# CVE-2021-42387: clickhouse: Heap out-of-bounds read in Clickhouse's LZ4 compression codec when parsing a malicious query

CVE-2021-42387 is fixed in 5 products on 1 platform, first by clickhouse-client 18.16.1+ds-7ubuntu0.1, released March 14, 2022. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2021-42387
- Priority: High
- CVSS: 8.1 (high)
- EPSS: 0.0157
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Mar 14, 2022

## Description

Heap out-of-bounds read in Clickhouse's LZ4 compression codec when parsing a malicious query. As part of the LZ4::decompressImpl() loop, a 16-bit unsigned user-supplied value ('offset') is read from the compressed data. The offset is later used in the length of a copy operation, without checking the upper bounds of the source of the copy operation.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | clickhouse Debian 12.15 (bookworm) | 18.16.1+ds-7.3 | [DEBIAN-CVE-2021-42387](https://patchblox.com/security/data/fix/linux/debian-cve-2021-42387.md) | Mar 14, 2022 |
| Linux | clickhouse-client Ubuntu 20.04 LTS (focal) | 18.16.1+ds-7ubuntu0.1 | [clickhouse-client 18.16.1+ds-7ubuntu0.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-clickhouse-client-18.16.1-ds-7ubuntu0.1.md) | Mar 14, 2022 |
| Linux | clickhouse-common Ubuntu 20.04 LTS (focal) | 18.16.1+ds-7ubuntu0.1 | [clickhouse-common 18.16.1+ds-7ubuntu0.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-clickhouse-common-18.16.1-ds-7ubuntu0.1.md) | Mar 14, 2022 |
| Linux | clickhouse-server Ubuntu 20.04 LTS (focal) | 18.16.1+ds-7ubuntu0.1 | [clickhouse-server 18.16.1+ds-7ubuntu0.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-clickhouse-server-18.16.1-ds-7ubuntu0.1.md) | Mar 14, 2022 |
| Linux | clickhouse-tools Ubuntu 20.04 LTS (focal) | 18.16.1+ds-7ubuntu0.1 | [clickhouse-tools 18.16.1+ds-7ubuntu0.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-clickhouse-tools-18.16.1-ds-7ubuntu0.1.md) | Mar 14, 2022 |

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Data as of 2026-11-08T13:06:02Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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