CVE-2026-3873 Overview
CVE-2026-3873 is a Use of Hard-coded Credentials vulnerability (CWE-798) affecting Avantra versions prior to 25.3.0. This security flaw allows unauthorized users to access functionality that is not properly constrained by Access Control Lists (ACLs). The vulnerability stems from a legacy built-in user account with hardcoded credentials that can be exploited by attackers to bypass authentication mechanisms.
Critical Impact
Attackers exploiting this vulnerability can leverage hardcoded credentials to access restricted functionality, potentially leading to unauthorized data access and system manipulation without proper authentication.
Affected Products
- Avantra versions before 25.3.0
Discovery Timeline
- 2026-03-13 - CVE CVE-2026-3873 published to NVD
- 2026-03-16 - Last updated in NVD database
Technical Details for CVE-2026-3873
Vulnerability Analysis
This vulnerability involves the presence of hard-coded credentials within Avantra's codebase, specifically related to a legacy built-in user account identified as rtm. Hard-coded credentials represent a significant security weakness because they cannot be changed by administrators and remain consistent across all installations. Once discovered, these credentials can be used by any attacker to gain unauthorized access to the system.
The vulnerability enables attackers to access functionality that should be restricted by Access Control Lists (ACLs), effectively bypassing the intended authorization mechanisms. This network-accessible flaw requires no user interaction or authentication to exploit, making it particularly dangerous in internet-exposed deployments.
Root Cause
The root cause of CVE-2026-3873 is the inclusion of a legacy built-in user account with static, hardcoded credentials embedded within the Avantra application. This design pattern, often implemented during development or for backward compatibility purposes, violates secure coding practices by embedding authentication secrets directly in the application code rather than using configurable authentication mechanisms.
Attack Vector
The attack vector is network-based, allowing remote exploitation without requiring user interaction. An attacker with network access to an Avantra installation can authenticate using the hardcoded credentials associated with the legacy rtm account. Once authenticated, the attacker can access functionality that should be restricted by ACLs, potentially viewing or modifying sensitive data and configurations.
The exploitation process involves identifying an exposed Avantra instance, authenticating with the known hardcoded credentials, and then accessing restricted functionality that bypasses normal access controls. For detailed technical information about the legacy built-in user account, refer to the Avantra Security Notice.
Detection Methods for CVE-2026-3873
Indicators of Compromise
- Authentication attempts or successful logins using the legacy rtm user account
- Unusual access patterns to restricted functionality from the built-in account
- Login events from unexpected IP addresses using the hardcoded credentials
- Audit log entries showing ACL-restricted functionality being accessed without proper authorization
Detection Strategies
- Monitor authentication logs for any use of the legacy rtm built-in user account
- Implement alerting for successful authentications from accounts that should be disabled or non-existent
- Deploy network monitoring to detect exploitation attempts targeting Avantra services
- Review access control logs for anomalous activity patterns indicating ACL bypass
Monitoring Recommendations
- Enable comprehensive audit logging for all authentication events in Avantra
- Configure SIEM rules to alert on authentication attempts using legacy or built-in accounts
- Implement network segmentation to limit exposure of Avantra services
- Regularly review user account listings to identify and disable legacy accounts
How to Mitigate CVE-2026-3873
Immediate Actions Required
- Upgrade Avantra to version 25.3.0 or later immediately
- Audit all existing user accounts and disable or remove any legacy built-in accounts
- Review access logs for any unauthorized access using the rtm account
- Restrict network access to Avantra instances to trusted networks only
Patch Information
Avantra has addressed this vulnerability in version 25.3.0. Organizations running affected versions should upgrade to this version or later as soon as possible. The patch removes or disables the legacy built-in user account with hardcoded credentials. For detailed upgrade instructions and additional security guidance, consult the Avantra Security Notice.
Workarounds
- If immediate patching is not possible, restrict network access to Avantra instances using firewall rules
- Disable or lock the legacy rtm user account if the application allows manual account management
- Implement additional authentication layers such as VPN or IP whitelisting for Avantra access
- Deploy web application firewalls to monitor and block suspicious authentication attempts
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
