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CVE-2021-38166

26
FAUCET Score

CVE-2021-38166 is an integer overflow and out-of-bounds write vulnerability in the Linux kernel's BPF hashtable implementation (kernel/bpf/hashtab.c), affecting versions through 5.13.8, including various Debian and Fedora distributions. Rated 7.8 HIGH, this local vulnerability (AV:L/AC:L/PR:L) allows an attacker with CAP_SYS_ADMIN privileges to achieve high confidentiality, integrity, and availability impacts. There is currently no evidence of active exploitation, public exploit code (Metasploit, Nuclei, ExploitDB), or significant community discussion or media coverage, suggesting it is not widely targeted.

Impacted Technologies

VendorProductVersion(s)CPE
<= 5.13.8CPE matchmatch criteria
cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
33CPE matchmatch criteria
cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:*
34CPE matchmatch criteria
cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:*
11.0CPE matchmatch criteria
cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

7.8HIGH

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

Attack Vector
LOCAL
Attack Complexity
LOW
Privileges Required
LOW
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
HIGH
Exploitability Score
1.8
Impact Score
5.9
CvssVersion
3.1

Exploit Intelligence

EPSS Score
0.32%
Probability of exploitation in next 30 days
EPSS Percentile
24.3%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0032 is in the 62nd percentile among its peer group of 17,070 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.1 Reddit, 0.2 Bluesky, 0.1 Mastodon, and 0.2 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.3 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (6)

microsoftpatch availablevia msrc
Product: 16919-16820Fixed in: -
microsoftpatch availablevia msrc
Product: 16920-16823Fixed in: 5.10.78.1-1
microsoftpatch availablevia msrc
Product: cm1 kernel 5.10.60.1-1 on CBL Mariner 1.0Fixed in: -
microsoftpatch availablevia msrc
Product: cbl2 kernel 5.10.78.1-1 on CBL Mariner 2.0Fixed in: 5.10.78.1-1
redhatno patchvia redhat_api
Product: Red Hat Enterprise Linux 8Fixed in: kernel
redhatno patchvia redhat_api
Product: Red Hat Enterprise Linux 8Fixed in: kernel-rt

Vendor Advisories (2)

microsoft2021-Aug/CVE-2021-38166Important

In kernel/bpf/hashtab.c in the Linux kernel through 5.13.8 there is an integer overflow and out-of-bounds write when many elements are placed in a single bucket. NOTE: exploitation might be impractical without the CAP_SYS_ADMIN capability.

Aug 10, 2021
redhatCVE-2021-38166Moderate

kernel: integer overflow and out-of-bounds write in kernel/bpf/hashtab.c when many elements are placed in a single bucket

Aug 7, 2021

References

git.kernel.org / pub/scm/linux/kernel/git/bpf/bpf.git/commit
PatchVendor Advisory
lists.fedoraproject.org / archives/list/package-announce%40lists.fedoraproject.org/message/GUVLBJKZMWA3E3YXSH4SZ7BOYGJP4GXP
lists.fedoraproject.org / archives/list/package-announce%40lists.fedoraproject.org/message/UL6CH5M5PRLMA3KPBX4LPUO6Z73GRISO
lore.kernel.org / bpf/20210806150419.109658-1-th.yasumatsu%40gmail.com
security.netapp.com / advisory/ntap-20210909-0001
Third Party Advisory
debian.org / security/2021/dsa-4978
Third Party Advisory