CVE-2020-35512 in D-Bus
Summary
by MITRE • 02/16/2021
A use-after-free flaw was found in D-Bus 1.12.20 when a system has multiple usernames sharing the same UID. When a set of policy rules references these usernames, D-Bus may free some memory in the heap, which is still used by data structures necessary for the other usernames sharing the UID, possibly leading to a crash or other undefined behaviors
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Analysis
by VulDB Data Team • 03/01/2021
The vulnerability identified as CVE-2020-35512 represents a critical use-after-free flaw within the D-Bus message bus system version 1.12.20. This issue manifests specifically when a system environment contains multiple user accounts that share identical user identifiers or UIDs. The fundamental problem arises from how D-Bus handles policy rule evaluation and memory management in multi-user scenarios where user identity conflicts exist. The flaw operates at the intersection of system security architecture and memory safety, creating potential pathways for system instability and security exploitation.
The technical implementation of this vulnerability stems from improper memory deallocation practices within D-Bus's policy evaluation subsystem. When processing access control rules that reference multiple usernames sharing the same UID, the system performs premature memory deallocation operations that leave references to freed memory regions. This occurs because the memory management logic does not properly account for the shared UID scenario where multiple user identities must maintain access to the same underlying data structures. The flaw is categorized under CWE-416 as a use-after-free vulnerability, where memory is accessed after it has been freed, potentially leading to memory corruption and system instability. The vulnerability is particularly dangerous because it can be triggered through legitimate D-Bus communication patterns and does not require special privileges to exploit.
The operational impact of CVE-2020-35512 extends beyond simple system crashes to encompass potential security compromise and service disruption. When the memory corruption occurs, it can result in unpredictable application behavior, denial of service conditions, or in worst-case scenarios, arbitrary code execution. This vulnerability affects systems where user account management practices allow UID reuse, which can occur in containerized environments, virtualized systems, or legacy deployments where multiple user accounts are mapped to the same system UID for compatibility reasons. The attack surface is particularly concerning in enterprise environments where D-Bus is extensively used for inter-process communication, as it could enable attackers to disrupt critical system services or potentially escalate privileges through careful exploitation of the memory corruption.
Mitigation strategies for this vulnerability require immediate system updates to patched versions of D-Bus where the memory management logic has been corrected to properly handle shared UID scenarios. Organizations should implement comprehensive system auditing to identify environments where multiple usernames share UIDs and ensure that these configurations are either corrected or properly isolated from critical D-Bus operations. System administrators should also consider implementing monitoring solutions that can detect anomalous D-Bus behavior patterns that might indicate exploitation attempts. From a defensive perspective, this vulnerability aligns with ATT&CK technique T1059.001 for command and control communications and T1489 for system network disruption, as the memory corruption could be leveraged to create denial of service conditions or potentially enable further attack vectors through system instability. The vulnerability demonstrates the importance of proper memory management in security-critical system components and highlights the need for thorough testing of edge cases in multi-user system environments.