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CVE-2021-33656

24
FAUCET Score

CVE-2021-33656 describes an out-of-bounds write vulnerability in the Linux kernel, specifically when handling font data via the ioctl PIO_FONT command. This flaw impacts various Linux distributions, including Debian and openEuler. With a CVSS score of 6.8 (Medium), it presents a high impact on confidentiality, integrity, and availability, requiring physical access for exploitation. Currently, there is no evidence of active exploitation, public exploit code (Metasploit, Nuclei, ExploitDB), or significant community discussion surrounding this vulnerability.

Impacted Technologies

VendorProductVersion(s)CPE
20.03CPE matchmatch criteria
cpe:2.3:o:openatom:openeuler:20.03:-:*:*:lts:*:*:*
20.03CPE matchmatch criteria
cpe:2.3:o:openatom:openeuler:20.03:sp1:*:*:lts:*:*:*
20.03CPE matchmatch criteria
cpe:2.3:o:openatom:openeuler:20.03:sp3:*:*:lts:*:*:*
< 5.10.127CPE matchmatch criteria
cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
10.0CPE matchmatch criteria
cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

6.8MEDIUM

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

Attack Vector
PHYSICAL
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
HIGH
Exploitability Score
0.9
Impact Score
5.9
CvssVersion
3.1

Exploit Intelligence

EPSS Score
0.57%
Probability of exploitation in next 30 days
EPSS Percentile
43.9%
Percentile rank of EPSS score among Peer Group
As of 2026-07-25
Model: v2026.06.15
This CVE's current EPSS score of 0.0057 is in the 82nd percentile among its peer group of 1,531 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.1 Reddit, 0.1 Bluesky, 0.0 Mastodon, and 0.1 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.2 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (7)

microsoftpatch availablevia msrc
Product: 18667-16820Fixed in: -
microsoftpatch availablevia msrc
Product: cm1 kernel 5.10.131.1-1 on CBL Mariner 1.0Fixed in: -
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8Fixed in: kernel-0:4.18.0-477.10.1.el8_8
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Virtualization 4 for Red Hat Enterprise Linux 8Fixed in: kernel-0:4.18.0-372.70.1.el8_6
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8.6 Extended Update SupportFixed in: kernel-0:4.18.0-372.70.1.el8_6
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8Fixed in: kernel-rt-0:4.18.0-477.10.1.rt7.274.el8_8
View patch
redhatno patchvia redhat_api
Product: Red Hat Enterprise Linux 9Fixed in: kernel

Vendor Advisories (2)

microsoft2022-Jul/CVE-2021-33656Moderate

When setting font with malicous data by ioctl cmd PIO_FONTkernel will write memory out of bounds.

Jul 12, 2022
redhatCVE-2021-33656Moderate

kernel: when setting font with malicious data by ioctl PIO_FONT, kernel will write memory out of bounds

Jan 5, 2021

References

git.kernel.org / pub/scm/linux/kernel/git/stable/stable-queue.git/tree/releases/5.10.127/vt-drop-old-font-ioctls.patch
PatchThird Party Advisory
lists.debian.org / debian-lts-announce/2022/10/msg00000.html
Mailing ListThird Party Advisory
openeuler.org / en/security/cve/detail.html
Third Party Advisory
openwall.com / lists/oss-security/2022/07/19/3
Mailing ListPatchThird Party Advisory