# CVE-2021-20235: libzmq5: There's a flaw in the zeromq server in versions before 4.3.3 in src/decoder_allocators.hpp

CVE-2021-20235 is fixed in libzmq5 on 1 platform, first by libzmq5 4.2.5-1ubuntu0.2+esm2, released May 28, 2021. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2021-20235
- Priority: Routine
- CVSS: n/a (Medium)
- EPSS: 0.4386
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Apr 1, 2021

## Description

There's a flaw in the zeromq server in versions before 4.3.3 in src/decoder_allocators.hpp. The decoder static allocator could have its sized changed, but the buffer would remain the same as it is a static buffer. A remote, unauthenticated attacker who sends a crafted request to the zeromq server could trigger a buffer overflow WRITE of arbitrary data if CURVE/ZAP authentication is not enabled. The greatest impact of this flaw is to application availability, data integrity, and confidentiality.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | libzmq5 Ubuntu 18.04.6 LTS (bionic) | 4.2.5-1ubuntu0.2+esm2 | [libzmq5 4.2.5-1ubuntu0.2+esm2](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-libzmq5-4.2.5-1ubuntu0.2-esm2.md) | May 28, 2021 |
| Linux | libzmq5 Ubuntu 20.04 LTS (focal) | 4.3.2-2ubuntu1.20.04.1~esm2 | [libzmq5 4.3.2-2ubuntu1.20.04.1~esm2](https://patchblox.com/security/data/fix/linux/ubuntu-focal-libzmq5-4.3.2-2ubuntu1.20.04.1-esm2.md) | May 28, 2021 |

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