CVE-2011-3145 in mount.ecrpytfs_private
Summary
by MITRE
When mount.ecrpytfs_private before version 87-0ubuntu1.2 calls setreuid() it doesn't also set the effective group id. So when it creates the new version, mtab.tmp, it's created with the group id of the user running mount.ecryptfs_private.
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Analysis
by VulDB Data Team • 09/06/2023
The vulnerability described in CVE-2011-3145 represents a critical privilege escalation issue within the ecryptfs filesystem mounting mechanism on Ubuntu systems. This flaw exists in the mount.ecryptfs_private utility, which is responsible for handling encrypted filesystem mounting operations. The vulnerability stems from improper privilege management during the execution of setreuid() system calls, specifically the failure to properly set the effective group ID alongside the user ID. This oversight creates a significant security gap that allows malicious users to manipulate file permissions and potentially gain elevated privileges within the system.
The technical implementation of this vulnerability occurs at the kernel system call level where the mount.ecryptfs_private utility fails to synchronize the effective group ID with the real group ID during privilege transitions. When the utility executes setreuid() without also calling setregid(), it leaves the effective group ID unchanged, maintaining the original group membership of the calling process. This behavior becomes problematic when the utility creates temporary files such as mtab.tmp during the mounting process, as these files inherit the group ID of the user who executed the mount command rather than the appropriate system group. The vulnerability is classified under CWE-256, which deals with incomplete privilege management, and specifically relates to improper handling of group IDs in privilege escalation scenarios.
The operational impact of this vulnerability extends beyond simple privilege escalation to potentially enable unauthorized file system modifications and data access. When mount.ecryptfs_private creates the mtab.tmp file with the user's group ID, it creates a situation where the file permissions may be manipulated by the user to gain access to restricted resources. This flaw allows an attacker to potentially overwrite or corrupt system configuration files that are normally protected by proper group permissions. The vulnerability particularly affects systems running Ubuntu versions prior to 87-0ubuntu1.2 where the fix was implemented, making it a widespread concern for legacy systems that have not been properly updated. This issue aligns with ATT&CK technique T1068 which covers privilege escalation through improper privilege management, and T1059 which involves the use of system utilities for malicious purposes.
The recommended mitigation strategy involves applying the security patch released by Ubuntu in version 87-0ubuntu1.2, which properly implements setregid() alongside setreuid() to ensure that both user and group IDs are correctly synchronized during privilege transitions. System administrators should also implement comprehensive monitoring of the mount.ecryptfs_private utility and its file creation patterns to detect potential exploitation attempts. Additionally, organizations should conduct regular security audits to verify that all system utilities properly handle privilege transitions and that no other similar vulnerabilities exist within the filesystem mounting infrastructure. The fix addresses the root cause by ensuring that effective group IDs are properly managed during the execution context transition, preventing the creation of files with incorrect group ownership that could be exploited for privilege escalation or data manipulation attacks.