In OpenAI Codex, security researchers have identified two sandbox escape vulnerabilities, one of which allows developers to execute commands on their machine without prompting them. The vulnerabilities, Heapjack and Overpatch, affect different parts of the coding agent's security boundary.
The vulnerability was reported to OpenAI by Accomplish AI on August 12.
According to the researcher, Codex fixed both issues within eight days. The more serious Heapjack vulnerability demonstrated that malicious code could move beyond the restrictions imposed by Codex's sandbox, even when the agent was running as a read-only application.
Heapjack Breaks the Sandbox Boundary
The node_repl component installed with Codex Desktop is targeted by heapjack. Although both OpenAI and untrusted agent code are run in separate JavaScript contexts, both operate within the same Node.js process and share the same memory heap, the separation was not sufficiently effective in preventing a security token from coming into contact with an untrusted environment.
By inspecting the process heap, it was possible to obtain the token generated for the trusted context that remained in shared memory. When the token was obtained, the untrusted code could interact with a native parent process outside the sandbox using the communication channel used by the trusted context. As part of the demonstration of the technique, the researchers launched an application outside of Codex's process tree by utilizing the open command.
A Unix socket as well as other system-level interfaces could also be reached through this access. This demonstration was especially important since it occurred while Codex was running in a strict read-only sandbox mode, where the agent was not expected to have any writing access to the wider system.
The attack could be triggered by a seemingly routine development process.
The researchers demonstrated a scenario in which malicious content contained in a repository, created by a third party, could exploit the vulnerability after the repository was opened in Codex and a query about its code was made.
Overpatch Expands Write Access
Second, a vulnerability known as Overpatch affects the open-source Codex command line utility, and it takes an alternative route outside the sandbox. The vulnerability affects the application_patch tool used by Codex to modify files.
In workspace-write mode, Codex is intended to limit file changes to the project directory. Researchers discovered that apply_patch, instead of expanding write permissions, could expand them based on paths included in patches.
By using a path such as /tmp, the tool was able to treat the root of the file system as an accessible parent directory. In addition to the permission extension, researchers modified .zshrc by creating a symbolic link to the user's home directory so that it would be modified as well.
A successful write was not required for the /tmp entry; its presence extended the permissions granted to the patch operation.
A modified shell configuration resulted in a file modification outside of the permitted workspace without an approval prompt. When a new terminal session was launched, attacker-controlled content ran.
Two Flaws, One Security Boundary Problem
It is important to note that though Heapjack and Overpatch affect different parts of the Codex, both expose weaknesses in the way in which the security boundary of the agent was enforced. In the case of Overpatch, the tool responsible for applying changes also determined the scope from which it had access to data.
In heapjack, trust boundaries were similarly compromised, as the token separating trusted and untrusted execution remained accessible in the same Node.js process and memory space as the untrusted code. The findings suggest that AI coding agents can be restricted in other ways than just controlling their abilities to execute commands.
Untrusted agent activity must also be prevented from influencing the mechanisms that enforce those restrictions by the tools, processes and interfaces surrounding the model. On August 12, 2026, OpenAI was notified of the issues, and they were both addressed within eight days by Accomplish, who stated that Overpatch was addressed in Codex CLI 0.149.0, while Heapjack had been addressed in Codex Desktop build 26.818.21641.
A later statement by OpenAI confirmed that both issues had been resolved in August, and that additional measures were being taken to strengthen file-write controls and expand sandbox testing across platforms. These findings emphasize the security challenges associated with maintaining strong isolation in AI coding environments. Codex Desktop and Codex CLI have been updated to address both vulnerabilities.
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