CVE-2014-10070 in zsh
Summary
by MITRE
zsh before 5.0.7 allows evaluation of the initial values of integer variables imported from the environment (instead of treating them as literal numbers). That could allow local privilege escalation, under some specific and atypical conditions where zsh is being invoked in privilege-elevation contexts when the environment has not been properly sanitized, such as when zsh is invoked by sudo on systems where "env_reset" has been disabled.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 02/10/2023
The vulnerability identified as CVE-2014-10070 represents a critical security flaw in the zsh shell software that existed prior to version 5.0.7. This issue stems from the improper handling of integer variables that are imported from the environment during shell initialization. The flaw manifests when zsh processes environment variables that contain integer values, but instead of treating these values as literal numbers, the shell evaluates them as code, creating a potential pathway for malicious exploitation. This behavior occurs specifically during the shell's startup phase when it imports variables from the environment, making it particularly dangerous in privilege escalation scenarios.
The technical nature of this vulnerability aligns with CWE-94, which describes "Improper Control of Generation of Code" or "Code Injection," where the shell's variable processing mechanism fails to properly sanitize or validate environment inputs before executing them as code. The flaw exploits the trust placed in environment variables that are typically considered safe, but in this case, these variables can contain malicious code that gets executed during shell initialization. The vulnerability requires specific conditions to be exploitable, including scenarios where zsh is invoked in contexts that involve privilege elevation, particularly when used with sudo on systems where the "env_reset" configuration has been disabled, which is considered atypical but not impossible in certain deployment configurations.
The operational impact of this vulnerability is significant, as it can enable local privilege escalation under specific conditions. When zsh is invoked by sudo with an unsanitized environment, an attacker who can control environment variables can inject malicious code that gets executed with elevated privileges. This creates a dangerous scenario where an unprivileged user could potentially execute arbitrary commands with the privileges of the user who invoked sudo, effectively bypassing the security controls that sudo is designed to enforce. The vulnerability is particularly concerning because it leverages legitimate shell functionality in an unexpected way, making it difficult to detect through traditional security monitoring approaches.
Mitigation strategies for this vulnerability primarily involve updating to zsh version 5.0.7 or later, where the problematic variable evaluation behavior has been corrected. System administrators should also implement proper environment sanitization practices, particularly ensuring that the "env_reset" option is enabled in sudo configurations to prevent the propagation of potentially malicious environment variables. Additional protective measures include reviewing sudo configurations to minimize the exposure of environment variables to privilege-elevated processes, implementing strict access controls on shell configurations, and conducting regular security audits to identify and remediate similar issues in other shell components. Organizations should also consider implementing runtime monitoring solutions that can detect anomalous shell behavior and environment variable processing that might indicate exploitation attempts. The vulnerability demonstrates the importance of proper input validation and the principle of least privilege in shell environments, where even trusted components can become attack vectors when not properly secured.