CVE-2026-11420 Overview
CVE-2026-11420 identifies two path traversal vulnerabilities in the Network Installation Service (NIS) component of Altium Enterprise Server. An unauthenticated network attacker can write arbitrary files to any writable location on the server filesystem and read package archive files from the server. No authentication, session, or credentials are required to exploit either flaw.
The vulnerabilities map to [CWE-22] (Improper Limitation of a Pathname to a Restricted Directory). Altium 365 cloud deployments are not affected because the Network Installation Service is not part of the cloud offering. Only on-premises Altium Enterprise Server installations exposing NIS are at risk.
Critical Impact
Unauthenticated arbitrary file write and read across the server filesystem, escalatable to remote code execution under the NIS service account and disclosure of deployment package contents.
Affected Products
- Altium Enterprise Server (on-premises deployments running the Network Installation Service)
- Network Installation Service (NIS) component bundled with Altium Enterprise Server
- Altium 365 cloud deployments are NOT affected
Discovery Timeline
- 2026-06-05 - CVE-2026-11420 published to NVD
- 2026-06-05 - Last updated in NVD database
Technical Details for CVE-2026-11420
Vulnerability Analysis
The Network Installation Service exposes endpoints that accept file paths from network clients without authentication. Two distinct path traversal flaws exist in how NIS resolves these supplied paths. The first flaw permits arbitrary file write to any directory the service account can access. The second flaw permits arbitrary read of package archive files staged on the server.
Because writes are content-controlled, an attacker can drop files into web-accessible directories served by the same host. Attackers can also overwrite application binaries or configuration files used by NIS or co-resident services. Both write paths convert the file-write primitive into remote code execution in the context of the NIS service account. The read primitive discloses deployment package contents, including any embedded secrets, license material, or proprietary design data shipped to client installations.
Root Cause
The root cause is missing canonicalization and validation of client-supplied path components before file operations. Sequences such as ..\ or absolute paths traverse outside the intended package staging directory. Combined with the absence of authentication on the NIS endpoints, any network-reachable attacker can invoke the vulnerable operations directly.
Attack Vector
The attack vector is network-based and requires no user interaction. An attacker sends crafted requests to the NIS listener with traversal sequences targeting either a write or read operation. For code execution, the attacker writes a payload to a web-served path or replaces a binary loaded by a service running on the host. Refer to the Altium Security Advisory for protocol-level technical details.
Detection Methods for CVE-2026-11420
Indicators of Compromise
- Unexpected files appearing in web-accessible directories or installation paths managed by Altium Enterprise Server
- Modifications to NIS binaries, DLLs, or configuration files outside of scheduled maintenance windows
- NIS service account activity launching child processes such as cmd.exe, powershell.exe, or scripting interpreters
- Outbound network connections originating from the NIS service process to non-Altium destinations
Detection Strategies
- Inspect NIS request logs for path components containing .., ..\, ..%2f, or absolute drive references like C:\
- Hash known-good NIS binaries and compare against the live filesystem to detect overwrite-based persistence
- Alert on file creation events in web roots, startup folders, or scheduled task directories attributed to the NIS service account
- Correlate read operations against package archive paths with source IPs that have no prior administrative history
Monitoring Recommendations
- Forward Altium Enterprise Server and Windows Security event logs to a SIEM for centralized review
- Enable file integrity monitoring on Altium installation directories, web roots, and service configuration files
- Monitor process lineage for the NIS service account and flag any non-Altium child processes
- Track network connections to the NIS listener from sources outside the expected administrative network segments
How to Mitigate CVE-2026-11420
Immediate Actions Required
- Restrict network access to the Network Installation Service to trusted administrative hosts using host-based firewall rules
- Apply the vendor patch referenced in the Altium Security Advisory as soon as it is available for your version
- Review NIS request logs and filesystem timelines for prior exploitation indicators before returning the service to production
- Rotate any secrets, certificates, or license material that may have been disclosed through the read primitive
Patch Information
Altium has published guidance through its security advisory portal. Administrators should consult the Altium Security Advisory for the fixed Enterprise Server build numbers and upgrade instructions. Migrating affected workloads to Altium 365 is an alternative remediation path, as the cloud offering does not ship the vulnerable NIS component.
Workarounds
- Block inbound network access to the NIS listener at the perimeter and host firewalls until patching is complete
- Stop or disable the Network Installation Service on servers that do not actively distribute installation packages
- Run NIS under a least-privileged service account with no write access to web roots or shared binary directories
- Segment Altium Enterprise Server into a dedicated management VLAN with strict ingress filtering
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
