Oracle TNS Flaw Exposes System Memory to Unauthorized Access
Oracle has addressed a significant security flaw in its Transparent Network Substrate (TNS) protocol, used for database communications, with the release of a patch on April 15, 2025.
The vulnerability, tracked as CVE-2025-30733, could allow unauthenticated remote attackers to access sensitive system memory, including environment variables and connection data, by exploiting a memory leak in the Oracle Database Server’s RDBMS Listener.
The flaw affects Oracle Database Server versions 19.3–19.26, 21.3–21.17, and 23.4–23.7, and has been assigned a CVSS 3.1 Base Score of 6.5, indicating a medium severity risk.
Although the default configuration since Oracle 10g restricts unauthenticated external access, minor changes to these settings can leave systems exposed to attack.
How the Memory Leak Occurs
The vulnerability was discovered by Driftnet researchers during the development of protocol analyzers for internet intelligence gathering.
By sending a version request to the Oracle TNS listener using the command:
text(DESCRIPTION=(CONNECT_DATA=(COMMAND=version)))
—similar to Oracle’s own lsnrctl
(Listener Control Utility)—The researchers observed that, in certain configurations, the server returned not only the expected banner information but also additional, uninitialized memory data.
This data could include sensitive information such as:
- Windows environment variables (e.g.,
USERDOMAIN
,USERNAME
,Path
) - Details about connected clients
- System configuration data
The leak is particularly observable when interacting with a TCPS listener (TNS over SSL/TLS), where the Oracle Database server fails to properly zero memory before responding to connection requests.
The leaked memory often contains prefixes like “sdp” or “wss,” likely related to Session Description Protocol (SDP) and Web Services Security (WSS) features.
Example of a leaked environment variable:
textUSERDOMAIN=WORKGROUP
USERNAME=FIDRSRV$
Path=C:ORACLE19.3.0DATABASEbin;C:ORACLE19.3.0CLIENTbin
Exposure, Impact, and Mitigation
While the vulnerability is not widely exposed by default, researchers identified approximately 40 servers worldwide that were vulnerable, primarily running on Windows with the default listener port 1521.

The exposure depends on the LOCAL_OS_AUTHENTICATION
parameter—if set to OFF
, the listener may be accessible to unauthenticated remote users.
Risk and Exploit Table
Risk Factor | Details |
---|---|
Affected Products | Oracle Database RDBMS Listener (19.3–19.26, 21.3–21.17, 23.4–23.7) |
Impact | Unauthorized access to critical system memory contents |
Exploit Prerequisites | 1. Network access to TNS listener 2. Non-default configuration ( LOCAL_OS_AUTHENTICATION=OFF )3. User interaction required |
CVSS 3.1 Score | 6.5 (Medium) |
Mitigation Steps:
- Apply Oracle’s April 2025 Critical Patch Update immediately.
- Ensure
LOCAL_OS_AUTHENTICATION
is enabled to restrict listener access to local connections only. - Minimize external exposure by preventing Oracle TNS services from being accessible over the public internet.
Lessons for Administrators and the Industry
This incident underscores the ongoing risks posed by legacy network protocols and the importance of minimizing the external attack surface.
Despite Oracle’s rapid response and patch release, organizations must remain vigilant in their configuration and patch management practices.
The most effective defense remains to avoid exposing critical database services to the public internet, especially when legacy components like TNS listeners are involved.
Oracle’s handling of CVE-2025-30733 demonstrates a strong security response, but the episode serves as a reminder that even mature, widely deployed software can harbor undiscovered vulnerabilities for decades.
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