CVE-2023-3997: Splunk SOAR RCE Vulnerability

CVE-2023-3997 Overview

CVE-2023-3997 is a log file poisoning vulnerability affecting Splunk SOAR (Security Orchestration, Automation and Response) versions lower than 6.1.0. This vulnerability allows a third party to send maliciously crafted web requests containing special ANSI escape characters to poison log files. When a terminal user attempts to view these poisoned logs, the ANSI sequences can tamper with the terminal emulator and potentially lead to malicious code execution through the terminal user's actions.

Critical Impact

Attackers can inject malicious ANSI escape sequences into log files, potentially leading to code execution when administrators review logs via terminal, compromising the security of SOAR infrastructure.

Affected Products

• Splunk SOAR (On-Premises) versions prior to 6.1.0
• Splunk SOAR (Cloud) versions prior to 6.1.0

Discovery Timeline

• 2023-07-31 - CVE-2023-3997 published to NVD
• 2024-12-10 - Last updated in NVD database

Technical Details for CVE-2023-3997

Vulnerability Analysis

This vulnerability is classified under CWE-117 (Improper Output Neutralization for Logs) and CWE-116 (Improper Encoding or Escaping of Output). The core issue lies in insufficient sanitization of user-controlled input before it is written to log files. When web requests containing ANSI escape sequences are processed by Splunk SOAR, these special characters are written directly to log files without proper neutralization.

ANSI escape sequences are control characters used to manipulate terminal display properties such as cursor position, text color, and screen clearing. However, certain terminal emulators interpret additional escape sequences that can trigger dangerous behaviors, including executing arbitrary commands or modifying the terminal's title to mislead users.

The attack chain requires user interaction—specifically, a terminal user must view the poisoned logs using commands like cat, less, or tail. This makes the vulnerability particularly insidious as it targets security administrators who routinely review logs as part of incident response or system monitoring activities.

Root Cause

The root cause of CVE-2023-3997 is the failure to properly sanitize or encode ANSI escape sequences and other special characters in user-supplied input before writing them to log files. Splunk SOAR's logging mechanism does not strip or escape these control characters from incoming web requests, allowing them to persist in the log output. This violates the principle of treating log files as trusted data sources, creating an indirect attack vector through log viewers.

Attack Vector

The attack requires local access to the terminal where logs are being viewed, though the initial payload delivery occurs remotely via malicious web requests. An attacker crafts HTTP requests containing ANSI escape sequences in headers, parameters, or body content that gets logged by Splunk SOAR. These sequences remain dormant in the log files until a user with terminal access attempts to view them.

When the logs are displayed in a vulnerable terminal emulator, the escape sequences are interpreted and executed. Depending on the terminal's capabilities, this could result in arbitrary command execution, display manipulation to hide malicious activity, or social engineering attacks through modified terminal output. The attack does not require prior authentication to Splunk SOAR, as the malicious requests simply need to be logged by the system.

Detection Methods for CVE-2023-3997

Indicators of Compromise

• Presence of ANSI escape sequences (hex values \\x1b, \\x9b, or the pattern \033[) in Splunk SOAR log files
• Unusual HTTP requests with control characters in headers, query parameters, or request bodies
• Unexpected terminal behavior when viewing Splunk SOAR logs, such as screen clearing, cursor movement, or color changes

Detection Strategies

• Implement log file scanning to detect ANSI escape sequences and other control characters that should not be present in legitimate log entries
• Monitor incoming web requests for unusual character patterns, particularly escape sequences in HTTP headers and parameters
• Deploy file integrity monitoring on Splunk SOAR log directories to detect unexpected modifications or suspicious content patterns

Monitoring Recommendations

• Configure SIEM rules to alert on HTTP requests containing suspected ANSI escape sequences or control characters
• Implement terminal session recording for administrative access to identify potential exploitation attempts during log review
• Enable verbose logging on web application firewalls to capture and analyze requests with unusual character encodings

How to Mitigate CVE-2023-3997

Immediate Actions Required

• Upgrade Splunk SOAR to version 6.1.0 or later immediately to address this vulnerability
• Review existing log files for signs of ANSI escape sequence injection before upgrading
• Instruct administrators to use safe log viewing methods such as cat -v or less -R which display control characters visibly rather than interpreting them

Patch Information

Splunk has addressed this vulnerability in Splunk SOAR version 6.1.0. The patch implements proper sanitization of log output to prevent ANSI escape sequences from being written to log files. Organizations should apply this update as soon as possible. For detailed patch information, refer to the Splunk Security Advisory SVD-2023-0702.

Workarounds

• Use the cat -v command to view log files, which displays control characters visibly instead of interpreting them
• Configure terminal emulators to disable interpretation of potentially dangerous escape sequences
• Implement a log sanitization layer that strips ANSI escape sequences before logs are written to disk
• Restrict terminal access to Splunk SOAR log files to essential personnel only

# Safe log viewing configuration example
# Use cat with -v flag to show non-printing characters
cat -v /var/log/phantom/phantom_server.log

# Alternatively, use sed to strip ANSI codes when viewing logs
sed 's/\\x1b\[[0-9;]*m//g' /var/log/phantom/phantom_server.log | less

# Configure less to not interpret escape sequences
export LESSSECURE=1
less /var/log/phantom/phantom_server.log