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What is CVE-2025-21605?A high-severity flaw in Redis, explained.

High severity3 affected products
The short answer

CVE-2025-21605 is a high-severity flaw (CVSS 7.5) in Redis, published on 23 April 2025. It is not on the list of flaws known to be exploited today. The latest forecast puts its chance of use in the next 30 days at 0.9%. If you run an affected version, plan in the vendor’s fix.

Check if it affects you →How to fix it

Published 23 April 2025. Record last updated 5 September 2025. We keep this page's data up to date.

What it does

What is CVE-2025-21605? In plain terms.

It can be attacked from anywhere on the internet without logging in, and nobody has to click anything. If it works, the attacker can take it offline.

The official 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.

What kind of flaw is it?

  • CWE-770Allocation of Resources Without Limits or Throttling
CVSS 3.1 scoreHigh · 7.5

How an attack on it works

Read straight from its severity rating, translated out of the shorthand.

  • Where an attacker can beAnywhere on the internet
  • How hard it is to pull offEasy: no special conditions
  • Login needed firstNo login needed
  • Does someone have to clickNo, nobody has to do anything
  • What an attacker getsCan take it offline

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

Exploitation

Is CVE-2025-21605 being exploited? Not that we know of.

It is not on the list of flaws known to be exploited today. The latest forecast puts the chance of it being used in the next 30 days at 0.9%. That can change at any time, which is why we keep watching.

Known to be exploitedNoNot on the list of exploited flaws today
Chance of use in the next 30 days0.9%Its EPSS score, from the latest forecast

Timeline

  1. Published
  2. Record last updated
How Precursor Intelligence ranks it
47out of 100Medium

CVE-2025-21605 scores 47. Action: Plan remediation.

We keep the score of every published flaw up to date as the evidence changes. Four things go into the score, and evidence that criminals are actually using it counts most. In order:

  • Evidence it is being exploitedBiggest factor
  • How severe it isStrong factor
  • How widely exposed it isSmaller factor
  • Threat activity around itSmaller factor

85 and above is Critical. Anything confirmed as exploited is always marked for an emergency patch, whatever its score.

When CVE-2025-21605 matches software you track, it lands in your list with its score and the reasons behind it.

See your own ranked list →
Affected products

Who is affected by CVE-2025-21605? 3 products.

The published record lists 3 products from 3 vendors. Versions are shown as published: "2.6.0 to before 7.4.3" means from 2.6.0 up to, but not including, 7.4.3. If you run one of these, check your version, then go to the fix below.

  • Application

    Redis

    by Redis

    Affected versions
    2.6.0 to before 7.4.3
  • Application

    Valkey

    by Lfprojects

    Affected versions
    7.2.4 to before 7.2.98.0.0 to before 8.0.38.1.0 to before 8.1.1
  • Operating system

    Debian Linux

    by Debian

    Affected versions
    11.0
Remediation

How do I fix CVE-2025-21605? Four steps.

  1. Check whether you run itCompare your versions with the affected products above. Not sure what you run? Precursor Intelligence can work it out from your public website, or you can pick it from a list.
  2. Apply the vendor’s fixInstall the latest update from the vendor. The references list where the vendor has published details.
  3. If you can’t patch todayFollow any mitigation the vendor publishes, and limit who can reach the affected system from the internet until the update is in.
  4. Keep an eye on itTrack the product and we tell you as soon as we spot this flaw on the list of exploited flaws, or a jump in its exploit likelihood.

References

4 links
Precursor Intelligence

Does CVE-2025-21605 affect you? We'll keep checking.

Looking flaws up one at a time doesn't scale. Tell us what you run once, and we tell you which flaws matter to you, in what order, and keep watching for new ones.

  1. Tell us what you runPick your software from a list, or let us work it out from your website.
  2. We match it to every flawOver 400,000 published flaws, checked against your list.
  3. Ranked by real-world riskA 0 to 100 score, led by evidence criminals are using it.
  4. Told as soon as we knowAn alert by email, in the app or by webhook to your own tools.
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FAQ

Common questions, answered plainly.

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CVE-2025-21605 is a high-severity flaw in Redis, published on 23 April 2025. It can be attacked from anywhere on the internet without logging in, and nobody has to click anything. If it works, the attacker can take it offline.

It scores 7.5 out of 10 on the CVSS severity scale, which is high. Our risk score for CVE-2025-21605 is 47 out of 100, which is Medium. Its action is "Plan remediation". No sign of exploitation and a low forecast. Patch it in your normal update cycle.

It is not on the list of flaws known to be exploited today. The latest forecast puts the chance of it being used in the next 30 days at 0.9%. That can change at any time, which is why we keep watching.

For Redis: 2.6.0 to before 7.4.3. The record lists 3 products in all, each with its versions, under "Who is affected" on this page.

Install the update the vendor names in its advisory. If you can't patch today, follow the vendor's mitigation and limit who can reach the affected system from the internet.

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