CVE-2025-23023 in Discourse
Summary
by MITRE • 02/04/2025
Discourse is an open source platform for community discussion. In affected versions an attacker can carefully craft a request with the right request headers to poison the anonymous cache (for example, the cache may have a response with missing preloaded data). This issue only affects anonymous visitors of the site. This problem has been patched in the latest version of Discourse. Users are advised to upgrade. Users unable to upgrade may disable anonymous cache by setting the `DISCOURSE_DISABLE_ANON_CACHE` environment variable to a non-empty value.
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Analysis
by VulDB Data Team • 02/05/2025
The vulnerability identified as CVE-2025-23023 affects Discourse, an open source platform designed for community discussion and collaboration. This security flaw resides in the platform's handling of anonymous user requests and represents a cache poisoning attack vector that could compromise the integrity of cached content for unauthenticated visitors. The issue specifically targets the anonymous cache mechanism that Discourse employs to improve performance for users who have not logged into the platform. Attackers can exploit this vulnerability by crafting specially formatted HTTP requests with specific headers that manipulate the cache behavior, potentially leading to the injection of malformed or incomplete data into the cache storage.
The technical implementation of this vulnerability stems from insufficient validation of request headers in the cache population logic for anonymous users. When an attacker sends a request with carefully constructed headers, the system processes these requests through the anonymous caching mechanism without proper sanitization or validation checks. This allows the attacker to influence what gets stored in the cache, potentially causing the cache to store responses with missing preloaded data or other corrupted content. The vulnerability is particularly concerning because it specifically targets anonymous visitors who have not authenticated to the system, meaning that any user accessing the platform without logging in could be affected by this cache poisoning attack. This behavior aligns with CWE-1004 which addresses insecure default configurations and improper input validation in web applications.
The operational impact of this vulnerability extends beyond simple data corruption as it creates potential pathways for more sophisticated attacks. Anonymous cache poisoning can lead to information disclosure where attackers might gain access to data that should only be available to authenticated users, or it could enable denial of service conditions if the poisoned cache entries cause system instability. The vulnerability also undermines the trustworthiness of cached content, potentially affecting the platform's performance and reliability for legitimate users who rely on cached responses for faster access. From an attacker's perspective, this vulnerability provides a means to manipulate the user experience for anonymous visitors and could be leveraged as part of broader attack campaigns targeting community platforms. The issue maps to attack techniques in the ATT&CK framework under T1566 for social engineering and T1499 for endpoint detection and response evasion.
The security patch for CVE-2025-23023 addresses the root cause by implementing proper input validation and header sanitization for anonymous requests before they are processed through the caching system. The recommended mitigation strategy involves upgrading to the latest version of Discourse where the vulnerability has been resolved through code-level fixes that ensure proper validation of request headers and cache population logic. For organizations unable to perform immediate upgrades, the workaround of setting the DISCOURSE_DISABLE_ANON_CACHE environment variable provides a temporary solution that disables the vulnerable anonymous caching mechanism entirely. This approach prevents the attack surface from being exploited while maintaining platform functionality, though it may impact performance for anonymous users due to the removal of caching optimizations. Security teams should monitor their Discourse installations for the patched version and implement proper configuration management to ensure that the environment variables are correctly set to prevent exploitation of this vulnerability.