CVE-2021-20255Public exploit

Guest-triggered host crash via recursive DMA reentry

Published Mar 9, 2021 · Updated Aug 3, 2024

Stack overflow in QEMU's eepro100 i8255x device emulator allows guest OS users to crash the host QEMU process through controller commands. The command unit follows guest-controlled DMA addresses back into its own MMIO command register, recursively reentering action_command until the host stack is exhausted. Exploitation requires a guest with access to a configured eepro100 device and results in CPU consumption or termination of that guest's QEMU process.

CVSS severity5.5
Medium
EPSS probability0.41%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stack overflow in QEMU's eepro100 i8255x device emulator allows guest OS users to crash the host QEMU process through controller commands. The command unit follows guest-controlled DMA addresses back into its own MMIO command register, recursively reentering action_command until the host stack is exhausted. Exploitation requires a guest with access to a configured eepro100 device and results in CPU consumption or termination of that guest's QEMU process.

The record

CVE
CVE-2021-20255
Published
Mar 9, 2021
Updated
Aug 3, 2024
Vendor
QEMU Project
Product
QEMU
Classifications
CWE-674, CWE-835, T1499.004
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Mar 9, 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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-674Uncontrolled Recursion
CWE-835Loop with Unreachable Exit Condition ('Infinite Loop')
T1499.004Application or System Exploitation

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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