CVE-2026-9154

Executive Summary

CVE-2026-9154 is an Arbitrary File Write vulnerability in the Rapid7 InsightConnect Sed Plugin on Linux. This flaw allows an authenticated attacker with high privileges to write attacker-controlled content to arbitrary file paths via the expression parameter. The vulnerability has a CVSS score of 7.1 (High), indicating significant impact on confidentiality, integrity, and availability. The EPSS score is 0.0%, suggesting low exploitation likelihood in the wild, but the lack of a patch makes this a critical risk for affected systems.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a plugin within the Rapid7 InsightConnect platform, which is a proprietary orchestration and automation tool. The risk is limited to organizations using the Sed Plugin on Linux systems.

CVSS Breakdown & Threat Level

• CVSS Score: 7.1 (High)
• Attack Vector: Local (AV:L) – Requires local access to the system.
• Attack Complexity: Low (AC:L) – No special conditions required.
• Privileges Required: High (PR:H) – Attacker must be authenticated with high privileges.
• User Interaction: None (UI:N) – No user action needed.
• Scope: Unchanged (S:U) – Impact is confined to the vulnerable component.
• Confidentiality Impact: High (C:H) – Attacker can read sensitive files.
• Integrity Impact: High (I:H) – Attacker can write arbitrary content.
• Availability Impact: High (A:H) – Could lead to system compromise.

Threat Level: High. While the attack requires high privileges, the ability to write arbitrary files can lead to privilege escalation, persistence, or data corruption.

Deep Dive & Mechanics

The vulnerability exists in the Sed Plugin of Rapid7 InsightConnect. The plugin uses the expression parameter to pass commands to the sed utility on Linux. Due to insufficient input validation, an authenticated attacker can inject path traversal sequences (e.g., ../) or absolute paths to write content to arbitrary locations.

Root Cause: The plugin does not sanitize or restrict the output file path in the expression parameter. For example, a malicious expression like s/old/new/w /etc/cron.d/malicious can write attacker-controlled content to /etc/cron.d/malicious.

Attack Flow:

1. Attacker authenticates to InsightConnect with high privileges.
2. Attacker crafts a Sed expression with a write command (w) pointing to an arbitrary file path.
3. The plugin executes the expression, writing attacker-controlled content to the target file.
4. Attacker can overwrite system files, create cron jobs, or modify configuration files.

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual):

def execute_sed(expression, input_file):
    # No validation on expression
    command = f"sed '{expression}' {input_file}"
    os.system(command)

Patched Code (Conceptual):

import shlex

def execute_sed(expression, input_file):
    # Validate expression does not contain write commands
    if 'w' in expression.split('/')[-1]:
        raise ValueError("Write commands not allowed")
    command = f"sed '{shlex.quote(expression)}' {shlex.quote(input_file)}"
    os.system(command)

Note: Since no official patch is available, the above is a recommended fix.

Exploitation & Lab Setup

Red Team

Prerequisites:

• Access to a Linux system with Rapid7 InsightConnect Sed Plugin installed.
• High-privileged credentials.

Exploitation Steps:

1. Identify the Sed Plugin workflow in InsightConnect.
2. Craft a malicious expression to write to a sensitive file, e.g., /etc/cron.d/backdoor:

   s/old/new/w /etc/cron.d/backdoor
   

3. Execute the workflow with the crafted expression.
4. Verify the file was written.

Example Command (if direct access to plugin):

# Assuming the plugin accepts expression as input
insightconnect-sed --expression "s/old/new/w /tmp/evil.sh" --input /etc/passwd

Blue Team

Detection:

• Monitor for unusual Sed commands with write operations (w flag).
• Audit InsightConnect logs for suspicious expression parameters.
• Use file integrity monitoring (FIM) on critical system files.

Hunting:

• Search for files created by the sed process in unusual locations.
• Check for cron jobs or scripts in /etc/cron.d/ that were not manually added.

Indicators of Compromise (IOCs)

• File Paths: /etc/cron.d/*, /tmp/*.sh, /var/spool/cron/*
• Process: sed with w flag in command line
• Logs: InsightConnect logs containing expression with path traversal or write commands
• Network: Outbound connections from compromised system (if backdoor installed)

Detection Engineering

YARA Rule

rule CVE_2026_9154_Sed_Write {
    meta:
        description = "Detects Sed commands with write operations to arbitrary paths"
        author = "Valters IT"
        date = "2025-04-14"
        cve = "CVE-2026-9154"
    strings:
        $sed_write = /sed\s+.*\s+-e\s+['\"]?.*\/w\s+\/[^'\"]+['\"]?/
        $sed_write2 = /sed\s+.*['\"]?.*\/w\s+\/[^'\"]+['\"]?/
    condition:
        any of them
}

Sigma Rule

title: CVE-2026-9154 Sed Write to Arbitrary File
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects Sed commands with write operations to arbitrary file paths
author: Valters IT
date: 2025-04-14
logsource:
    category: process_creation
    product: linux
detection:
    selection:
        Image|endswith: '/sed'
        CommandLine|contains: 'w /'
    condition: selection
falsepositives:
    - Legitimate use of Sed write commands by administrators
level: high

Suricata Rule

alert tcp any any -> any any (msg:"CVE-2026-9154 Sed Write to Arbitrary File"; flow:to_server,established; content:"sed"; http_uri; content:"w /"; distance:0; within:100; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the Sed Plugin if not required.
2. Restrict access to the plugin to only trusted administrators.
3. Implement input validation on the expression parameter to block write commands.

Long-term Fix:

• Apply the official patch from Rapid7 when available.
• Upgrade to a patched version of InsightConnect.

Workaround:

• Use a custom script that sanitizes the expression parameter before passing it to sed.

Monitoring:

• Enable detailed logging for InsightConnect workflows.
• Set up alerts for any Sed write operations.

Valters IT Signature This report was generated by Valters IT Cyber Threat Intelligence Division.