CVE-2026-29963: Hsclabs Mailinspector Path Traversal

CVE-2026-29963 Overview

CVE-2026-29963 is a path traversal vulnerability in HSC MailInspector version 5.3.3-7. The flaw exists in the /tap/dw.php endpoint, which fails to properly validate the text parameter before constructing file paths. Remote unauthenticated attackers can supply traversal sequences to read arbitrary files from the underlying operating system. This vulnerability is classified under CWE-22 (Improper Limitation of a Pathname to a Restricted Directory).

Critical Impact

Unauthenticated remote attackers can disclose sensitive files including configuration data, credentials, and mail content from affected MailInspector deployments.

Affected Products

• HSC MailInspector 5.3.3-7
• HSC Labs MailInspector (versions sharing the vulnerable /tap/dw.php handler)
• Deployments exposing the MailInspector web interface to untrusted networks

Discovery Timeline

• 2026-05-18 - CVE-2026-29963 published to NVD
• 2026-05-19 - Last updated in NVD database

Technical Details for CVE-2026-29963

Vulnerability Analysis

The vulnerability resides in the /tap/dw.php endpoint of HSC MailInspector. The endpoint accepts a text parameter that is incorporated into a file path used by the application to read or return file contents. The implementation does not normalize the parameter, strip directory traversal sequences such as ../, or constrain access to a designated base directory.

An attacker can craft an HTTP request that supplies relative path components in the text parameter to escape the intended directory. Because the endpoint operates without authentication checks against the supplied value, the entire file system is reachable subject only to the privileges of the web server process. Successful exploitation results in disclosure of sensitive data such as /etc/passwd, application configuration files, mail queue contents, and stored credentials.

Root Cause

The root cause is improper input validation of user-supplied path data. The dw.php handler concatenates the text parameter into a file path operation without canonicalization or allow-list enforcement. PHP file functions then resolve traversal sequences against the server's filesystem, granting access outside the intended document root.

Attack Vector

Exploitation requires only network access to the MailInspector web interface. No authentication, user interaction, or special privileges are needed. An attacker issues a GET or POST request to /tap/dw.php with a text parameter containing traversal sequences pointing to a target file. The server responds with the file contents, completing information disclosure in a single request.

No verified exploit code is published in the referenced disclosure repository as a runnable payload. Technical analysis is available in the GitHub CVE-2026-29963 Analysis.

Detection Methods for CVE-2026-29963

Indicators of Compromise

• HTTP requests to /tap/dw.php containing ../ sequences or URL-encoded variants such as %2e%2e%2f in the text parameter
• Web server access logs showing requests to dw.php with parameter values referencing system paths like /etc/passwd, /proc/self/environ, or application configuration files
• Unusual file read activity by the web server user against directories outside the MailInspector application root

Detection Strategies

• Inspect web server and reverse proxy logs for /tap/dw.php requests with suspicious text parameter content and alert on traversal patterns
• Deploy web application firewall (WAF) rules that flag path traversal signatures targeting PHP endpoints
• Correlate web access logs with filesystem auditing on the MailInspector host to identify unauthorized read access by the web server process

Monitoring Recommendations

• Enable verbose logging on the MailInspector application server and forward logs to a centralized analytics platform for retention and search
• Establish a baseline of legitimate /tap/dw.php parameter values and alert on deviations
• Monitor outbound data volume from the MailInspector host to detect large or repeated file disclosure activity

How to Mitigate CVE-2026-29963

Immediate Actions Required

• Restrict network access to the MailInspector web interface using firewall rules or reverse proxy allow-lists until a patched version is deployed
• Apply WAF rules to block traversal sequences in requests to /tap/dw.php
• Audit web server logs for prior exploitation attempts and rotate any credentials that may have been exposed in readable configuration files

Patch Information

No vendor patch advisory is referenced in the available CVE data. Administrators should monitor the HSC Labs Mail Inspector product page and the GitHub CVE Disclosures Repository for vendor remediation guidance and updated builds.

Workarounds

• Block external access to the /tap/dw.php endpoint at the reverse proxy or web server level if the function is not required for production use
• Run the MailInspector web server process under a least-privilege account that cannot read sensitive system or application files
• Apply filesystem ACLs to restrict the web server user's read access to only the directories required by MailInspector