Overview
This report examines the critical vulnerability, CVE-2025-21605, which affects Redis, an open-source in-memory database. By exploiting this vulnerability, an unauthenticated client can trigger unlimited growth of output buffers, causing the server to exhaust memory or be killed. This vulnerability presents a significant risk to any organization using affected Redis versions, as it could potentially lead to system compromise or data leakage.
Vulnerability Summary
CVE ID: CVE-2025-21605
Severity: High, CVSS score 7.5
Attack Vector: Network
Privileges Required: None
User Interaction: None
Impact: Potential system compromise or data leakage
Affected Products
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Product | Affected Versions
Redis | 2.6 to 7.4.2
How the Exploit Works
The exploit takes advantage of the default Redis configuration that does not limit the output buffer of normal clients. An unauthenticated client can connect to the Redis server and cause unlimited growth of output buffers, even without providing a password. The output buffer grows from “NOAUTH” responses until the system runs out of memory. This eventually leads to service exhaustion and unavailability of memory.
Conceptual Example Code
The following pseudo command represents how the vulnerability might be exploited:
redis-cli -h target.example.com append NOAUTH "[large string of characters]"In this example, an attacker continually appends a large string of characters to the ‘NOAUTH’ command, causing the output buffer to grow indefinitely.
Mitigation
The issue has been patched in Redis version 7.4.3. Users are urged to update to the patched version as soon as possible. If immediate patching is not feasible, users are advised to implement network access control tools such as firewalls, iptables, or security groups to block unauthenticated users from connecting to Redis. Alternatively, enabling TLS and requiring users to authenticate using client-side certificates can also help mitigate this vulnerability. As a temporary measure, a Web Application Firewall (WAF) or an Intrusion Detection System (IDS) can be used to detect and prevent potential exploitation attempts.
