Attacker obtains code execution in proxy VM mitigated

THREATQW23 · Mitigated: Controls in place bring the risk down to an acceptable level. · Defined in catalog.py:3344

Risk: High impact × Medium likelihood = 9 high
After mitigations: High impact × Low likelihood = 6 medium

An attacker that gains code execution in the sd-proxy VM can intercept and modify traffic between the client running in sd-app and the Securedrop instance's journalist interface. An attacker could delete sources, submissions or download encrypted submissions and replies, or send messages to sources. An attacker may also exfiltrate the journalist interface ATHS token.

Threat actors: Nation State / Law Enforcement

Mitigations

Mitigation	Status
qrexec that proxies API requests and responses only to SecureDrop application server MITIGQW19	implemented

Related threats

This threat is part of: Vulnerability introduced in provisioning code THREATQW15

Smaller threats that make up this one:

Privilege escalation (Xen vulnerability) THREATQW11 accepted
Vulnerability in the QubesOS management layer THREATQW27 transferred
Attacker tampers with replies in sd-proxy THREATQW42 accepted
Journalist interface hidden service secret exfiltrated THREATQW39 partially mitigated
Journalist Interface credentials exfiltrated (passphrase, single code, username), and API token THREATQW38 partially mitigated
Adversary exploits gzip parsing to get code execution THREATQW37 accepted

Where it applies

Applies to 1 component in 1 scenario.

sd-proxy Workstation VMs

Workstation: reading submissions · sd-proxy

digraph tm {
    graph [
        fontname = Arial;
        fontsize = 14;
    ]
    node [
        fontname = Arial;
        fontsize = 14;
    ]
    edge [
        fontname = Arial;
        fontsize = 12;
    ]
    nodesep = 1;

    subgraph cluster_boundary_Application_Server {
        graph [
            fontsize = 10;
            fontcolor = black;
            style = dashed;
            color = firebrick2;
            label = <<i>Application Server</i>>;
        ]

        component_Journalist_Interface_Application_Server [
            shape = circle;
            color = black;
            fontcolor = black;
            label = "Journalist\nInterface";
            URL = "component_Journalist_Interface.html";
            tooltip = "Journalist Interface";
            margin = 0.02;
        ]

    }

    subgraph cluster_boundary_SecureDrop_Workstation {
        graph [
            fontsize = 10;
            fontcolor = black;
            style = dashed;
            color = firebrick2;
            label = <<i>SecureDrop Workstation</i>>;
        ]

        subgraph cluster_boundary_Workstation_VMs {
            graph [
                fontsize = 10;
                fontcolor = black;
                style = dashed;
                color = firebrick2;
                label = <<i>Workstation VMs</i>>;
            ]

            component_sd_app__SecureDrop_Client__Workstation_VMs [
                shape = circle;
                color = black;
                fontcolor = black;
                label = "sd-app\n(SecureDrop\nClient)";
                URL = "component_sd_app__SecureDrop_Client_.html";
                tooltip = "sd-app (SecureDrop Client)";
                margin = 0.02;
            ]

            component_sd_gpg_Workstation_VMs [
                shape = circle;
                color = black;
                fontcolor = black;
                label = "sd-gpg";
                URL = "component_sd_gpg.html";
                tooltip = "sd-gpg";
                margin = 0.02;
            ]

            component_sd_log_Workstation_VMs [
                shape = circle;
                color = black;
                fontcolor = black;
                label = "sd-log";
                URL = "component_sd_log.html";
                tooltip = "sd-log";
                margin = 0.02;
            ]

            component_sd_proxy_Workstation_VMs [
                shape = circle;
                color = black;
                fontcolor = black;
                label = "sd-proxy";
                URL = "component_sd_proxy.html";
                tooltip = "sd-proxy";
                margin = 0.02;

                style = "filled";

                fillcolor = "#c0392b";

                fontcolor = "white";

                class = "highlighted";
            ]

            component_sd_viewer__disposable_VMs__Workstation_VMs [
                shape = circle;
                color = black;
                fontcolor = black;
                label = "sd-viewer\n(disposable VMs)";
                URL = "component_sd_viewer__disposable_VMs_.html";
                tooltip = "sd-viewer (disposable VMs)";
                margin = 0.02;
            ]

            component_sys_firewall_Workstation_VMs [
                shape = circle;
                color = black;
                fontcolor = black;
                label = "sys-firewall";
                URL = "component_sys_firewall.html";
                tooltip = "sys-firewall";
                margin = 0.02;
            ]

            component_sys_net_Workstation_VMs [
                shape = circle;
                color = black;
                fontcolor = black;
                label = "sys-net";
                URL = "component_sys_net.html";
                tooltip = "sys-net";
                margin = 0.02;
            ]

        }

    }

    actor_Journalist_ [
        shape = square;
        color = black;
        fontcolor = black;
        label = "Journalist";
        URL = "component_Journalist.html";
        tooltip = "Journalist";
        margin = 0.02;
    ]

    actor_Journalist_ -> component_sd_app__SecureDrop_Client__Workstation_VMs [        color = black;        fontcolor = black;        dir = forward;        label = "1. Use the client";    ]
    component_sd_app__SecureDrop_Client__Workstation_VMs -> component_sd_proxy_Workstation_VMs [        color = black;        fontcolor = black;        dir = forward;        label = "2. Journalist API\nrequest";    ]
    component_sd_proxy_Workstation_VMs -> component_sys_firewall_Workstation_VMs [        color = black;        fontcolor = black;        dir = forward;        label = "3. Route via\nfirewall";    ]
    component_sys_firewall_Workstation_VMs -> component_sys_net_Workstation_VMs [        color = black;        fontcolor = black;        dir = forward;        label = "4. Route to network";    ]
    component_sys_net_Workstation_VMs -> component_Journalist_Interface_Application_Server [        color = black;        fontcolor = black;        dir = forward;        label = "5. Reach the\nJournalist Interface";    ]
    component_Journalist_Interface_Application_Server -> component_sys_net_Workstation_VMs [        color = black;        fontcolor = black;        dir = forward;        label = "6. Encrypted\nsubmissions";    ]
    component_sd_proxy_Workstation_VMs -> component_sd_app__SecureDrop_Client__Workstation_VMs [        color = black;        fontcolor = black;        dir = forward;        label = "7. Relay to client";    ]
    component_sd_app__SecureDrop_Client__Workstation_VMs -> component_sd_gpg_Workstation_VMs [        color = black;        fontcolor = black;        dir = forward;        label = "8. Decrypt";    ]
    component_sd_app__SecureDrop_Client__Workstation_VMs -> component_sd_viewer__disposable_VMs__Workstation_VMs [        color = black;        fontcolor = black;        dir = forward;        label = "9. Open a file";    ]
    component_sd_app__SecureDrop_Client__Workstation_VMs -> component_sd_log_Workstation_VMs [        color = black;        fontcolor = black;        dir = forward;        label = "10. Send logs";    ]
}

Notes

Existing mitigations: - Submissions, messages and replies go through sd-proxy encrypted with the gpg encryption key. - securedrop.Proxy qubes-rpc policy only allows sd-app, and requests from all other AppVMs are denied. - We wrote a qrexec service that proxies API requests only to the Journalist Interface (MITIGQW19). Further mitigations: sd-proxy uses a whonix-workstation template, and may present extra attack surface.

How this threat is matched

Listed for these components. A boundary covers every component inside it.