CVE-2026-44127: SEPPmail Email Gateway Path Traversal

CVE-2026-44127 Overview

CVE-2026-44127 is an unauthenticated path traversal vulnerability affecting SEPPmail Secure Email Gateway versions prior to 15.0.4. The flaw resides in the identifier parameter of the /api.app/attachment/preview endpoint. Remote attackers can read arbitrary local files and trigger deletion of files within the targeted directory using the privileges of the api.app process. The weakness is classified under CWE-73: External Control of File Name or Path. No authentication is required to exploit the issue, and the attack vector is network-based.

Critical Impact

Unauthenticated remote attackers can read sensitive files and delete arbitrary content on SEPPmail Secure Email Gateway appliances, compromising email security infrastructure confidentiality and integrity.

Affected Products

• SEPPmail Secure Email Gateway versions prior to 15.0.4
• /api.app/attachment/preview endpoint exposed to network clients
• Deployments running the api.app service component

Discovery Timeline

• 2026-05-08 - CVE-2026-44127 published to NVD
• 2026-05-08 - Last updated in NVD database

Technical Details for CVE-2026-44127

Vulnerability Analysis

The vulnerability stems from improper validation of user-supplied input in the identifier parameter of the /api.app/attachment/preview endpoint. The application uses this parameter to construct file paths without enforcing canonicalization or boundary checks against a permitted directory. Attackers can supply traversal sequences such as ../ to escape the intended attachment preview directory and reference arbitrary locations on the filesystem.

Because the endpoint is reachable without authentication, any network client capable of contacting the gateway can issue malicious requests. Successful exploitation allows reading files accessible to the api.app service account and triggering deletion operations within the targeted directory. The EPSS score of 0.194% reflects current exploitation likelihood projections, though the absence of authentication requirements increases practical risk for internet-exposed appliances.

Root Cause

The root cause is insufficient input validation on the identifier parameter, as captured by [CWE-73]. The application accepts caller-controlled path components and passes them to file system operations without normalizing the resulting path or verifying it remains within an allowed base directory. The handler also performs destructive file operations on resolved paths, extending the impact beyond information disclosure to integrity loss.

Attack Vector

An attacker sends a crafted HTTP request to /api.app/attachment/preview with a manipulated identifier parameter containing directory traversal sequences. The handler resolves the path outside the intended attachment directory and returns the contents of the targeted file. Subsequent requests can be issued to delete files within directories accessible to the api.app process. No credentials, user interaction, or prior foothold are required.

Detailed technical information is available in the SEPPmail Security Release Notes.

Detection Methods for CVE-2026-44127

Indicators of Compromise

• HTTP requests to /api.app/attachment/preview containing path traversal sequences such as ../, ..%2f, or encoded variants in the identifier parameter
• Access log entries showing unauthenticated requests to the attachment preview endpoint from unexpected source addresses
• Unexpected file deletions or missing files in directories accessible to the api.app service account
• Anomalous read access to sensitive system files by the api.app process

Detection Strategies

• Inspect web server and application logs for requests targeting /api.app/attachment/preview with abnormal identifier parameter values
• Deploy web application firewall rules that flag directory traversal patterns in query strings against SEPPmail endpoints
• Correlate filesystem audit events for the api.app process with inbound HTTP request logs to identify exploitation chains

Monitoring Recommendations

• Enable verbose access logging on the SEPPmail gateway and forward logs to a centralized analytics platform
• Monitor file integrity on directories writable by the api.app process to detect unauthorized deletions
• Alert on outbound requests or process behavior anomalies originating from the gateway following suspicious inbound traffic

How to Mitigate CVE-2026-44127

Immediate Actions Required

• Upgrade SEPPmail Secure Email Gateway to version 15.0.4 or later as documented in the vendor release notes
• Restrict network exposure of the management and API endpoints to trusted administrative networks only
• Review web server logs for prior exploitation attempts against /api.app/attachment/preview
• Audit files within directories accessible to the api.app process for unauthorized access or deletion

Patch Information

SEPPmail addressed the vulnerability in version 15.0.4. Patch details are published in the SEPPmail Security Release Notes. Administrators should apply the update following the vendor's standard upgrade procedure and validate gateway functionality after deployment.

Workarounds

• Place the SEPPmail gateway behind a reverse proxy or web application firewall that blocks path traversal patterns in request parameters
• Filter inbound traffic to the /api.app/attachment/preview endpoint at the network perimeter until the patch is applied
• Restrict filesystem permissions on the api.app service account to limit the scope of files reachable through traversal

# Example WAF rule pattern to block traversal sequences
# Reject requests to the vulnerable endpoint containing ../ or encoded variants
SecRule REQUEST_URI "@beginsWith /api.app/attachment/preview" \
  "chain,deny,status:403,id:1004127,msg:'CVE-2026-44127 traversal attempt'"
  SecRule ARGS:identifier "@rx (\.\./|\.\.\\|%2e%2e%2f|%2e%2e/)" "t:lowercase,t:urlDecodeUni"