Guest-to-host code execution via cursor size overflow
Published Apr 29, 2022 · Updated Mar 21, 2025
Heap buffer overflow in QEMU qemu-kvm 7.0.0 allows privileged guest OS users to crash or execute code in the host process through QXL cursor data. The cursor_alloc function multiplies guest-controlled width and height in an int, underallocating the cursor buffer before qxl_unpack_chunks copies the full cursor data into it. Exploitation requires high privileges in a guest configured with a QXL video device and VNC graphics; a successful trigger crashes QEMU or runs code as its host process.
Summary
What happened
Heap buffer overflow in QEMU qemu-kvm 7.0.0 allows privileged guest OS users to crash or execute code in the host process through QXL cursor data. The cursor_alloc function multiplies guest-controlled width and height in an int, underallocating the cursor buffer before qxl_unpack_chunks copies the full cursor data into it. Exploitation requires high privileges in a guest configured with a QXL video device and VNC graphics; a successful trigger crashes QEMU or runs code as its host process.
The record
- CVE
- CVE-2021-4206
- Published
- Apr 29, 2022
- Updated
- Mar 21, 2025
- Vendor
- QEMU Project
- Product
- QEMU
- Classifications
- CWE-190, T1068
- Attack vector
- local
- Privileges
- admin
Timeline
How it unfolded
- Apr 29, 2022CVE publishedPublication date reported by the CVE source.
- Mar 21, 2025Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=qemu-kvm 7.0.0
What conditions does exploitation require?
What is affected?
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.
Weakness, pattern, technique
Public exploit references
- STAR Labs QXL cursor heap-overflow proof of conceptproof of concept · demonstrated
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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