CVE-2018-1100 in zsh
Summary
by MITRE
zsh through version 5.4.2 is vulnerable to a stack-based buffer overflow in the utils.c:checkmailpath function. A local attacker could exploit this to execute arbitrary code in the context of another user.
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Analysis
by VulDB Data Team • 02/27/2023
The vulnerability identified as CVE-2018-1100 represents a critical stack-based buffer overflow within the zsh shell utility version 5.4.2 and earlier. This flaw exists within the utils.c source file in the checkmailpath function, which processes mail path configurations. The buffer overflow occurs when zsh handles certain mail path specifications, creating an exploitable condition that allows malicious code execution. The vulnerability specifically affects local attackers who can manipulate mail path configurations to trigger the overflow, potentially executing arbitrary code with the privileges of another user.
The technical implementation of this vulnerability stems from improper bounds checking within the checkmailpath function. When zsh processes mail path specifications, it fails to adequately validate input lengths before copying data into fixed-size buffers on the stack. This oversight creates a classic stack-based buffer overflow condition where malicious input can overwrite adjacent stack memory, potentially corrupting program execution flow. The flaw manifests when the mail path configuration contains specially crafted input that exceeds the allocated buffer space, leading to memory corruption that can be leveraged for code execution.
From an operational perspective, this vulnerability poses significant security risks to systems running affected zsh versions. The local attacker exploitation scenario means that an adversary with access to the system could potentially escalate privileges to execute code as other users, particularly those with different permission levels. The impact extends beyond simple code execution as the vulnerability can be exploited to gain unauthorized access to user accounts, potentially leading to complete system compromise. Systems where zsh is used for mail handling or automated processes are particularly vulnerable, as attackers can manipulate mail path configurations to trigger the exploit.
The vulnerability aligns with CWE-121 Stack-based Buffer Overflow, which specifically addresses buffer overflows occurring in stack memory regions. This classification indicates the attack vector involves overflowing a buffer located on the program stack, making it particularly dangerous for privilege escalation attacks. According to ATT&CK framework, this vulnerability maps to T1068, Local Port/Service Scanning, and T1059, Command and Scripting Interpreter, as attackers would need to establish local access and then execute malicious code through the compromised shell. The exploitability requires local system access but can result in high-impact privilege escalation.
Mitigation strategies for CVE-2018-1100 primarily involve updating to zsh version 5.5 or later, where the buffer overflow has been patched through proper bounds checking implementation. System administrators should prioritize patching affected systems, particularly those running mail services or automated scripts that utilize zsh. Additional defensive measures include implementing strict input validation for mail path configurations, restricting local user access where possible, and monitoring for suspicious mail path manipulations. Security configurations should enforce proper privilege separation and limit the scope of user accounts that can modify shell configurations to minimize potential exploitation surfaces.