CVE-2025-21605: redis DoS (CVSS 7.5)

Description

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.

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CVSS v3.1 Score

7.5

HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Weakness Type (CWE)

CWE-770 CWE-770

Affected Products

Vendor	Product	Versions
redis	redis	2.6.0 — 6.2.18
redis	redis	7.0 — 7.2.8
redis	redis	7.4.0 — 7.4.3
lfprojects	valkey	7.2.4 — 7.2.9
lfprojects	valkey	8.0.0 — 8.0.3
lfprojects	valkey	8.1.0 — 8.1.1
debian	debian_linux	All

References

Other References

https://github.com/redis/redis/releases/tag/7.4.3 https://github.com/redis/redis/security/advisories/GHSA-r67f-p999-2gff https://github.com/valkey-io/valkey/releases/tag/8.1.1 https://lists.debian.org/debian-lts-announce/2025/05/msg00014.html https://www.vicarius.io/vsociety/posts/cve-2025-21605-detection-script-memory-exhaustion-vulnerability-in-redis-database https://www.vicarius.io/vsociety/posts/cve-2025-21605-mitigation-script-memory-exhaustion-vulnerability-in-redis-database

Frequently Asked Questions

What is CVE-2025-21605? +

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. It has a CVSS v3.1 base score of 7.5 (HIGH).

How severe is CVE-2025-21605? +

CVE-2025-21605 has a CVSS v3.1 score of 7.5 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching.

What products are affected by CVE-2025-21605? +

CVE-2025-21605 affects products from debian, lfprojects, redis, specifically: debian_linux, redis, valkey. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2025-21605? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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