CVE-2026-6815: Casdoor Path Traversal Vulnerability

CVE-2026-6815 Overview

CVE-2026-6815 is an arbitrary file write vulnerability in Casdoor's Local File System storage provider. The flaw stems from insufficient path sanitization in the file upload handler. An authenticated attacker with administrative privileges can perform a Path Traversal attack [CWE-22] against the storage component. The attacker bypasses the application's intended storage sandbox and creates or overwrites arbitrary files on the host filesystem. Successful exploitation can lead to configuration tampering, persistence, or code execution depending on which files the attacker targets.

Critical Impact

An authenticated administrative attacker can write or overwrite arbitrary files on the host filesystem, escaping the Casdoor storage sandbox and potentially compromising system integrity.

Affected Products

• Casdoor identity and access management platform
• Deployments configured with the Local File System storage provider
• Instances exposing administrative file upload endpoints

Discovery Timeline

• 2026-05-11 - CVE-2026-6815 published to NVD
• 2026-05-13 - Last updated in NVD database

Technical Details for CVE-2026-6815

Vulnerability Analysis

Casdoor supports multiple storage backends for user-uploaded content, including a Local File System provider. The provider accepts a file name or destination path supplied through an administrative API. The upload logic does not adequately validate or normalize the supplied path before joining it with the configured storage root.

An authenticated administrator can submit path components such as ../ sequences or absolute paths. The application resolves these components and writes the uploaded content outside the intended storage directory. The attacker controls both the destination path and the file contents, producing an arbitrary file write primitive on the host filesystem.

The attack vector is local because the attacker must hold administrative credentials on the Casdoor instance. Impact is limited by the privileges of the Casdoor service account, but those privileges typically include write access to the application directory and adjacent configuration files.

Root Cause

The Local File System storage provider concatenates user-controlled path segments with the storage root without canonicalizing the result. The code does not verify that the resolved path remains within the configured base directory. This omission allows directory traversal sequences to escape the sandbox.

Attack Vector

An attacker authenticates to Casdoor with an administrative account. The attacker invokes the file upload API and supplies a crafted file name containing path traversal characters or an absolute path. The server writes the file to the attacker-chosen location. Targets include startup scripts, web-accessible directories, cron files, or Casdoor's own configuration to enable persistence or privilege escalation. See the CERT Vulnerability Advisory for additional technical details.

Detection Methods for CVE-2026-6815

Indicators of Compromise

• File upload requests to Casdoor administrative endpoints containing ../, ..\, or absolute path prefixes in the file name parameter
• New or modified files outside the configured Casdoor storage directory created by the Casdoor service account
• Unexpected writes to system locations such as /etc/, /var/spool/cron/, web server document roots, or user home directories originating from the Casdoor process

Detection Strategies

• Inspect Casdoor application logs for upload requests whose target path resolves outside the configured storage root
• Correlate administrative session activity with filesystem write events on the host to identify out-of-sandbox writes
• Apply file integrity monitoring on directories adjacent to the Casdoor storage path and on system configuration directories

Monitoring Recommendations

• Alert on any process owned by the Casdoor service account writing outside its designated storage directory
• Track creation of administrative accounts in Casdoor and review their subsequent upload activity
• Forward Casdoor access and audit logs to a central log store for retention and correlation against filesystem telemetry

How to Mitigate CVE-2026-6815

Immediate Actions Required

• Upgrade Casdoor to the fixed version once published by the maintainers and referenced in the CERT Vulnerability Advisory
• Restrict administrative access to Casdoor to a minimal set of trusted operators and enforce multi-factor authentication on those accounts
• Audit existing Casdoor administrators and rotate credentials for any account that may have been compromised

Patch Information

Refer to the CERT Vulnerability Advisory for the official fix reference and upstream patch details. Apply the vendor-supplied update as soon as it is available in your deployment channel.

Workarounds

• Switch the storage provider from Local File System to a remote object storage backend that does not expose host filesystem paths
• Run the Casdoor process under a dedicated low-privilege service account with write access limited to the storage directory only
• Place Casdoor's storage directory on a separate mount with nosuid and noexec options to reduce the impact of arbitrary writes
• Restrict network access to the Casdoor administrative interface using firewall rules or a reverse proxy allowlist

# Configuration example: restrict the Casdoor service account filesystem scope
# Run Casdoor under a dedicated user with a confined storage path
useradd --system --home /var/lib/casdoor --shell /usr/sbin/nologin casdoor
chown -R casdoor:casdoor /var/lib/casdoor/files
chmod 750 /var/lib/casdoor/files

# systemd unit hardening (example)
# [Service]
# User=casdoor
# Group=casdoor
# ProtectSystem=strict
# ProtectHome=true
# ReadWritePaths=/var/lib/casdoor/files
# NoNewPrivileges=true