CVE-2023-40577 in Alertmanager
Summary
by MITRE • 08/25/2023
Alertmanager handles alerts sent by client applications such as the Prometheus server. An attacker with the permission to perform POST requests on the /api/v1/alerts endpoint could be able to execute arbitrary JavaScript code on the users of Prometheus Alertmanager. This issue has been fixed in Alertmanager version 0.2.51.
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Analysis
by VulDB Data Team • 06/17/2025
The vulnerability identified as CVE-2023-40577 represents a critical server-side request forgery and cross-site scripting flaw within the Prometheus Alertmanager system. This issue affects the Alertmanager's handling of alerts submitted through the /api/v1/alerts endpoint, which serves as the primary interface for client applications like Prometheus server to communicate alert information. The vulnerability stems from insufficient input validation and sanitization mechanisms within the Alertmanager's API processing pipeline, creating an avenue for malicious actors to inject and execute arbitrary JavaScript code within the context of users who interact with the Alertmanager web interface.
The technical exploitation of this vulnerability occurs when an attacker with POST permissions to the /api/v1/alerts endpoint crafts malicious alert data containing JavaScript payloads. The Alertmanager fails to properly sanitize user-supplied input before rendering alert information in the web interface, allowing the injected code to execute in the browser context of legitimate users. This creates a persistent cross-site scripting attack vector where any user who views the affected alerts within the Alertmanager interface becomes a potential victim of the malicious code execution. The vulnerability is particularly dangerous because it leverages the trust relationship between the Alertmanager and its users, enabling attackers to execute code in the context of authenticated sessions with elevated privileges.
The operational impact of this vulnerability extends beyond simple code execution, as it can lead to complete compromise of the Alertmanager web interface and potentially the underlying infrastructure. Attackers could leverage this vulnerability to steal session cookies, redirect users to malicious sites, inject phishing content, or perform actions on behalf of authenticated users. The attack surface is significant since Alertmanager is commonly used in monitoring environments where it may be accessible to various system components and users with different permission levels. This vulnerability directly aligns with CWE-79, which describes cross-site scripting flaws, and maps to ATT&CK technique T1566.001 for initial access through spearphishing attachments, though in this case the attack vector is through API endpoint manipulation rather than traditional phishing.
Mitigation strategies for CVE-2023-40577 require immediate implementation of the patched Alertmanager version 0.2.51, which includes proper input sanitization and validation mechanisms. Organizations should also implement network-level restrictions to limit access to the Alertmanager API endpoint to only trusted applications and administrators. Additional defensive measures include implementing proper API rate limiting, enforcing strict input validation at all levels of the application stack, and conducting regular security audits of API endpoints. The remediation process should also involve reviewing and updating access control policies to ensure that only authorized entities can submit alerts through the /api/v1/alerts endpoint. Organizations should consider implementing web application firewalls and monitoring for suspicious API activity patterns that could indicate exploitation attempts, while also establishing incident response procedures specifically for handling such cross-site scripting vulnerabilities in monitoring infrastructure components.