T03 · Remote Payload Retrieval and Execution
Error
- Location
- SKILL.md:36
- Finding
- Unverified Remote Homebrew Installer Execution## Vulnerability Details **File Location**: `SKILL.md`, line 36 **Vulnerability Type**: Remote payload retrieval and execution **Risk Level**: High **Complete Code Snippet**: ```bash /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)" ``` ### Technical Analysis The Skill instructs the Agent to retrieve a remote shell script and pass the response directly to Bash. The URL references the mutable `HEAD` revision rather than a reviewed and pinned commit, and the command performs no checksum or signature verification before execution. Consequently, the effective code can change after the Skill has been audited. The URL appears to reference Homebrew's official GitHub organization, and the workflow requires the user to agree before installation. These factors reduce accidental or deceptive invocation risk but do not provide payload integrity. A compromised upstream repository or account, malicious upstream modification, or failure in the trusted delivery chain could replace the response with arbitrary shell commands. Homebrew installation is consistent with the Skill's declared purpose. However, immediately executing an unpinned network response is not the minimum-risk mechanism necessary to provide that functionality. ### Attack Path 1. Homebrew is not installed on the target macOS system. 2. The user requests or approves Homebrew installation. 3. The Agent executes the documented `curl` and Bash command. 4. The command downloads the current contents of `install.sh` from mutable `HEAD`. 5. If the upstream source or delivery chain has been compromised or maliciously changed, attacker-controlled shell commands are returned. 6. Bash executes those commands immediately without local review or integrity verification. ### Impact Assessment A substituted installer can execute arbitrary commands with the invoking user's privileges, including reading or modifying user-accessible files ...[truncated 351 chars]
- Remediation
- ## Remediation Suggestions 1. Do not pipe remotely downloaded content directly into a shell. 2. Pin the installer URL to a specific, reviewed Homebrew repository commit instead of `HEAD`. 3. Download the installer to a local file before execution. 4. Verify the file against a trusted SHA-256 digest or a valid cryptographic signature obtained through a separate trusted channel. 5. Display the source, pinned revision, and verification result to the user, then obtain explicit confirmation before running the verified file. 6. Execute with ordinary user privileges unless a specific installation step demonstrably requires elevation; explain and separately confirm any privileged action. 7. If a trustworthy immutable revision and integrity value cannot be maintained, direct the user to Homebrew's official installation documentation rather than automatically executing the installer.