CVE-2026-9154: Arbitrary File Write in Rapid7 InsightConnect Sed Plugin

Technical summary

CVE-2026-9154 is an arbitrary file write vulnerability (CWE-22: Improper Limitation of a Pathname to a Restricted Directory) in the Sed Plugin component of Rapid7 InsightConnect running on Linux. The vulnerability exists in how the plugin processes the 'expression' parameter without properly validating or restricting output file paths. An authenticated attacker can manipulate this parameter to write attacker-controlled content to arbitrary locations on the filesystem. The CVSS 3.1 score of 7.1 (HIGH) reflects high integrity impact and low availability impact, with network accessibility and low complexity attack surface, though authentication is required as a prerequisite.

Business impact

Organizations using Rapid7 InsightConnect with the Sed Plugin in production environments face risk of unauthorized modification to critical files. Depending on the attacker's objectives and the files targeted, this could lead to: configuration tampering, application malfunction, credential exposure, or lateral movement into other systems. The requirement for authentication limits the threat to insider threats or attackers who have compromised valid user credentials. For security operations teams relying on InsightConnect for automation, a compromised plugin could poison downstream workflows.

Affected systems

Rapid7 InsightConnect deployments on Linux that include the Sed Plugin are affected. The vulnerability also references GNU sed and Linux kernel as affected products, suggesting the issue may impact sed implementations beyond InsightConnect or have dependencies on specific Linux kernel versions. Organizations should verify their specific InsightConnect version and confirm whether the Sed Plugin is deployed in their instance. The vulnerability is not yet listed in the CISA KEV catalog.

Exploitability

Exploitation requires valid authentication credentials to the InsightConnect platform, which significantly constrains attack surface in properly secured environments. Once authenticated, the attack is straightforward: an attacker simply needs to craft a malicious expression parameter value that writes to a target file path. No complex exploit techniques, race conditions, or user interaction are needed. The low attack complexity (AC:L) and network accessibility (AV:N) mean exploitation is relatively easy for an authenticated user. The primary barrier to exploitation is obtaining valid credentials.

Remediation

Rapid7 should release a patched version of InsightConnect that properly validates and sanitizes the expression parameter, implementing path canonicalization and restricting file write operations to intended directories only. Organizations should apply patches as they become available and verify the patch version through Rapid7's security advisories. Until patches are available, restrict access to InsightConnect to trusted users only, implement principle of least privilege for service accounts, monitor file system changes in directories where InsightConnect operates, and consider disabling the Sed Plugin if not actively used.

Patch guidance

Consult Rapid7's official security advisory for InsightConnect to identify the patched version number and release timeline. Apply patches in a staged manner: first to non-production environments, then to production systems during maintenance windows. Verify that the patched version properly restricts the expression parameter and validate functionality of any workflows that use the Sed Plugin. If Rapid7 provides configuration options to restrict output paths post-patch, enable them. Document the patch application and test critical automation workflows that depend on the Sed Plugin.

Detection guidance

Monitor InsightConnect logs for unusual use of the Sed Plugin, particularly with expression parameters containing file path traversal sequences (../, absolute paths, or suspicious file locations). Track file system changes in directories where InsightConnect operates and its configuration directories, especially unexpected modifications to system files, application binaries, or configuration files. Implement file integrity monitoring (FIM) on critical files and directories. Check for unexpected file creation or modification events correlated with InsightConnect service activity. Network-based detection is limited since this is an authenticated local impact; focus detection efforts on endpoint and application logging.

Why prioritize this

While the CVSS score of 7.1 places this in the HIGH severity category, practical prioritization should account for the authentication requirement. Organizations with strong access controls and minimal InsightConnect users should prioritize this below network-exploitable vulnerabilities, but teams using InsightConnect as a central automation platform should treat it as urgent. The ability to write arbitrary files could serve as a stepping stone for persistence or privilege escalation. Teams that have not yet patched should prioritize this within 2-4 weeks depending on their risk tolerance and the sensitivity of systems where InsightConnect operates.

Risk score, explained

The CVSS 3.1 score of 7.1 reflects: (1) high integrity impact from arbitrary file write capability, (2) low availability impact (the plugin doesn't directly crash or disable services), (3) network-accessible attack surface, (4) low complexity attack requiring no special conditions, but (5) authentication prerequisite that reduces overall exploitability. The score appropriately captures that an insider or credential-compromised attacker can damage system integrity, but acknowledges that external unauthenticated attackers cannot exploit this directly. Organizations with mature access controls may view their risk as lower than the base score suggests.

Frequently asked questions