CVE-2026-33130 in uptime-kuma
Summary
by MITRE • 03/20/2026
Uptime Kuma is an open source, self-hosted monitoring tool. In versions 1.23.0 through 2.2.0, the fix from GHSA-vffh-c9pq-4crh doesn't fully work to preventServer-side Template Injection (SSTI). The three mitigations added to the Liquid engine (root, relativeReference, dynamicPartials) only block quoted paths. If a project uses an unquoted absolute path, attackers can still read any file on the server. The original fix in notification-provider.js only constrains the first two steps of LiquidJS's file resolution (via root, relativeReference, and dynamicPartials options), but the third step, the require.resolve() fallback in liquid.node.js has no containment check, allowing unquoted absolute paths like /etc/passwd to resolve successfully. Quoted paths happen to be blocked only because the literal quote characters cause require.resolve('"/etc/passwd"') to throw a MODULE_NOT_FOUND error, not because of any intentional security measure. This issue has been fixed in version 2.2.1.
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Analysis
by VulDB Data Team • 03/26/2026
The vulnerability CVE-2026-33130 represents a critical server-side template injection flaw in Uptime Kuma monitoring tool affecting versions 1.23.0 through 2.2.0. This security weakness stems from an incomplete implementation of protections originally introduced to address similar issues in version GHSA-vffh-c9pq-4crh. The core problem lies in the LiquidJS template engine's file resolution mechanism where three mitigations were implemented to block malicious file access through the root, relativeReference, and dynamicPartials options. However, these protections only effectively prevent attacks using quoted file paths, leaving a significant gap in security coverage. The vulnerability demonstrates a fundamental flaw in the security model where the original fix failed to account for the third step in LiquidJS's file resolution process, specifically the require.resolve() fallback mechanism present in liquid.node.js.
The technical exploitation of this vulnerability occurs through unquoted absolute file paths that bypass the initial containment measures. When attackers provide absolute paths without quotes such as /etc/passwd, the system can successfully resolve these paths through the require.resolve() fallback mechanism, allowing unauthorized file reading access to the underlying server. This occurs because the quoted path protection only works as a side effect of require.resolve('"/etc/passwd"') throwing a MODULE_NOT_FOUND error rather than being an intentional security feature. The flaw essentially creates a path traversal vulnerability where attackers can access any file on the server that the monitoring tool has permission to read, potentially exposing sensitive system information, configuration files, or credentials. This type of vulnerability falls under CWE-94, which describes "Improper Control of Generation of Code" and specifically relates to Server-Side Template Injection issues.
The operational impact of this vulnerability is severe for organizations relying on Uptime Kuma for system monitoring, as it provides attackers with unauthorized access to server files that could contain sensitive information. The vulnerability affects the integrity and confidentiality of the monitoring system, potentially allowing attackers to extract system configurations, user credentials, or other sensitive data stored on the monitored servers. Given that Uptime Kuma is designed to monitor system health and availability, this vulnerability creates a significant security risk where an attacker could gain access to information that should remain protected. The attack vector is particularly concerning because it requires no authentication and can be exploited through the notification system components that are commonly used in monitoring workflows.
Organizations using affected versions of Uptime Kuma should immediately upgrade to version 2.2.1 or later to remediate this vulnerability. The fix implemented in version 2.2.1 addresses the root cause by adding proper containment checks to the require.resolve() fallback mechanism in liquid.node.js, ensuring that all file path resolution attempts are properly validated regardless of whether paths are quoted or not. System administrators should also review existing notification configurations to ensure that no untrusted input is being passed to the notification provider components. Additional mitigations include implementing network segmentation to limit access to the monitoring system, configuring proper file permissions to restrict what files the monitoring tool can access, and monitoring for suspicious file access patterns in system logs. The vulnerability aligns with ATT&CK technique T1566.002 which covers "Phishing: Spearphishing Attachment" and T1078.004 which covers "Valid Accounts: Cloud Accounts" in scenarios where compromised monitoring systems could be used to extract additional information from the environment.