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lib/Claude/Agent/MCP/SDKRunner.pm  view on Meta::CPAN

    # *** SECURITY WARNING ***
    # TMPDIR is user-controllable and NOT validated for trust.
    # KNOWN RISK: An attacker who can set TMPDIR before process startup
    # could influence which socket paths are allowed, potentially enabling
    # connections to attacker-controlled sockets.
    #
    # FOR HIGH-SECURITY DEPLOYMENTS: Set CLAUDE_AGENT_IGNORE_TMPDIR=1
    #
    # Additional mitigations:
    #   1. Set CLAUDE_AGENT_IGNORE_TMPDIR=1 to ignore TMPDIR entirely (RECOMMENDED)
    #   2. Validate socket ownership with stat() before connecting
    #   3. Use only fixed prefixes by not setting TMPDIR
    #   4. Run in a restricted environment where TMPDIR cannot be manipulated
    #   5. Set TMPDIR to a trusted directory (e.g., /tmp) before process startup
    # Only allow TMPDIR when explicitly enabled via CLAUDE_AGENT_ALLOW_TMPDIR=1
    # This is opt-in for stricter security - TMPDIR could be attacker-controlled
    # SECURITY WARNING: NEVER set CLAUDE_AGENT_ALLOW_TMPDIR=1 in untrusted environments
    # or when an attacker could control environment variables before process startup.
    # An attacker could set both CLAUDE_AGENT_ALLOW_TMPDIR=1 and a malicious TMPDIR
    # to redirect socket connections to attacker-controlled locations.
    if ($ENV{TMPDIR} && $ENV{TMPDIR} =~ m{^/} && $ENV{CLAUDE_AGENT_ALLOW_TMPDIR}) {

lib/Claude/Agent/MCP/SDKRunner.pm  view on Meta::CPAN

        die "Invalid tool definition: expected hash with 'name' key\n"
            unless ref $tool eq 'HASH' && defined $tool->{name};
    }

    # Build tool lookup
    my %tool_by_name = map { $_->{name} => $_ } @$tools;

    # Validate socket ownership before connecting (defense-in-depth)
    # This helps detect if an attacker has replaced the socket with one they control
    {
        my @stat_info = stat($socket_path);
        if (@stat_info) {
            my $socket_uid = $stat_info[4];
            if ($socket_uid != $<) {
                die "Security error: socket '$socket_path' is owned by uid $socket_uid, expected uid $< (current user)\n";
            }
        }
        # If stat fails, the socket may not exist yet - let the connect() call handle it
    }

    # Connect to parent socket