What is CVE-2021-3527?

CVE-2021-3527 is a medium-severity vulnerability in Qemu, classified under Allocation of Resources Without Limits or Throttling. CVSS score: 5.5/10. Published 2021-05-26.

How severe is CVE-2021-3527?

Medium severity. CVSS v3 base score is 5.5 out of 10.

Resource exhaustion in Qemu

CVE-2021-3527

A flaw was found in the USB redirector device (usb-redir) of QEMU. Small USB packets are combined into a single, large transfer request, to reduce the overhead and improve performance. The combined size of the bulk transfer is used to dynamically allocate a variable length array (VLA) on the stack without proper validation. Since the total size is not bounded, a malicious guest could use this flaw to influence the array length and cause the QEMU process to perform an excessive allocation on the stack, resulting in a denial of service.

Published 2021-05-26 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 5.5 (Medium). Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.004 (28.8th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 29th percentile — 28.8% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · change: 0.000

Affected products

Qemu
Debian Linux — versions 9.0, 10.0
Red Hat Enterprise Linux — versions 8.0
Qemu — versions all versions

Weakness classification (CWE)

CWE-770 — Allocation of Resources Without Limits or Throttling

References

bugzilla.redhat.com/show_bug.cgi (Patch, Third Party Advisory, Issue Tracking)
www.openwall.com/lists/oss-security/2021/05/05/5 (Patch, Mailing List, Third Party Advisory)
gitlab.com/qemu-project/qemu/-/commit/7ec54f9eb62b5d177e30eb8b1cad795a5f8d8986 (Patch, Third Party Advisory)
gitlab.com/qemu-project/qemu/-/commit/05a40b172e4d691371534828078be47e7fff524c (Patch, Third Party Advisory)
security.netapp.com/advisory/ntap-20210708-0008/ (Third Party Advisory)
lists.debian.org/debian-lts-announce/2021/09/msg00000.html (mailing-list, Mailing List, Third Party Advisory)
security.gentoo.org/glsa/202208-27 (vendor-advisory, Third Party Advisory)
lists.debian.org/debian-lts-announce/2022/09/msg00008.html (mailing-list, Mailing List, Third Party Advisory)

Frequently asked questions

What is CVE-2021-3527?: CVE-2021-3527 is a medium-severity vulnerability in Qemu, classified under Allocation of Resources Without Limits or Throttling. CVSS score: 5.5/10. Published 2021-05-26.
How severe is CVE-2021-3527?: Medium severity. CVSS v3 base score is 5.5 out of 10.