CVE-2018-1071 in zsh
Summary
by MITRE
zsh through version 5.4.2 is vulnerable to a stack-based buffer overflow in the exec.c:hashcmd() function. A local attacker could exploit this to cause a denial of service.
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Analysis
by VulDB Data Team • 01/12/2020
The vulnerability identified as CVE-2018-1071 represents a critical stack-based buffer overflow flaw within the zsh shell version 5.4.2 and earlier. This vulnerability resides in the exec.c source file within the hashcmd() function, which is responsible for handling command hashing operations within the shell environment. The flaw manifests when the shell processes certain command inputs that trigger the hash command functionality, creating conditions where attacker-controlled data can overflow the allocated stack buffer.
The technical implementation of this vulnerability stems from inadequate bounds checking within the hashcmd() function where string operations occur without proper validation of input lengths. When zsh processes commands that involve hashing mechanisms, particularly those involving command names or paths that exceed predetermined buffer limits, the program fails to enforce proper boundary constraints. This allows malicious input to overwrite adjacent stack memory locations, potentially corrupting the program's execution flow and leading to unpredictable behavior.
From an operational perspective, this vulnerability creates significant risks for local attackers who can exploit the buffer overflow to induce denial of service conditions within the targeted system. The attack requires local system access but does not necessitate elevated privileges, making it particularly concerning for environments where multiple users share system resources. The impact extends beyond simple service disruption as the overflow could potentially be leveraged for more sophisticated attacks if proper exploit mitigations are not in place, though the immediate effect remains denial of service.
The vulnerability aligns with CWE-121 Stack-based Buffer Overflow, which specifically addresses buffer overflows occurring in stack memory regions where insufficient bounds checking allows data to overwrite adjacent memory locations. This classification emphasizes the fundamental nature of the flaw as a memory safety issue that affects the program's ability to maintain proper execution boundaries. From an attack framework perspective, this vulnerability would be categorized under the privilege escalation and denial of service attack patterns within the MITRE ATT&CK framework, specifically relating to techniques that manipulate program execution flow through memory corruption.
Mitigation strategies should prioritize immediate patching of affected zsh installations to version 5.4.3 or later, which contains the necessary fixes for the buffer overflow condition. Additionally, system administrators should implement robust input validation procedures and consider deploying stack protection mechanisms such as stack canaries and address space layout randomization to reduce exploitability. Regular security assessments should verify that no other similar buffer overflow vulnerabilities exist within the shell environment, and monitoring systems should be configured to detect anomalous command execution patterns that might indicate exploitation attempts. Organizations should also review their shell usage policies and ensure that only trusted users have local access to systems running vulnerable versions of zsh.