CVE-2017-7548 in PostgreSQL
Summary
by MITRE
PostgreSQL versions before 9.4.13, 9.5.8 and 9.6.4 are vulnerable to authorization flaw allowing remote authenticated attackers with no privileges on a large object to overwrite the entire contents of the object, resulting in a denial of service.
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Analysis
by VulDB Data Team • 01/09/2021
The vulnerability identified as CVE-2017-7548 represents a critical authorization flaw within PostgreSQL database systems that affects multiple version branches including 9.4.x before 9.4.13, 9.5.x before 9.5.8, and 9.6.x before 9.6.4. This authorization bypass vulnerability specifically targets the large object functionality within PostgreSQL, creating a scenario where authenticated users without any privileges can manipulate large objects in ways that compromise system integrity and availability. The flaw stems from insufficient access controls during large object operations, particularly when handling the LOB_WRONLY flag during write operations, which allows unauthorized modification of data that should be protected from such access patterns.
The technical implementation of this vulnerability occurs within PostgreSQL's large object management subsystem where the system fails to properly validate access permissions when performing write operations on large objects. When an authenticated user attempts to perform a write operation using the LOB_WRONLY flag, the system does not adequately verify whether the user possesses the necessary privileges to modify the target large object. This creates a condition where any authenticated user can overwrite the contents of any large object within the database, regardless of their assigned permissions or roles. The flaw operates at the database engine level and affects the core authorization mechanisms that govern object access, making it particularly dangerous as it can be exploited by attackers who have minimal database access but wish to cause disruption or data corruption.
The operational impact of CVE-2017-7548 extends beyond simple data integrity concerns to encompass significant availability and confidentiality risks. Remote authenticated attackers can leverage this vulnerability to overwrite large objects, potentially destroying critical data that applications depend upon for operation. This capability directly enables denial of service scenarios where legitimate database operations become impossible due to corrupted large object contents, as the system cannot properly access or process data that has been overwritten by unauthorized modifications. The vulnerability can be exploited to target specific large objects containing application data, configuration information, or critical business data, resulting in cascading failures throughout dependent systems that rely on the database for their operation.
From a cybersecurity perspective, this vulnerability aligns with CWE-284 which describes improper access control mechanisms, and represents a clear violation of the principle of least privilege that should govern database access. The flaw also maps to ATT&CK technique T1078 which covers valid accounts for unauthorized access, as it allows attackers to leverage existing authenticated sessions to perform unauthorized operations. Organizations should immediately implement patch management procedures to upgrade to PostgreSQL versions 9.4.13, 9.5.8, or 9.6.4, which contain the necessary fixes for this authorization bypass. Additional mitigations include implementing strict network segmentation to limit database access, monitoring for unusual large object modification patterns, and conducting regular privilege audits to ensure that only authorized users maintain access to sensitive database objects. The vulnerability underscores the importance of comprehensive access control validation even within authenticated sessions, as it demonstrates that insufficient validation of write operations can lead to severe operational consequences including complete service disruption.