A significant security flaw has been identified in Oracle’s Transparent Network Substrate (TNS) protocol, potentially allowing unauthenticated attackers to access sensitive system memory contents, including environment variables and connection data. This vulnerability, designated as CVE-2025-30733, was addressed by Oracle with patches released on April 15, 2025. The affected versions include Oracle Database Server releases 19.3 through 19.26, 21.3 through 21.17, and 23.4 through 23.7, with a CVSS 3.1 Base Score of 6.5, indicating a medium severity level.
Understanding the Vulnerability
The TNS protocol serves as a critical component in Oracle databases, facilitating communication between clients and servers. The identified vulnerability arises from the TNS listener’s improper handling of memory during connection requests, leading to the exposure of uninitialized memory contents. This flaw can be exploited by sending specific version requests to the TNS listener, prompting it to return data that may include sensitive information.
Discovery and Technical Details
Researchers from Driftnet uncovered this vulnerability while developing protocol analyzers for internet intelligence gathering. By sending version requests using commands like (DESCRIPTION=(CONNECT_DATA=(COMMAND=version))), similar to Oracle’s lsnrctl utility, they observed unexpected data being returned after the standard banner information. This data leakage appears as uninitialized memory reads, varying in the amount of sensitive information depending on recent server memory usage.
Examples of leaked data include Windows environment variables such as USERDOMAIN=WORKGROUP, USERNAME=FIDRSRV$, and Path=C:\ORACLE\19.3.0\DATABASE\bin;C:\ORACLE\19.3.0\CLIENT\bin. The leaked information often shows prefixes like sdp or wss, likely related to Session Description Protocol (SDP) and Web Services Security (WSS) features.
Risk Factors and Exploitability
The exploitability of this vulnerability depends on the configuration of the LOCAL_OS_AUTHENTICATION parameter. When set to OFF, the TNS listener becomes accessible beyond local connections, making the memory leak exploitable by external attackers. Despite Oracle’s default configuration since version 10g limiting external access, researchers identified approximately 40 exposed servers worldwide, primarily running Windows systems on the default listener port 1521.
Mitigation Strategies
To address this vulnerability, Oracle has released patches as part of their April 2025 Critical Patch Update. Database administrators are strongly advised to apply these patches promptly to remediate the issue. Additionally, organizations should ensure that the LOCAL_OS_AUTHENTICATION parameter is properly configured to restrict unauthorized access. Minimizing the external exposure of Oracle TNS services by avoiding unnecessary public internet accessibility is also recommended to reduce the attack surface.
Broader Implications
This discovery underscores the ongoing security challenges associated with legacy network protocols. Oracle’s lsnrctl utility, which has been in use for approximately thirty years, exemplifies how longstanding components can harbor vulnerabilities if not regularly updated and monitored. Security experts emphasize the importance of actively managing and minimizing external attack surfaces to protect against such vulnerabilities.
Conclusion
The identification of CVE-2025-30733 highlights the critical need for vigilant security practices in managing database systems. By promptly applying Oracle’s patches and adhering to recommended configuration settings, organizations can mitigate the risks associated with this vulnerability and safeguard sensitive system information from unauthorized access.
