CVE-2026-40342 Overview
CVE-2026-40342 is a critical path traversal vulnerability in Firebird, an open-source relational database management system. The vulnerability exists in the external engine plugin loader, which concatenates user-supplied engine names into filesystem paths without proper sanitization. This allows authenticated attackers with CREATE FUNCTION privileges to load arbitrary shared libraries from anywhere on the filesystem, achieving remote code execution as the server's OS account.
Critical Impact
An authenticated attacker can achieve full remote code execution on the database server by exploiting improper path handling in the external engine plugin loader, potentially compromising the entire system.
Affected Products
- Firebird versions prior to 5.0.4
- Firebird versions prior to 4.0.7
- Firebird versions prior to 3.0.14
Discovery Timeline
- 2026-04-17 - CVE-2026-40342 published to NVD
- 2026-04-20 - Last updated in NVD database
Technical Details for CVE-2026-40342
Vulnerability Analysis
This vulnerability (CWE-22: Improper Limitation of a Pathname to a Restricted Directory) affects Firebird's external engine plugin loading mechanism. The flaw occurs when the database server processes user-supplied engine names for external functions without filtering path separator characters or parent directory (..) components.
When an authenticated user with CREATE FUNCTION privileges specifies an engine name, Firebird concatenates this value directly into a filesystem path used to locate and load the corresponding shared library. The absence of path normalization or validation enables attackers to break out of the intended plugin directory and reference arbitrary locations on the server's filesystem.
The exploitation is particularly dangerous because the shared library's initialization code executes immediately during the loading process—before Firebird performs any module validation. This means an attacker can place a malicious shared library in any accessible location on the server (e.g., through file upload functionality in another application, or a writable network share) and then trigger its execution through the vulnerable engine loading path.
Root Cause
The root cause is insufficient input validation in the external engine plugin loader. The code responsible for constructing the plugin path fails to sanitize user-controlled input, specifically not filtering out path traversal sequences (..) or path separators (/ or \). This allows the attacker-controlled engine name to escape the designated plugin directory and reference arbitrary filesystem locations.
Attack Vector
The attack requires network access to the Firebird database server and valid credentials with CREATE FUNCTION privileges. An attacker crafts a malicious ENGINE name containing path traversal sequences when creating an external function. This causes the server to load a shared library from an attacker-controlled location, with the library's initialization code executing in the context of the Firebird server process.
The attack flow involves:
- Authenticating to the Firebird server with an account possessing CREATE FUNCTION privileges
- Placing or identifying a malicious shared library in an accessible filesystem location
- Creating a function with a crafted ENGINE parameter containing path traversal sequences
- The server concatenates the malicious path and loads the attacker's library
- Library initialization code executes immediately with server privileges
Detection Methods for CVE-2026-40342
Indicators of Compromise
- Unexpected shared library files appearing in non-standard directories on the database server
- Database audit logs showing CREATE FUNCTION statements with suspicious ENGINE parameters containing path traversal sequences (.., /, \)
- Process monitoring showing the Firebird server process loading libraries from unusual filesystem locations
- Evidence of new or modified user accounts with CREATE FUNCTION privileges
Detection Strategies
- Monitor database audit logs for CREATE FUNCTION statements with ENGINE parameters containing path separators or .. sequences
- Implement file integrity monitoring (FIM) on the Firebird server to detect new or modified shared libraries
- Configure network detection rules to identify suspicious database commands targeting Firebird servers
- Review user privilege assignments to identify unnecessary CREATE FUNCTION grants
Monitoring Recommendations
- Enable comprehensive database auditing for DDL statements, particularly CREATE FUNCTION operations
- Deploy endpoint detection and response (EDR) solutions to monitor shared library loading behavior on database servers
- Establish baseline monitoring for normal plugin loading patterns and alert on deviations
- Monitor for privilege escalation attempts that could grant CREATE FUNCTION access
How to Mitigate CVE-2026-40342
Immediate Actions Required
- Upgrade Firebird to patched versions: 5.0.4, 4.0.7, or 3.0.14 immediately
- Audit all database accounts and revoke unnecessary CREATE FUNCTION privileges
- Review existing functions for suspicious ENGINE parameters that may indicate prior exploitation
- Implement network segmentation to limit access to Firebird servers from untrusted networks
Patch Information
Firebird has released security patches that address this vulnerability. The following versions contain the fix:
Organizations should prioritize upgrading to these patched versions. Additional details about this vulnerability are available in the GitHub Security Advisory GHSA-7pxc-h3rv-r257.
Workarounds
- Restrict CREATE FUNCTION privileges to only essential, trusted database administrators until patches can be applied
- Implement strict network access controls to limit who can connect to Firebird database servers
- Use application-level firewall rules to inspect and block suspicious database commands containing path traversal patterns
- Ensure filesystem permissions prevent untrusted users from writing shared libraries to accessible locations on the server
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
