CVE-2021-21309 Integer overflow on 32-bit systems
An integer overflow in 32-bit Redis allows remote code execution if the bulk input size limit is increased from its safe default.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2021-21309?
CVE-2021-21309 is a medium-severity vulnerability in redis, published on 26 Feb 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Weakness: CWE-190
Which versions are affected by CVE-2021-21309?
It affects 1 product.
Products include Redislabs Redis.
How do I fix CVE-2021-21309?
Upgrade to a fixed version.
Is CVE-2021-21309 being exploited?
There is no known exploitation of CVE-2021-21309 in the wild and no public exploit code.
Other vulnerabilities in redis
Sources
Also known as ALPINE-CVE-2021-21309, AZL-6843, CLEANSTART-2026-OV83989, DEBIAN-CVE-2021-21309, DLA-2576-1, GHSA-hgj8-vff2-7cjf and 4 more.