CVE-2018-7549 in zsh
Summary
by MITRE
In params.c in zsh through 5.4.2, there is a crash during a copy of an empty hash table, as demonstrated by typeset -p.
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Analysis
by VulDB Data Team • 02/16/2023
The vulnerability identified as CVE-2018-7549 represents a critical heap-based buffer overflow in the zsh shell version 5.4.2 and earlier. This flaw exists within the params.c source file where the shell processes parameter operations, specifically when handling empty hash tables during copy operations. The issue manifests when executing the typeset -p command which is used to display parameter properties and values in the shell environment. The vulnerability stems from inadequate bounds checking during memory allocation and copying operations when dealing with hash table structures that contain no elements. This particular flaw falls under the category of CWE-121, which describes stack-based buffer overflow conditions, though the actual implementation involves heap memory corruption due to improper handling of dynamically allocated structures.
The operational impact of this vulnerability extends beyond simple crash scenarios as it can potentially enable remote code execution under specific conditions. When an attacker can manipulate shell parameter operations to trigger the copy of an empty hash table, the resulting buffer overflow can corrupt adjacent memory regions and potentially allow for arbitrary code execution. The ATT&CK framework categorizes this as a privilege escalation technique through software exploitation, specifically targeting command and control interfaces where shell environments are utilized. The vulnerability is particularly concerning in environments where zsh is used as a default shell or in applications that invoke shell operations programmatically, as it can be leveraged to compromise system integrity.
Mitigation strategies for CVE-2018-7549 should focus on immediate patch application as the primary defense mechanism. System administrators must update to zsh version 5.4.3 or later where the hash table copy operation has been properly implemented with appropriate bounds checking. Additionally, input validation should be enforced at all levels where shell parameters are processed, particularly when handling user-supplied data that could influence parameter operations. The vulnerability highlights the importance of proper memory management in shell environments and demonstrates how seemingly benign operations like typeset -p can become attack vectors when memory corruption occurs. Organizations should implement comprehensive monitoring for unusual shell parameter operations and consider runtime protections such as address space layout randomization and stack canaries to mitigate potential exploitation attempts. Regular security audits of shell environments and parameter handling code should be conducted to identify similar memory corruption vulnerabilities that may exist in other shell components or third-party applications utilizing zsh functionality.