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CVE-2021-33909

31
FAUCET Score

CVE-2021-33909, dubbed "Sequoia," is an integer overflow and out-of-bounds write vulnerability in the Linux kernel's fs/seq_file.c, affecting versions 3.16 through 5.13.x before 5.13.4. This flaw allows an unprivileged local user to escalate privileges to root, impacting various distributions including Debian, Fedora, and Oracle. With a CVSS score of 7.8 (High), it presents a significant risk due to its low attack complexity and potential for complete compromise of confidentiality, integrity, and availability. While there is no known active exploitation or public exploit code (Metasploit, Nuclei, ExploitDB), the vulnerability has garnered substantial community discussion and media coverage, indicating high awareness and potential for future exploitation.

Impacted Technologies

VendorProductVersion(s)CPE
>= 3.12.43, < 3.13CPE matchmatch criteria
cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
>= 3.16, < 4.4.276CPE matchmatch criteria
cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
>= 4.5, < 4.9.276CPE matchmatch criteria
cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
>= 4.10, < 4.14.240CPE matchmatch criteria
cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
>= 4.15, < 4.19.198CPE matchmatch criteria
cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*

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
9.73%
Probability of exploitation in next 30 days
EPSS Percentile
95.0%
Percentile rank of EPSS score among Peer Group
As of 2026-07-25
Model: v2026.06.15
This CVE's current EPSS score of 0.0973 is in the 99th percentile among its peer group of 16,994 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

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 (33)

boschpatch availablevia llm_extracted
View patch
github_advisorypatch availablevia nvd_reference
View patch
microsoftpatch availablevia msrc
Product: 16920-16823Fixed in: 5.10.78.1-1
microsoftpatch availablevia msrc
Product: cbl2 kernel 5.10.78.1-1 on CBL Mariner 2.0Fixed in: 5.10.78.1-1
microsoftpatch availablevia msrc
Product: 16919-16820Fixed in: -
microsoftpatch availablevia msrc
Product: cm1 kernel 5.10.60.1-1 on CBL Mariner 1.0Fixed in: -
mongodbpatch availablevia llm_extracted
View patch
oraclepatch availablevia nvd_reference
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 7.2 Advanced Update SupportFixed in: kernel-0:3.10.0-327.98.2.el7
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 7.3 Advanced Update SupportFixed in: kernel-0:3.10.0-514.90.2.el7
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 7.4 Advanced Update SupportFixed in: kernel-0:3.10.0-693.90.2.el7
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 7.4 Telco Extended Update SupportFixed in: kernel-0:3.10.0-693.90.2.el7
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 7.4 Update Services for SAP SolutionsFixed in: kernel-0:3.10.0-693.90.2.el7
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 7.6 Advanced Update Support(Disable again in 2026 - SPRHEL-7118)Fixed in: kernel-0:3.10.0-957.78.2.el7
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 7.6 Telco Extended Update SupportFixed in: kernel-0:3.10.0-957.78.2.el7
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 7.6 Update Services for SAP SolutionsFixed in: kernel-0:3.10.0-957.78.2.el7
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 7.6 Update Services for SAP SolutionsFixed in: kpatch-patch
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 7.7 Extended Update SupportFixed in: kernel-0:3.10.0-1062.52.2.el7
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 7.7 Extended Update SupportFixed in: kpatch-patch
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8Fixed in: kernel-rt-0:4.18.0-305.10.2.rt7.83.el8_4
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8Fixed in: kernel-0:4.18.0-305.10.2.el8_4
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8Fixed in: kpatch-patch
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8.1 Extended Update SupportFixed in: kernel-0:4.18.0-147.51.2.el8_1
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8.1 Extended Update SupportFixed in: kpatch-patch
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8.2 Extended Update SupportFixed in: kernel-rt-0:4.18.0-193.60.2.rt13.112.el8_2
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8.2 Extended Update SupportFixed in: kernel-0:4.18.0-193.60.2.el8_2
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8.2 Extended Update SupportFixed in: kpatch-patch
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Virtualization 4 for Red Hat Enterprise Linux 7Fixed in: redhat-virtualization-host-0:4.3.17-20210713.0.el7_9
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Virtualization 4 for Red Hat Enterprise Linux 8Fixed in: redhat-virtualization-host-0:4.4.7-20210715.1.el8_4
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 6 Extended Lifecycle SupportFixed in: kernel-0:2.6.32-754.41.2.el6
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 7Fixed in: kernel-0:3.10.0-1160.36.2.el7
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 7Fixed in: kernel-rt-0:3.10.0-1160.36.2.rt56.1179.el7
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 7Fixed in: kpatch-patch
View patch

Vendor Advisories (4)

boschllm-bosch-74b0a6b23b62a91bHIGH

Linux kernel vulnerabilities (CVE-2021-33909, CVE-2021-33910)

Sep 23, 2021
mongodbllm-mongodb-dbaab95a7510d246HIGH

Multiple Linux kernel vulnerabilities (CVE-2021-33909, CVE-2021-33910)

Sep 23, 2021
redhatCVE-2021-33909Important

kernel: size_t-to-int conversion vulnerability in the filesystem layer

Jul 20, 2021
microsoft2021-Jul/CVE-2021-33909Important

fs/seq_file.c in the Linux kernel 3.16 through 5.13.x before 5.13.4 does not properly restrict seq buffer allocations leading to an integer overflow an Out-of-bounds Write and escalation to root by an unprivileged user aka CID-8cae8cd89f05.

Jul 13, 2021

References

packetstormsecurity.com / files/163621/Sequoia-A-Deep-Root-In-Linuxs-Filesystem-Layer.html
ExploitThird Party AdvisoryVDB Entry
packetstormsecurity.com / files/163671/Kernel-Live-Patch-Security-Notice-LSN-0079-1.html
Third Party AdvisoryVDB Entry
packetstormsecurity.com / files/164155/Kernel-Live-Patch-Security-Notice-LSN-0081-1.html
Third Party AdvisoryVDB Entry
packetstormsecurity.com / files/165477/Kernel-Live-Patch-Security-Notice-LSN-0083-1.html
Third Party AdvisoryVDB Entry
cdn.kernel.org / pub/linux/kernel/v5.x/ChangeLog-5.13.4
Mailing ListPatchVendor Advisory
github.com / torvalds/linux/commit/8cae8cd89f05f6de223d63e6d15e31c8ba9cf53b
PatchThird Party Advisory
lists.debian.org / debian-lts-announce/2021/07/msg00014.html
Mailing ListThird Party Advisory
lists.debian.org / debian-lts-announce/2021/07/msg00015.html
Mailing ListThird Party Advisory
lists.debian.org / debian-lts-announce/2021/07/msg00016.html
Mailing ListThird Party Advisory
lists.fedoraproject.org / archives/list/package-announce%40lists.fedoraproject.org/message/Z4UHHIGISO3FVRF4CQNJS4IKA25ATSFU
psirt.global.sonicwall.com / vuln-detail/SNWLID-2022-0015
Third Party Advisory
security.netapp.com / advisory/ntap-20210819-0004
Third Party Advisory
debian.org / security/2021/dsa-4941
Third Party Advisory
openwall.com / lists/oss-security/2021/07/20/1
ExploitMailing ListThird Party Advisory
oracle.com / security-alerts/cpujan2022.html
PatchThird Party Advisory
openwall.com / lists/oss-security/2021/07/22/7
Mailing ListThird Party Advisory
openwall.com / lists/oss-security/2021/08/25/10
Mailing ListThird Party Advisory
openwall.com / lists/oss-security/2021/09/17/2
Mailing ListThird Party Advisory
openwall.com / lists/oss-security/2021/09/17/4
Mailing ListThird Party Advisory
openwall.com / lists/oss-security/2021/09/21/1
Mailing ListThird Party Advisory