CVE-2019-14868 in macOS
Summary
by MITRE
In ksh version 20120801, a flaw was found in the way it evaluates certain environment variables. An attacker could use this flaw to override or bypass environment restrictions to execute shell commands. Services and applications that allow remote unauthenticated attackers to provide one of those environment variables could allow them to exploit this issue remotely.
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Analysis
by VulDB Data Team • 10/20/2020
The vulnerability identified as CVE-2019-14868 affects the ksh shell version 20120801 and represents a critical security flaw in environment variable evaluation mechanisms. This issue stems from improper handling of specific environment variables that allows for privilege escalation and command execution bypass. The vulnerability exists within the shell's parsing and evaluation logic where certain environment variables are processed without adequate sanitization or validation, creating an attack surface that can be exploited by remote unauthenticated adversaries.
The technical implementation of this flaw involves the shell's failure to properly validate or sanitize environment variables during the command execution process. When the ksh shell processes environment variables, it does not sufficiently restrict or sanitize inputs that could contain malicious command sequences or payload data. This weakness specifically manifests when the shell encounters environment variables that are designed to be processed as part of command execution paths, allowing attackers to inject arbitrary commands through carefully crafted environment variable values. The vulnerability is particularly dangerous because it operates at the shell level where environment variables are commonly used for configuration and execution context management.
From an operational impact perspective, this vulnerability poses significant risks to systems that rely on ksh for shell operations and services that accept external environment variable inputs. Attackers can exploit this flaw to execute arbitrary commands with the privileges of the affected process, potentially leading to full system compromise. The remote exploitation capability means that systems exposed to unauthenticated network access are particularly vulnerable, as attackers can provide malicious environment variables through various network interfaces without requiring prior authentication. This makes the vulnerability particularly dangerous in web applications, network services, or any system where environment variables are accepted from external sources.
The security implications extend beyond simple command execution to include potential privilege escalation and lateral movement within compromised systems. Systems running ksh versions affected by this vulnerability may be vulnerable to various attack vectors including remote code execution, privilege escalation, and persistent access mechanisms. Organizations using ksh in production environments should consider this vulnerability as a critical threat that requires immediate attention. The flaw's classification aligns with CWE-20, which covers improper input validation, and can be mapped to ATT&CK techniques involving privilege escalation and command execution. Mitigation strategies should include immediate patching of ksh to versions that address the environment variable evaluation flaw, implementation of environment variable whitelisting, and comprehensive monitoring for suspicious environment variable usage patterns. Additionally, system administrators should review and restrict environment variable handling in applications that interface with ksh to prevent exploitation of this vulnerability across the broader system landscape.