CVE-2025-26042 in Kuma
Summary
by MITRE • 03/17/2025
Uptime Kuma >== 1.23.0 has a ReDoS vulnerability, specifically when an administrator creates a notification through the web service. If a string is provided it triggers catastrophic backtracking in the regular expression, leading to a ReDoS attack.
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Analysis
by VulDB Data Team • 01/26/2026
The vulnerability identified as CVE-2025-26042 affects Uptime Kuma versions 1.23.0 and above, presenting a significant security risk through a regular expression denial of service flaw. This issue specifically manifests when administrators utilize the web service to create notifications, creating a critical attack vector that can compromise system availability and performance. The vulnerability stems from improper input validation within the notification creation process, where user-provided strings trigger catastrophic backtracking in regular expression matching algorithms. This type of vulnerability falls under the Common Weakness Enumeration category CWE-400, which specifically addresses improper input validation leading to resource exhaustion. The attack exploits the inherent weakness in how regular expressions handle certain input patterns, causing the system to consume excessive computational resources during pattern matching operations.
The technical implementation of this vulnerability occurs within the notification handling subsystem of Uptime Kuma, where regular expression patterns are used to validate and process user input. When an attacker provides a specially crafted string that triggers the problematic regular expression, the matching engine enters into a state of catastrophic backtracking where it repeatedly evaluates the same input positions multiple times. This behavior causes exponential time complexity in the regular expression engine, leading to significant CPU consumption and potential system unresponsiveness. The operational impact extends beyond simple performance degradation, as this vulnerability can be leveraged to perform denial of service attacks against the monitoring service itself, potentially disrupting critical uptime monitoring operations that organizations rely upon for system availability assurance.
The implications of this vulnerability are particularly severe in production environments where Uptime Kuma serves as a critical monitoring tool for infrastructure health. Attackers can exploit this weakness by crafting malicious input strings that cause the system to enter infinite or near-infinite loops during regular expression processing, effectively consuming all available CPU resources and rendering the notification service unavailable. This attack vector aligns with the ATT&CK framework's T1499.004 technique for network denial of service, specifically targeting the availability aspect of the system's operational integrity. The vulnerability affects the availability and reliability of the monitoring platform, potentially leading to missed alerts and compromised system visibility during critical incidents.
Mitigation strategies for CVE-2025-26042 should focus on immediate patching of affected Uptime Kuma versions, with administrators upgrading to the latest stable release that contains fixed regular expression patterns. Additionally, input validation should be enhanced to sanitize and limit the length of strings processed through regular expressions, implementing rate limiting and input length restrictions to prevent exploitation. Network segmentation and monitoring of notification service endpoints can help detect potential exploitation attempts. Organizations should also consider implementing automated vulnerability scanning processes that can identify and alert on similar regex-related vulnerabilities within their application environments. The fix typically involves rewriting the vulnerable regular expression patterns to eliminate catastrophic backtracking possibilities while maintaining the intended validation functionality. Security teams should conduct thorough testing of patched versions to ensure that the remediation does not introduce new functionality issues or regressions in the notification system's core capabilities.