CVE-2026-11431: Altium Server Path Traversal Vulnerability

CVE-2026-11431 Overview

CVE-2026-11431 is a path traversal vulnerability [CWE-22] in the Projects Service download endpoint shared by Altium Enterprise Server and Altium 365. An authenticated user can supply a crafted path parameter that bypasses validation. The flaw allows arbitrary file reads from the server filesystem, including entire directories returned as archives.

The readable files include service configuration and credential material. Attackers can use this access to gather information enabling further compromise. The issue can be chained with CVE-2026-11424 to reach the cloud-side endpoint. On multi-tenant Altium 365 deployments, the readable configuration exposed credentials shared across services.

Critical Impact
Authenticated attackers can read arbitrary files, including service configuration and credentials, from Altium Enterprise Server and Altium 365, enabling lateral movement and further compromise.

Affected Products

Altium Enterprise Server versions prior to 8.1.1
Altium 365 (cloud service, remediated at the service level)
Altium Projects Service download endpoint

Discovery Timeline

2026-06-05 - CVE-2026-11431 published to NVD
2026-06-08 - Last updated in NVD database

Technical Details for CVE-2026-11431

Vulnerability Analysis

The vulnerability resides in the Projects Service download endpoint shared between Altium Enterprise Server and Altium 365. The endpoint accepts a path parameter intended to identify project resources for download. Validation logic fails to properly sanitize directory traversal sequences supplied by the client.

An authenticated user can submit traversal sequences within the path parameter to escape the intended project directory. The endpoint resolves the manipulated path and returns the targeted file content. When the path references a directory, the service archives and returns the entire contents.

The accessible files include service configuration files and credential material used by backend services. On multi-tenant Altium 365 deployments, shared configuration files expose credentials used across multiple tenants. The vulnerability can be combined with CVE-2026-11424 to access the cloud-side endpoint from unintended contexts.

Root Cause

The root cause is improper limitation of a pathname to a restricted directory [CWE-22]. The download endpoint does not normalize or validate user-supplied path components against an allowlist of project paths. Traversal sequences such as ../ are passed to filesystem APIs without canonicalization checks.

Attack Vector

Exploitation requires network access and valid authenticated credentials with low privileges. The attacker issues an HTTP request to the Projects Service download endpoint with a crafted path parameter. The server returns arbitrary file content or directory archives outside the intended project scope. No user interaction is required.

For technical details on the affected endpoint behavior, see the Altium Security Advisory.

Detection Methods for CVE-2026-11431

Indicators of Compromise

HTTP requests to the Projects Service download endpoint containing path traversal sequences such as ../, ..\, or URL-encoded variants like %2e%2e%2f
Unexpected archive downloads from the Projects Service that include configuration or credential files
Access to filesystem paths outside expected project directories in service logs
Anomalous read patterns from low-privilege authenticated accounts targeting system or configuration paths

Detection Strategies

Inspect Projects Service access logs for path parameters containing traversal patterns or absolute path references
Correlate authenticated user sessions with download volumes that exceed normal project usage baselines
Alert on requests where the resolved server-side file path falls outside the expected project root
Monitor for sequential access attempts probing common configuration file locations

Monitoring Recommendations

Enable verbose request logging on the Altium Enterprise Server Projects Service and forward logs to a central SIEM
Track authentication events alongside download endpoint usage to attribute suspicious activity to specific accounts
Establish baselines for download endpoint behavior and alert on deviations in file types or volumes

How to Mitigate CVE-2026-11431

Immediate Actions Required

Upgrade Altium Enterprise Server to version 8.1.1 or later, which contains the fix for this vulnerability
Confirm that Altium 365 tenants are running the remediated service version through the vendor portal
Rotate any credentials, API keys, or secrets stored in service configuration files that may have been exposed
Audit Projects Service access logs for prior exploitation attempts using path traversal sequences

Patch Information

Altium Enterprise Server is fixed in version 8.1.1. Altium 365 has been remediated at the service level by the vendor, requiring no customer action for the cloud service patch. Review the Altium Security Advisory for the full advisory and version guidance.

Workarounds

Restrict network access to the Projects Service download endpoint to trusted management networks until patching is complete
Reduce the number of authenticated accounts with access to the Projects Service to limit the exploitation surface
Apply a reverse proxy or web application firewall rule that blocks requests containing path traversal sequences in download parameters

bash

# Example WAF rule pattern to block traversal sequences on the download endpoint
# Block requests where the path parameter contains ../ or encoded variants
SecRule REQUEST_URI "@rx /projects/.*/download" \
    "chain,deny,status:403,id:1026114310,msg:'Path traversal attempt on Projects Service'"
    SecRule ARGS|REQUEST_URI "@rx (\.\./|\.\.\\|%2e%2e(/|%2f|\\|%5c))" "t:lowercase,t:urlDecodeUni"