CVE-2019-9804 in Firefox
Summary
by MITRE
In Firefox Developer Tools it is possible that pasting the result of the 'Copy as cURL' command into a command shell on macOS will cause the execution of unintended additional bash script commands if the URL was maliciously crafted. This is the result of an issue with the native version of Bash on macOS. *Note: This issue only affects macOS. Other operating systems are unaffected.*. This vulnerability affects Firefox < 66.
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Analysis
by VulDB Data Team • 09/07/2023
The vulnerability identified as CVE-2019-9804 represents a critical security flaw within Firefox Developer Tools that exploits a specific interaction between the browser's copy functionality and macOS bash shell behavior. This issue specifically manifests when users paste the output of the 'Copy as cURL' command into a bash terminal on macOS systems, creating a potential vector for arbitrary code execution through carefully crafted malicious URLs. The vulnerability stems from the native bash implementation on macOS, which processes certain characters in URL-encoded data in unexpected ways during command execution. This particular flaw demonstrates how seemingly innocuous developer tools can become attack vectors when they interact with underlying system components that have their own security characteristics and behaviors.
The technical root cause of this vulnerability lies in the improper handling of special characters within URL-encoded data when bash processes command-line arguments. When Firefox generates cURL commands for copying, it includes the full URL as a parameter, but the native macOS bash shell interprets certain URL-encoded sequences as shell metacharacters that trigger unintended command execution. This behavior aligns with CWE-78, which describes improper neutralization of special elements used in OS commands, and specifically relates to CWE-153, which addresses improper handling of special characters in shell commands. The vulnerability operates through a command injection mechanism where the malicious URL contains sequences that bash interprets as shell commands rather than literal URL components, creating a path for arbitrary code execution.
The operational impact of this vulnerability is significant for developers who rely on Firefox Developer Tools for web application testing and debugging. Attackers can craft malicious URLs that, when pasted into bash terminals via the 'Copy as cURL' feature, execute unintended commands on the target system with the privileges of the user running the shell. This creates a sophisticated attack vector that leverages the trust users place in developer tools, making it particularly dangerous in environments where developers frequently copy and paste commands from web browsers. The vulnerability affects Firefox versions prior to 66, representing a window of opportunity for attackers to exploit this issue in environments where users have not yet updated their browser. The attack requires minimal user interaction beyond the normal copy-paste workflow, making it particularly stealthy and effective in social engineering scenarios.
Mitigation strategies for this vulnerability involve both immediate browser updates and operational security measures. Organizations should ensure all Firefox installations are updated to version 66 or later, where the issue has been addressed through improved URL handling in the Developer Tools. Additionally, users should be educated about the potential risks of pasting copied commands into shell environments, particularly when the source of the command is not fully trusted. Security practitioners should implement monitoring for unusual command execution patterns and consider disabling or restricting the 'Copy as cURL' functionality in high-security environments. The ATT&CK framework categorizes this as a technique involving command injection and privilege escalation, with the vulnerability acting as a vector for initial compromise. Organizations should also consider implementing shell command sanitization measures and restricting bash execution in sensitive environments to prevent exploitation of similar issues.