CVE-2021-3527

Guest-triggered process crash via unbounded stack allocation

Published May 26, 2021 · Updated Aug 3, 2024

Resource exhaustion in QEMU usb-redir allows guest OS users to crash the host QEMU process through oversized combined USB transfers. The usbredir_handle_bulk_data() path uses the attacker-influenced combined transfer size for an unbounded variable-length array on the stack. Guest control of USB traffic through an attached usb-redir device is required, and excessive stack allocation terminates the affected virtual machine process.

CVSS severity5.5
Medium
EPSS probability0.37%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Resource exhaustion in QEMU usb-redir allows guest OS users to crash the host QEMU process through oversized combined USB transfers. The usbredir_handle_bulk_data() path uses the attacker-influenced combined transfer size for an unbounded variable-length array on the stack. Guest control of USB traffic through an attached usb-redir device is required, and excessive stack allocation terminates the affected virtual machine process.

The record

CVE
CVE-2021-3527
Published
May 26, 2021
Updated
Aug 3, 2024
Vendor
QEMU Project
Product
QEMU
Classifications
CWE-770, T1499.004
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. May 26, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

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  1. Affected versionversion=all versions

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

QEMU Project · QEMUversion=all versions

Published CVSS scores

2.1NIST NVDAV:L/AC:L/Au:N/C:N/I:N/A:P
5.5NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-770Allocation of Resources Without Limits or Throttling
T1499.004Endpoint Denial of Service: Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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