CVE-2026-90770: Spug RCE Vulnerability

CVE-2026-90770 Overview

CVE-2026-90770 is a command injection vulnerability in OpenSpug versions up to and including 3.4.0. The flaw resides in the ping_check function, which interpolates user-supplied monitor addresses directly into shell commands without validation. Authenticated users with monitor permissions can send crafted addresses containing shell metacharacters to the /monitor/run_test/ endpoint. The injected payload executes arbitrary commands as the Spug process user. The issue is tracked under CWE-78 (OS Command Injection).

Critical Impact

Authenticated attackers can achieve remote code execution on the Spug server, leading to full compromise of monitoring infrastructure and any credentials or hosts managed through it.

Affected Products

• OpenSpug (spug) versions up to and including 3.4.0
• Spug monitor module (spug_api/apps/monitor/)
• Deployments exposing the /monitor/run_test/ endpoint to authenticated users

Discovery Timeline

• 2026-09-13 - CVE-2026-90770 published to the National Vulnerability Database
• 2026-09-18 - Last updated in NVD database

Technical Details for CVE-2026-90770

Vulnerability Analysis

Spug is an open-source operations and monitoring platform. The monitor subsystem supports a ping-based health check that accepts a target address from the user interface. In versions through 3.4.0, the ping_check implementation in spug_api/apps/monitor/executors.py builds the shell command by concatenating the address string into a subprocess invocation executed through a shell. Because the address field is not validated as a hostname or IP, attackers can supply shell metacharacters such as ;, |, &&, or backticks. The /monitor/run_test/ view forwards the value to the executor without sanitization, giving any authenticated account holding monitor permissions a direct path to command execution.

Root Cause

The root cause is unsafe string interpolation of untrusted input into an OS command executed by a shell. The fix, delivered in commit 97aebf1, introduces ipaddress parsing and structural validation of the address before invoking ping. Rejecting non-IP inputs eliminates the metacharacter injection channel.

Attack Vector

Exploitation requires network access to the Spug API and an authenticated account with monitor permissions. The attacker submits a monitor test containing an address such as 127.0.0.1; <command> to the /monitor/run_test/ endpoint. The Spug backend passes the string through a shell, executing the injected command with the privileges of the Spug application user.

# Security patch in spug_api/apps/monitor/executors.py
 from apps.monitor.utils import handle_notify, handle_trigger_event
 from socket import socket
 import subprocess
+import ipaddress
 import platform
 import requests
 import logging
# Source: https://github.com/openspug/spug/commit/97aebf133e1f9cbb35ccebadab1faedfdfe93f42

The patch imports Python's ipaddress module so the executor can validate the target string as a legitimate IPv4 or IPv6 address before it reaches the shell. The same commit also hardens LDAP filter handling in spug_api/libs/ldap.py by adopting escape_filter_chars.

Detection Methods for CVE-2026-90770

Indicators of Compromise

• HTTP POST requests to /monitor/run_test/ containing shell metacharacters such as ;, |, &, $(, or backticks in the address field.
• Child processes of the Spug application (typically python, gunicorn, or uwsgi) spawning shells (/bin/sh, /bin/bash) that execute unexpected binaries like curl, wget, nc, or chmod.
• Outbound network connections from the Spug host to unfamiliar external hosts shortly after monitor test activity.

Detection Strategies

• Inspect Spug API access logs for run_test requests whose payload address deviates from valid IPv4, IPv6, or DNS hostname syntax.
• Correlate authentication events with monitor test submissions to identify low-privileged accounts triggering the endpoint at unusual rates.
• Use process ancestry telemetry to flag ping invocations that share a parent shell with additional commands.

Monitoring Recommendations

• Enable verbose audit logging on the Spug monitor module and forward it to a central log store for retention and search.
• Alert on any new file writes, cron entries, or SSH key modifications on the Spug application host.
• Baseline outbound traffic from the Spug server and alert on deviations, particularly connections to non-monitored endpoints.

How to Mitigate CVE-2026-90770

Immediate Actions Required

• Upgrade Spug to a release that includes commit 97aebf1 or later, which validates ping targets with ipaddress.
• Rotate all credentials, SSH keys, and API tokens managed through the Spug host, since a successful exploit exposes them to the attacker.
• Audit monitor permissions and remove the role from accounts that do not require it.

Patch Information

The fix is available in the upstream repository at OpenSpug Commit 97aebf1. Additional context is provided in OpenSpug Issue #741 and the VulnCheck Advisory for OpenSpug RCE. Review the changes to spug_api/apps/monitor/executors.py and spug_api/libs/ldap.py before deployment.

Workarounds

• Restrict network access to the Spug management interface using firewall rules or a VPN so only trusted operators can reach /monitor/run_test/.
• Run the Spug process under a dedicated low-privilege account with no shell login and no access to sensitive files or credentials.
• Deploy a reverse proxy rule that rejects requests to the monitor endpoint containing shell metacharacters in the address parameter.

# Example nginx rule to block metacharacters in monitor test payloads
location /monitor/run_test/ {
    if ($request_body ~* "[;&|`$()<>]") {
        return 400;
    }
    proxy_pass http://spug_backend;
}