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Redis is an open source, in-memory database that persists on disk. In versions starting at 2.6 and prior to 7.4.3, An unauthenticated client can cause unlimited growth of output buffers, until the server runs out of memory or is killed. By default, the Redis configuration does not limit the output buffer of normal clients (see client-output-buffer-limit). Therefore, the output buffer can grow unlimitedly over time. As a result, the service is exhausted and the memory is unavailable. When password authentication is enabled on the Redis server, but no password is provided, the client can still cause the output buffer to grow from "NOAUTH" responses until the system will run out of memory. This issue has been patched in version 7.4.3. An additional workaround to mitigate this problem without patching the redis-server executable is to block access to prevent unauthenticated users from connecting to Redis. This can be done in different ways. Either using network access control tools like firewalls, iptables, security groups, etc, or enabling TLS and requiring users to authenticate using client side certificates.
Cite this page
CVE-2025-21605. CVEDatabase.com. Retrieved 1 May 2026. https://cvedatabase.com/cve/CVE-2025-21605
Use CWE-770, Redis vendor hub and Redis product page to widen CVE-2025-21605 into its surrounding weakness, vendor, and product context.
Compare it with CVE-2025-49844, CVE-2025-62507 and CVE-2025-48367 for nearby disclosures in the same product family.