CVE-2025-21605 is a high-severity vulnerability affecting Redis, an open-source, in-memory database. The vulnerability exists in Redis versions starting from 2.6 and prior to 7.4.3, where an unauthenticated client can cause unlimited growth of output buffers. This can eventually lead to the server running out of memory or being terminated. The default Redis configuration does not limit the output buffer for normal clients, which allows this buffer to grow indefinitely over time.
In scenarios where password authentication is enabled but no password is provided, the client can still trigger the output buffer growth via "NOAUTH" responses, exacerbating the memory exhaustion issue. This vulnerability has been patched in version 7.4.3, and organizations are advised to upgrade to this version or implement mitigations.
Risk to organizations includes potential denial-of-service (DoS) situations where the Redis service becomes unavailable due to memory exhaustion. Given the high exploitability and the potential impact on business operations, organizations should prioritize patching immediately.
Mitigation strategies without immediate patching include restricting access to the Redis server, preventing unauthenticated users from connecting. This can be accomplished using network access control tools or enabling TLS with client-side certificate authentication.
Vulnerability Details
The CVSS score for CVE-2025-21605 is 7.5, indicating a high severity level. The vulnerability allows for denial of service due to exhaustion of memory resources, making it critical for organizations using affected versions of Redis to address this promptly.
The affected products include Redis, Valkey, and Debian Linux. The vulnerability was published on April 23, 2025, and its CWE classification is CWE-770, which refers to insufficient output buffer restrictions.
Technical Analysis
The root cause of this vulnerability lies in the lack of limitations on output buffers for unauthenticated clients. The attack vector is network-based, requiring low attack complexity, and no privileges are required for exploitation. User interaction is not necessary, which further simplifies the attack process.
This vulnerability impacts the availability of the Redis service, as an attacker may leverage it to cause significant disruption. The failure to limit output buffer sizes allows clients to send excessive data, consuming server resources and leading to a denial of service.
Risk & Impact Analysis
The real-world deployment risk of CVE-2025-21605 is significant. Organizations using Redis without adequate mitigations may face service interruptions, resulting in potential data loss or unavailability of critical applications relying on the database.
The urgency to address this vulnerability is high, given the CVSS score of 7.5 and its potential for exploitation. Organizations should assess their exposure and prioritize remediation steps accordingly.
Exploitation Status
Signal | Status |
|---|---|
Known Exploit | No |
Public PoC | No |
Actively Exploited | No |
Ransomware Use | No |
Affected Versions
The affected versions of Redis include those starting from 2.6 to prior to 7.4.3. Additionally, Valkey versions from 7.2.4 to prior to 7.2.9, and 8.0.0 to prior to 8.0.3 are also affected. For Debian Linux, the vulnerable version is 11.0.
Mitigation & Remediation
To mitigate this vulnerability, organizations should upgrade to Redis version 7.4.3 or later. If immediate patching is not feasible, consider employing network access control measures to restrict unauthenticated access to the Redis server. This can involve using firewalls, iptables, or enabling TLS with client-side certificate authentication.
For additional guidance on security best practices, organizations may consider reviewing our resources on penetration testing and continuous security assessments.
Detection Guidance
Organizations should monitor logs for anomalies indicative of unusual memory usage patterns in Redis. Look for spikes in memory consumption that exceed normal usage, and implement network signatures to detect unauthorized access attempts.
AppSecure Threat Intelligence Insight
CVE-2025-21605 highlights a critical gap in resource management within Redis that can lead to significant operational risks. As organizations increasingly rely on Redis for critical applications, understanding and addressing such vulnerabilities becomes paramount.
Security teams should stay informed about the latest vulnerabilities and trends in database security. Regular security assessments and adherence to best practices can help prevent exposure to similar vulnerabilities in the future.
For further insights into vulnerability management, organizations can benefit from exploring our vulnerability management program and the associated risks.
Additionally, organizations can learn about the importance of penetration testing methodology in identifying and addressing security weaknesses proactively.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
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