CVE-2025-9640 in Red Hat
Summary
by MITRE • 10/15/2025
A flaw was found in Samba, in the vfs_streams_xattr module, where uninitialized heap memory could be written into alternate data streams. This allows an authenticated user to read residual memory content that may include sensitive data, resulting in an information disclosure vulnerability.
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Analysis
by VulDB Data Team • 10/17/2025
The vulnerability identified as CVE-2025-9640 resides within the Samba file sharing software ecosystem, specifically within the vfs_streams_xattr module that handles extended attributes for alternate data streams. This flaw represents a critical information disclosure vulnerability that stems from improper memory management practices during the handling of file streams. The vulnerability affects systems running Samba versions that utilize the streams_xattr virtual file system module, which is commonly employed for supporting Windows-style alternate data streams on Unix-like systems. The security implications are significant as this flaw can be exploited by authenticated users who possess valid credentials to access file systems managed by Samba.
The technical root cause of this vulnerability lies in the improper initialization of heap memory regions when processing alternate data streams through the vfs_streams_xattr module. When files are accessed or modified through Samba's extended attribute handling mechanisms, the module fails to properly initialize memory buffers before writing data into alternate data streams. This uninitialized memory often contains residual data from previous operations, including potentially sensitive information such as passwords, cryptographic keys, session tokens, or other confidential data that may have been previously stored in memory. The flaw manifests as a memory disclosure issue where an attacker can read this uninitialized memory content through legitimate file access operations, effectively creating a side-channel information leakage mechanism.
The operational impact of CVE-2025-9640 extends beyond simple information disclosure as it provides attackers with access to residual data that may contain critical system information. An authenticated attacker can exploit this vulnerability to extract sensitive data from memory locations that should not be accessible through normal file operations. This includes potential exposure of user credentials, system configuration details, application data, or other confidential information that may have been stored in memory prior to the current operation. The vulnerability is particularly concerning in environments where Samba serves as a file server for sensitive data, as it can be leveraged to extract information that could subsequently be used for privilege escalation, lateral movement, or other advanced attack vectors. The fact that this requires only authenticated access makes it particularly dangerous as it can be exploited by insiders or compromised legitimate users.
Mitigation strategies for CVE-2025-9640 should prioritize immediate patching of affected Samba installations, as this represents a critical vulnerability that can be exploited without requiring special privileges beyond legitimate user access. Organizations should implement monitoring for unusual file access patterns that might indicate exploitation attempts, particularly around alternate data stream operations. The vulnerability aligns with CWE-457, which describes the use of uninitialized variables, and can be categorized under ATT&CK technique T1005 for data from local system. System administrators should also consider implementing additional access controls and monitoring for Samba file operations, especially those involving extended attributes. Temporary workarounds may include disabling the streams_xattr module if alternate data stream functionality is not critical to operations, though this may impact system functionality. Regular security assessments and memory analysis of affected systems should be conducted to ensure no residual exploitation has occurred, and network segmentation should be considered to limit potential lateral movement if the vulnerability is exploited.