tricked into executing an scp command with a malicious destination argument or an attacker must have the ability to influence the destination path in automated scripts.

Root Cause

The root cause of CVE-2020-15778 lies in the absence of input validation for shell metacharacters in the destination argument handling within the toremote function. The scp utility relies on the underlying shell to process file paths and remote specifications, which means any embedded shell commands in the destination string will be executed. This architectural decision prioritizes flexibility and backward compatibility over security, allowing shell expansion and command substitution to occur during file transfer operations.

Attack Vector

The attack requires adjacent network access with low privileges and user interaction. An attacker can exploit this vulnerability by crafting a malicious scp destination argument that includes backtick-enclosed commands. When the victim executes scp with this crafted destination, the commands within the backticks are executed with the privileges of the user running scp.

For example, an attacker could provide a destination path such as `malicious_command`@host:/path that, when processed by scp, would cause the shell to execute the embedded command before attempting the file transfer. This attack vector is particularly dangerous in environments where scp commands are generated programmatically using untrusted input, or where users can be socially engineered into copying files to attacker-controlled destinations.

The vulnerability mechanism involves the shell's command substitution feature being triggered during the parsing of the destination argument. When scp constructs the remote command to execute on the target system, it passes the destination through the shell without proper escaping, allowing embedded commands to execute. Technical details and proof-of-concept demonstrations can be found in the GitHub CVE-2020-15778 Repository.

Detection Methods for CVE-2020-15778

Indicators of Compromise

• Unusual scp commands in shell history or process logs containing backtick characters or $() command substitution syntax in destination arguments
• Unexpected child processes spawned from scp process execution
• Anomalous network connections or system changes coinciding with scp file transfer operations
• Log entries showing scp operations with destination paths containing shell metacharacters

Detection Strategies

• Monitor process execution chains for scp spawning unexpected child processes or commands
• Implement command-line argument logging and analysis to detect shell metacharacters in scp destination parameters
• Deploy endpoint detection rules to alert on scp commands containing backticks, $(), or other shell expansion syntax
• Review automated scripts and applications that construct scp commands dynamically for potential injection points

Monitoring Recommendations

• Enable comprehensive audit logging for all scp command executions across the environment
• Implement real-time alerting for scp commands with suspicious destination argument patterns
• Monitor for process genealogy anomalies where scp appears as a parent to unexpected command executions
• Correlate scp activity logs with user behavior analytics to identify abnormal usage patterns

How to Mitigate CVE-2020-15778

Immediate Actions Required

• Audit all automated scripts and applications that use scp to ensure destination arguments are not derived from untrusted user input
• Implement strict input validation for any system that programmatically constructs scp commands
• Consider migrating to sftp or rsync over SSH as more secure alternatives that do not suffer from this command injection vulnerability
• Educate users about the risks of executing scp commands with untrusted destination arguments

Patch Information

The OpenSSH vendor has acknowledged this vulnerability but has not released a traditional patch, as they consider the behavior intentional to maintain backward compatibility. Organizations should refer to the OpenSSH Security Information page for official guidance.

Several distributions have released advisories and mitigations:

• Red Hat Security Advisory RHSA-2024:3166
• Gentoo GLSA 2022-12-06
• NetApp Security Advisory NTAP-20200731-0007

Workarounds

• Use sftp instead of scp for secure file transfers, as it does not pass arguments through the shell in the same manner
• Implement wrapper scripts that validate and sanitize scp destination arguments before execution
• Restrict scp usage through policy controls and provide approved secure alternatives for file transfer operations
• Configure shell environments to log and alert on scp commands containing potentially dangerous metacharacters

# Example: Use sftp as a secure alternative to scp
# Instead of: scp file.txt user@host:/path
sftp user@host <<EOF
put file.txt /path/
EOF

# Or use rsync over SSH for more robust file transfers
rsync -avz -e ssh file.txt user@host:/path/