CVE-2026-42270 in countly-server
Summary
by MITRE • 10/16/2026
countly-server is the server-side part of Countly, a product analytics solution. Prior to 24.05.50 and 25.03.44, star-rating/images/ and dashboards/images/screenshots/ are among public image and screenshot routes using the local fs storage backend that call getStream and pipe filesystem streams to HTTP responses without an error listener. An unauthenticated request containing a URL-encoded dot can make createReadStream open a directory, emit an asynchronous EISDIR error, and terminate the Node.js process as an unhandled exception, allowing repeated requests to keep the analytics API unavailable. The affected routes also include /appimages/*, /memberimages/*, and */screenshots/*. This issue is fixed in versions 24.05.50 and 25.03.44.
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Analysis
by VulDB Data Team • 10/16/2026
The vulnerability identified in Countly-server prior to versions 24.05.50 and 25.03.44 represents a critical denial of service condition stemming from improper error handling within the application's image processing subsystems. Countly is widely deployed as an open-source product analytics platform, making its availability essential for organizations relying on it for user behavior tracking and business intelligence. The specific flaw resides in several public-facing routes designed to serve static assets, including star ratings, dashboard screenshots, application images, member images, and general screenshot files. These endpoints utilize the local file system storage backend to retrieve content requested by clients. When a request is received, the server attempts to open the specified resource using Node.js's createReadStream function and pipes the resulting stream directly to the HTTP response object for transmission back to the client.
The core technical deficiency lies in the absence of an error event listener on these file streams. In standard asynchronous programming patterns within Node.js, if a stream encounters an unrecoverable error during operation and no handler is attached to catch it, the exception propagates up the call stack as an unhandled promise rejection or fatal process error. This design oversight becomes exploitable when an attacker crafts a request containing a URL-encoded dot sequence that resolves to a directory path rather than a file. Upon receiving such a malformed request, the server attempts to open the specified directory for reading. Since directories cannot be read as streams in this context, the operating system returns an EISDIR error code indicating "Is a Directory." Because the application fails to listen for and handle this asynchronous error event, the exception is not caught by any local try-catch block or stream handler.
The operational impact of this flaw is severe, resulting in the immediate termination of the Node.js process hosting the Countly server instance. Unlike graceful degradation where an API might return a 404 Not Found status for invalid paths, this vulnerability causes a complete crash of the application runtime environment. Consequently, all analytics services provided by that specific node process become unavailable until the service is manually restarted or automatically recovered if a process manager like PM2 detects the exit and restarts it. An unauthenticated attacker can exploit this condition repeatedly to create a persistent denial of service scenario, effectively rendering the entire analytics platform unusable for legitimate users without requiring any form of authentication or privilege escalation. This aligns with CWE-754: Improper Check for Unusual or Exceptional Conditions, as the application fails to validate input against expected file system constraints before attempting resource access.
From a threat intelligence perspective, this vulnerability maps directly to MITRE ATT&CK technique T1499: Endpoint Denial of Service, specifically under the sub-technique of Resource Exhaustion via Crash or Loop. The attacker leverages a single vector to exhaust server resources by forcing repeated restarts and downtime cycles. To mitigate this risk immediately upon upgrading, administrators must ensure they are running Countly-server version 24.05.50 or later for the stable branch, or version 25.03.44 or later for the development branch. These releases include patches that implement proper error handling mechanisms on file streams and likely add input validation to prevent directory traversal or invalid path resolution from triggering fatal exceptions. Additionally, deploying a reverse proxy such as Nginx in front of the Node.js application can provide an additional layer of defense by filtering malformed requests before they reach the application logic, although patching the underlying software remains the primary remediation strategy.