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NVD / CVE Program· CNA redhat

CVE-2021-3507: A heap buffer overflow was found in the floppy disk emulator of QEMU up to 6.0.0 (including).

Noroxi assessment

Priority: Monitor (action score 24/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.48% (FIRST EPSS).
  • Someone with local access to the system can trigger it. A low-privileged account is enough. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: qemu-guest-agent (AlmaLinux:9) 17:7.0.0-13.el9; qemu-img (AlmaLinux:9) 17:7.0.0-13.el9; qemu-kvm (AlmaLinux:9) 17:7.0.0-13.el9.

Low priority for now. Upgrade to qemu-guest-agent (AlmaLinux:9) 17:7.0.0-13.el9; qemu-img (AlmaLinux:9) 17:7.0.0-13.el9; qemu-kvm (AlmaLinux:9) 17:7.0.0-13.el9 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

A heap buffer overflow was found in the floppy disk emulator of QEMU up to 6.0.0 (including). It could occur in fdctrl_transfer_handler() in hw/block/fdc.c while processing DMA read data transfers from the floppy drive to the guest system. A privileged guest user could use this flaw to crash the QEMU process on the host resulting in DoS scenario, or potential information leakage from the host memory.

MediumCVSS 6.1 · v3.1—No exploit Fix available
Published
May 6, 2021
Updated
Jun 17, 2026
EPSS
0.4% · 42th percentile

Report tools

JSON

Action score

24

Monitor

Low priority for now.

CVSS
24 / 40 · 6.1 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.4%

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  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

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Noroxi analysis

What does it mean in your environment?

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
qemuqemu
debiandebian linux
redhatenterprise linux

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • debian debian linux10.0
  • qemu qemuup to 6.0.0 inclusive
  • redhat enterprise linux8.0

Versions reported by the vendor

Affected version ranges reported by the assigning authority (redhat). Independent of NVD's CPE analysis and usually ahead of it.

  • n/a QEMU

    • up to 6.0.0 (including)affected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
AlmaLinux:9qemu-guest-agentbefore 17:7.0.0-13.el917:7.0.0-13.el9
AlmaLinux:9qemu-imgbefore 17:7.0.0-13.el917:7.0.0-13.el9
AlmaLinux:9qemu-kvmbefore 17:7.0.0-13.el917:7.0.0-13.el9
AlmaLinux:9qemu-kvm-audio-pabefore 17:7.0.0-13.el917:7.0.0-13.el9
AlmaLinux:9qemu-kvm-block-curlbefore 17:7.0.0-13.el917:7.0.0-13.el9
AlmaLinux:9qemu-kvm-block-rbdbefore 17:7.0.0-13.el917:7.0.0-13.el9
AlmaLinux:9qemu-kvm-commonbefore 17:7.0.0-13.el917:7.0.0-13.el9
AlmaLinux:9qemu-kvm-corebefore 17:7.0.0-13.el917:7.0.0-13.el9
AlmaLinux:9qemu-kvm-device-display-virtio-gpubefore 17:7.0.0-13.el917:7.0.0-13.el9
AlmaLinux:9qemu-kvm-device-display-virtio-gpu-ccwbefore 17:7.0.0-13.el917:7.0.0-13.el9
AlmaLinux:9qemu-kvm-device-display-virtio-gpu-glbefore 17:7.0.0-13.el917:7.0.0-13.el9
AlmaLinux:9qemu-kvm-device-display-virtio-gpu-pcibefore 17:7.0.0-13.el917:7.0.0-13.el9
AlmaLinux:9qemu-kvm-device-display-virtio-gpu-pci-glbefore 17:7.0.0-13.el917:7.0.0-13.el9
AlmaLinux:9qemu-kvm-device-display-virtio-vgabefore 17:7.0.0-13.el917:7.0.0-13.el9
AlmaLinux:9qemu-kvm-device-display-virtio-vga-glbefore 17:7.0.0-13.el917:7.0.0-13.el9
AlmaLinux:9qemu-kvm-device-usb-hostbefore 17:7.0.0-13.el917:7.0.0-13.el9
AlmaLinux:9qemu-kvm-device-usb-redirectbefore 17:7.0.0-13.el917:7.0.0-13.el9
AlmaLinux:9qemu-kvm-docsbefore 17:7.0.0-13.el917:7.0.0-13.el9
AlmaLinux:9qemu-kvm-toolsbefore 17:7.0.0-13.el917:7.0.0-13.el9
AlmaLinux:9qemu-kvm-ui-egl-headlessbefore 17:7.0.0-13.el917:7.0.0-13.el9
AlmaLinux:9qemu-kvm-ui-openglbefore 17:7.0.0-13.el917:7.0.0-13.el9
AlmaLinux:9qemu-pr-helperbefore 17:7.0.0-13.el917:7.0.0-13.el9
Alpine:v3.16qemubefore 6.1.0-r06.1.0-r0
Debian:12qemubefore 1:7.1+dfsg-11:7.1+dfsg-1

+96

Same product

qemu: all records

Other highest-scoring records for the same primary product.

  • CVE-2019-12928The QMP migrate command in QEMU version 4.0.0 and earlier is vulnerable to OS command injection, which allows the remote attacker to…
    60This week
  • CVE-2015-8556Local privilege escalation vulnerability in the Gentoo QEMU package before 2.5.0-r1.
    44Plan
  • CVE-2017-15118A stack-based buffer overflow vulnerability was found in NBD server implementation in qemu before 2.11 allowing a client to request an…
    43Plan

Published before and after this one in the same product

  • ← EarlierCVE-2021-3392Mar 23, 2021 · A use-after-free flaw was found in the MegaRAID emulator of QEMU.
    12Monitor
  • ← EarlierCVE-2021-3409Mar 23, 2021 · 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…
    22Monitor
  • Later →CVE-2021-20181May 13, 2021 · A race condition flaw was found in the 9pfs server implementation of QEMU up to and including 5.2.0.
    30Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
almalinux:qemu-guest-agent17:7.0.0-13.el9 · AlmaLinux:9Package registry (OSV)
almalinux:qemu-img17:7.0.0-13.el9 · AlmaLinux:9Package registry (OSV)
almalinux:qemu-kvm17:7.0.0-13.el9 · AlmaLinux:9Package registry (OSV)
almalinux:qemu-kvm-audio-pa17:7.0.0-13.el9 · AlmaLinux:9Package registry (OSV)
almalinux:qemu-kvm-block-curl17:7.0.0-13.el9 · AlmaLinux:9Package registry (OSV)
almalinux:qemu-kvm-block-rbd17:7.0.0-13.el9 · AlmaLinux:9Package registry (OSV)
almalinux:qemu-kvm-common17:7.0.0-13.el9 · AlmaLinux:9Package registry (OSV)
almalinux:qemu-kvm-core17:7.0.0-13.el9 · AlmaLinux:9Package registry (OSV)
almalinux:qemu-kvm-device-display-virtio-gpu17:7.0.0-13.el9 · AlmaLinux:9Package registry (OSV)
almalinux:qemu-kvm-device-display-virtio-gpu-ccw17:7.0.0-13.el9 · AlmaLinux:9Package registry (OSV)
almalinux:qemu-kvm-device-display-virtio-gpu-gl17:7.0.0-13.el9 · AlmaLinux:9Package registry (OSV)
almalinux:qemu-kvm-device-display-virtio-gpu-pci17:7.0.0-13.el9 · AlmaLinux:9Package registry (OSV)
alpine:qemu6.1.0-r0 · Alpine:v3.16Package registry (OSV)
debian:qemu1:7.1+dfsg-1 · Debian:12Package registry (OSV)
opensuse:qemu3.1.1.1-150100.80.43.2 · openSUSE:Leap 15.3Package registry (OSV)
opensuse:qemu-linux-user6.2.0-150400.37.14.1 · openSUSE:Leap 15.4Package registry (OSV)
opensuse:qemu-testsuite6.2.0-150400.37.14.1 · openSUSE:Leap 15.4Package registry (OSV)
red hat:hivex0:1.3.18-23.module+el8.7.0+16689+53d59bc2 · Red Hat:enterprise_linux:8::appstreamPackage registry (OSV)
red hat:hivex-debuginfo0:1.3.18-23.module+el8.7.0+16689+53d59bc2 · Red Hat:enterprise_linux:8::appstreamPackage registry (OSV)
red hat:hivex-debugsource0:1.3.18-23.module+el8.7.0+16689+53d59bc2 · Red Hat:enterprise_linux:8::appstreamPackage registry (OSV)
red hat:hivex-devel0:1.3.18-23.module+el8.7.0+16689+53d59bc2 · Red Hat:enterprise_linux:8::appstreamPackage registry (OSV)
red hat:libguestfs1:1.44.0-9.module+el8.7.0+16689+53d59bc2 · Red Hat:enterprise_linux:8::appstreamPackage registry (OSV)
red hat:libguestfs-appliance1:1.44.0-9.module+el8.7.0+16689+53d59bc2 · Red Hat:enterprise_linux:8::appstreamPackage registry (OSV)
red hat:libguestfs-bash-completion1:1.44.0-9.module+el8.7.0+16689+53d59bc2 · Red Hat:enterprise_linux:8::appstreamPackage registry (OSV)
red hat:libguestfs-debuginfo1:1.44.0-9.module+el8.7.0+16689+53d59bc2 · Red Hat:enterprise_linux:8::appstreamPackage registry (OSV)
red hat:libguestfs-debugsource1:1.44.0-9.module+el8.7.0+16689+53d59bc2 · Red Hat:enterprise_linux:8::appstreamPackage registry (OSV)
red hat:libguestfs-devel1:1.44.0-9.module+el8.7.0+16689+53d59bc2 · Red Hat:enterprise_linux:8::appstreamPackage registry (OSV)
red hat:libguestfs-gfs21:1.44.0-9.module+el8.7.0+16689+53d59bc2 · Red Hat:enterprise_linux:8::appstreamPackage registry (OSV)
red hat:SLOF0:20210217-1.module+el8.7.0+16689+53d59bc2 · Red Hat:enterprise_linux:8::appstreamPackage registry (OSV)
rocky linux:hivex0:1.3.18-23.module+el8.7.0+1084+97b81f61 · Rocky Linux:8Package registry (OSV)

+12

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Someone with local access to the system can trigger it.
  • A low-privileged account is enough.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
high · data can be read
Integrity
none
Availability
low · the service can be disrupted
Attack vector
Local
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality impact
High
Integrity impact
None
Availability impact
Low

Weakness class (CWE)

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

CVSS vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:L

nvd-primary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

ATT&CK techniques

—

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (1 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records