What is CVE-2021-3409?

CVE-2021-3409 is a medium-severity vulnerability in Qemu, classified under Improper Restriction of Operations within the Bounds of a Memory Buffer. CVSS score: 5.7/10. Published 2021-03-23.

How severe is CVE-2021-3409?

Medium severity. CVSS v3 base score is 5.7 out of 10.

Is CVE-2021-3409 known to be exploited?

1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

Buffer overflow in Qemu

CVE-2021-3409

The patch for CVE-2020-17380/CVE-2020-25085 was found to be ineffective, thus making QEMU vulnerable to the out-of-bounds read/write access issues previously found in the SDHCI controller emulation code. This flaw allows a malicious privileged guest to crash the QEMU process on the host, resulting in a denial of service or potential code execution. QEMU up to (including) 5.2.0 is affected by this.

Vulnerability class: Buffer Overflow

Published 2021-03-23 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 5.7 (Medium). Vector: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:L/I:L/A:L.

EPSS exploit prediction

EPSS: 0.005 (39.7th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 40th percentile — 39.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.005 · newest: 0.005 · change: 0.000

Affected products

Qemu
Debian Linux — versions 9.0
Fedoraproject Fedora — versions 33
Red Hat Enterprise Linux — versions 7.0
Qemu — versions up to (including) 5.2.0

Weakness classification (CWE)

CWE-119 — Improper Restriction of Operations within the Bounds of a Memory Buffer

Public proof-of-concept exploits

sereok3/buffer-overflow-writeups

References

bugzilla.redhat.com/show_bug.cgi (Patch, Third Party Advisory, Issue Tracking)
www.openwall.com/lists/oss-security/2021/03/09/1 (Patch, Mailing List, Third Party Advisory)
lists.debian.org/debian-lts-announce/2021/04/msg00009.html (mailing-list, Third Party Advisory)
security.netapp.com/advisory/ntap-20210507-0001/ (Third Party Advisory)
security.gentoo.org/glsa/202208-27 (vendor-advisory, Third Party Advisory)

Frequently asked questions

What is CVE-2021-3409?: CVE-2021-3409 is a medium-severity vulnerability in Qemu, classified under Improper Restriction of Operations within the Bounds of a Memory Buffer. CVSS score: 5.7/10. Published 2021-03-23.
How severe is CVE-2021-3409?: Medium severity. CVSS v3 base score is 5.7 out of 10.
Is CVE-2021-3409 known to be exploited?: 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.