CVE-2024-53851 in Discourse
Summary
by MITRE • 02/05/2025
Discourse is an open source platform for community discussion. In affected versions the endpoint for generating inline oneboxes for URLs wasn't enforcing limits on the number of URLs that it accepted, allowing a malicious user to inflict denial of service on some parts of the app. This vulnerability is only exploitable by authenticated users. This issue has been patched in the latest stable, beta and tests-passed versions of Discourse. Users are advised to upgrade. Users unable to upgrade should turn off the `enable inline onebox on all domains` site setting and remove all entries from the `allowed inline onebox domains` site setting.
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Analysis
by VulDB Data Team • 09/26/2025
The vulnerability identified as CVE-2024-53851 affects Discourse, an open source platform designed for community discussion and collaboration. This issue resides within the platform's inline onebox functionality, which automatically generates rich previews for URLs posted within discussions. The flaw manifests in the endpoint responsible for processing URL oneboxing operations, where insufficient input validation and resource limitation controls exist. Authentication requirements for exploitation mean that only users with valid credentials can potentially trigger this vulnerability, though the impact on system resources remains significant enough to warrant immediate attention.
The technical implementation of this vulnerability stems from the lack of proper rate limiting and input validation within the URL processing pipeline. When users submit multiple URLs for oneboxing, the system fails to enforce reasonable limits on the quantity of URLs processed in a single request. This absence of boundary controls creates an opportunity for malicious actors to craft requests containing excessive URL parameters, potentially overwhelming the server's processing capabilities and leading to resource exhaustion. The vulnerability aligns with CWE-770, which addresses allocation of resources without proper limits, and represents a classic denial of service scenario where legitimate system resources become unavailable due to excessive consumption.
Operational impact of CVE-2024-53851 extends beyond simple service disruption to potentially compromise the overall stability and performance of Discourse installations. When exploited, the vulnerability can cause significant resource contention, leading to degraded response times, application unresponsiveness, or complete service outages. The attack vector requires authenticated access, which somewhat limits the scope of potential exploitation compared to publicly accessible vulnerabilities, but still poses a substantial risk to organizations relying on Discourse for their community platforms. The impact is particularly concerning in high-traffic environments where multiple users might simultaneously exploit the vulnerability, amplifying the denial of service effects.
Mitigation strategies for this vulnerability involve both immediate remediation and temporary workaround measures. The primary solution requires upgrading to the latest stable, beta, or tests-passed versions of Discourse where the issue has been patched. This upgrade process addresses the root cause by implementing proper input validation and resource limitation controls within the onebox endpoint. Organizations unable to perform immediate upgrades should implement the recommended temporary measures including disabling the `enable inline onebox on all domains` site setting and clearing all entries from the `allowed inline onebox domains` setting. These configurations effectively disable the vulnerable functionality while maintaining system stability. From an ATT&CK framework perspective, this vulnerability maps to techniques involving resource exhaustion and service disruption, with the authenticated access requirement placing it in the category of privilege escalation and denial of service attacks that require initial system access.