cap_clear - Linux

Overview

cap_clear is a command-line utility designed to clear specific capabilities from a binary executable. Capabilities are special privileges that influence file system and system-wide operations. By removing capabilities, cap_clear enhances the security of an executable by limiting its access to certain actions or resources.

Syntax

cap_clear [-h] [-v] [-n] [-c | -p] [-i | -i8] <file>

Options/Flags

• -h, –help: Display help and usage information.
• -v, –version: Show the version of cap_clear.
• -n, –no-strip: Preserve the executable’s original capabilities while clearing the specified capabilities.
• -c, –capability: Specify the capability to be cleared, using the format CAP_NAME (e.g., CAP_SYS_ADMIN).
• -p, –print-caps: Output the current capabilities of the executable.
• -i, –binary-format: Read the binary executable as a pure binary instead of an ELF (default).
• -i8, –binary-format-64-bit: Read the binary executable as a 64-bit pure binary (compatible with 8-bit architectures).

Examples

Clear CAP_SYS_ADMIN from a binary:

cap_clear -c CAP_SYS_ADMIN binary_name

Clear multiple capabilities:

cap_clear -c CAP_SYS_ADMIN -c CAP_DAC_OVERRIDE binary_name

Print the capabilities of an executable:

cap_clear -p binary_name

Common Issues

• User Permission Error: Ensure you have sufficient privileges to modify the binary executable’s capabilities.
• Invalid Capability Name: Verify that the specified capability name is correct using man capabilities.

Integration

cap_clear can be integrated into automated build pipelines to ensure that executables are deployed with appropriate capabilities. It can also be used in conjunction with other security tools to enforce least-privilege principles.

Related Commands

• lscap: List the capabilities of a binary executable.
• setcap: Set specific capabilities for a binary executable.
• capabilities: Provides detailed information about Linux capabilities.