PYSEC-2026-2857

### Impact A Remote Code Execution (RCE) vulnerability was discovered in Ouroboros. If a user clones a malicious repository and runs Ouroboros commands within that directory, it can lead to arbitrary code execution and potential system takeover.

The vulnerability (CWE-426: Untrusted Search Path & CWE-15: External Control of System Setting) stems from Ouroboros loading the `.env` file from the current working directory. Prior to the patch, execution-affecting environment variables such as `OUROBOROS_CLI_PATH`, `OPENCODE_CLI_PATH`, and other backend selectors were accepted directly from this local `.env`. An attacker could include a malicious script in the repository and point the CLI path variable to it (e.g., `OUROBOROS_CLI_PATH=./malicious_script.sh`). When the user executes a command like `ouroboros init` or any command that instantiates the adapter, the malicious script is executed instead of the intended CLI.

### Patches The vulnerability has been patched in version 0.39.0 via PR #1078. The fix establishes a strict trust boundary by applying a denylist to project-local `.env` loading. It blocks execution-affecting environment variables (such as runtime selectors and CLI path overrides) from being loaded from the project directory. Explicit constructor overrides and trusted user-owned home configurations (`~/.ouroboros/.env`) remain fully functional.

Users are strongly advised to upgrade to version 0.39.0 or later.

### Workarounds If upgrading is not immediately possible, users must carefully inspect any `.env` file inside cloned repositories before running Ouroboros commands to ensure it does not contain unexpected `OUROBOROS_*_CLI_PATH` or `OPENCODE_CLI_PATH` overrides.

### References - GitHub PR: https://github.com/Q00/ouroboros/pull/1078