CVE-2011-1089 in C Library
Summary
by MITRE
The addmntent function in the GNU C Library (aka glibc or libc6) 2.13 and earlier does not report an error status for failed attempts to write to the /etc/mtab file, which makes it easier for local users to trigger corruption of this file, as demonstrated by writes from a process with a small RLIMIT_FSIZE value, a different vulnerability than CVE-2010-0296.
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Analysis
by VulDB Data Team • 11/02/2021
The vulnerability identified as CVE-2011-1089 resides within the GNU C Library implementation where the addmntent function fails to properly handle error conditions when attempting to write to the /etc/mtab file. This function serves as a critical component in system administration operations, particularly when managing filesystem mount points and maintaining the mount table that tracks currently active filesystems. The flaw manifests in glibc versions 2.13 and earlier, where the system does not adequately report error status codes when write operations to /etc/mtab fail, creating a dangerous scenario for system integrity.
The technical nature of this vulnerability stems from the function's inability to distinguish between successful and failed write operations to the mount table file, which operates under the principle that all system calls should properly report their status to ensure reliable operation. When a process attempts to write to /etc/mtab but encounters an error such as insufficient disk space, permission issues, or resource limitations, the addmntent function continues to operate as if the write was successful. This behavior creates a false sense of operational success while silently failing to update the mount table, leading to potential inconsistencies in the system's understanding of its current filesystem state. The vulnerability becomes particularly dangerous when combined with resource constraints such as small RLIMIT_FSIZE values, which limit the amount of data a process can write, making it easier to trigger the error condition that leads to file corruption.
The operational impact of CVE-2011-1089 extends beyond simple file corruption, creating potential security and stability risks for affected systems. Local users can exploit this weakness to manipulate the mount table in ways that may lead to system instability, incorrect filesystem behavior, or even create opportunities for privilege escalation attacks. When the mount table becomes corrupted, system utilities that rely on accurate mount information may behave unpredictably, potentially causing system crashes or allowing unauthorized access to filesystems. The vulnerability particularly affects systems where mount operations are frequently performed and where multiple processes might attempt to update the mount table simultaneously, increasing the probability of encountering the problematic write failure scenario.
This vulnerability aligns with CWE-248, which addresses the issue of an unchecked return value, and represents a classic example of poor error handling in system libraries that can lead to cascading failures. From an ATT&CK framework perspective, this vulnerability could be leveraged as part of a broader attack chain involving privilege escalation or system compromise, particularly when combined with other weaknesses such as those described in CVE-2010-0296 which addresses similar mount table issues. The flaw demonstrates how seemingly minor library-level issues can have significant implications for system security and reliability, emphasizing the critical importance of robust error handling in foundational system components. Organizations should prioritize updating their glibc implementations to versions that properly handle error conditions for mount table operations, as this vulnerability can be exploited by local users to create persistent system instability or security weaknesses. The recommended mitigation strategy involves immediate patching of affected systems and implementation of monitoring for unusual mount table modifications that might indicate corruption resulting from this vulnerability.