CVE-2021-21309

What it is

Redis is an open-source, in-memory database that persists on disk. In affected versions of Redis an integer overflow bug in 32-bit Redis version 4.0 or newer could be exploited to corrupt the heap and potentially result with remote code execution. Redis 4.0 or newer uses a configurable limit for the maximum supported bulk input size. By default, it is 512MB which is a safe value for all platforms. If the limit is significantly increased, receiving a large request from a client may trigger several integer overflow scenarios, which would result with buffer overflow and heap corruption. We believe this could in certain conditions be exploited for remote code execution. By default, authenticated Redis users have access to all configuration parameters and can therefore use the “CONFIG SET proto-max-bulk-len” to change the safe default, making the system vulnerable. **This problem only affects 32-bit Redis (on a 32-bit system, or as a 32-bit executable running on a 64-bit system).** The problem is fixed in version 6.2, and the fix is back ported to 6.0.11 and 5.0.11. Make sure you use one of these versions if you are running 32-bit Redis. An additional workaround to mitigate the problem without patching the redis-server executable is to prevent clients from directly executing `CONFIG SET`: Using Redis 6.0 or newer, ACL configuration can be used to block the command. Using older versions, the `rename-command` configuration directive can be used to rename the command to a random string unknown to users, rendering it inaccessible. Please note that this workaround may have an additional impact on users or operational systems that expect `CONFIG SET` to behave in certain ways.

At a glance

Exploitability

Can be exploited over the network without logging in. Limited direct impact.

Exploit odds

4.8% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2021-02-26 22:15 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-06-17 03:35 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 4.8% in the next 30 days (EPSS).
• Severity: 5.4 MEDIUM (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2021-02-26 22:15 UTC

Last modified

2026-06-17 03:35 UTC

Exploit probability

4.8% · EPSS, next 30 days

Weakness

CWE-190 · Integer overflow

Record status

Modified

Affected

• Redislabs Redis < 5.0.11
• Redislabs Redis < 6.0.11

Attack profile CVSS 3.1 · 5.4

Attack vector

Network

Complexity

High

Privileges needed

None

User interaction

None

Scope

Changed

Confidentiality

None

Integrity

Low

Availability

Low

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2021-21309.md and follow it. Check whether this project is affected by CVE-2021-21309. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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