What’s Vulnerable › Vulnerabilities

CVE-2021-33909

• Severity: high (CVSS 7.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 9.7% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2021-07-20 · updated 2026-06-17
• Weakness: CWE-190

Description

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.

Affected products

• Debian Linux: 9.0, 10.0
• Fedoraproject Fedora: 34
• Linux kernel: from 3.12.43 before 3.13; from 3.16 before 4.4.276; from 4.5 before 4.9.276; from 4.10 before 4.14.240; from 4.15 before 4.19.198; from 4.20 before 5.4.134 — fixed in 3.13, 4.14.240, 4.19.198, 4.4.276, 4.9.276, 5.10.52
• NetApp Hci Management Node: all versions
• NetApp Solidfire: all versions
• Oracle Corporation Communications Session Border Controller: 8.2, 8.3, 8.4, 9.0
• SonicWall SMA1000: through 12.4.2-02044

How to fix

Upgrade to a fixed version: Linux kernel 3.13, 4.14.240, 4.19.198, 4.4.276. Check the vendor advisory for mitigations.

References

• http://packetstormsecurity.com/files/163621/Sequoia-A-Deep-Root-In-Linuxs-Filesystem-Layer.html
• http://packetstormsecurity.com/files/163671/Kernel-Live-Patch-Security-Notice-LSN-0079-1.html
• http://packetstormsecurity.com/files/164155/Kernel-Live-Patch-Security-Notice-LSN-0081-1.html
• http://packetstormsecurity.com/files/165477/Kernel-Live-Patch-Security-Notice-LSN-0083-1.html
• http://www.openwall.com/lists/oss-security/2021/07/22/7
• http://www.openwall.com/lists/oss-security/2021/08/25/10
• http://www.openwall.com/lists/oss-security/2021/09/17/2
• http://www.openwall.com/lists/oss-security/2021/09/17/4
• http://www.openwall.com/lists/oss-security/2021/09/21/1
• https://cdn.kernel.org/pub/linux/kernel/v5.x/ChangeLog-5.13.4
• https://github.com/torvalds/linux/commit/8cae8cd89f05f6de223d63e6d15e31c8ba9cf53b
• https://lists.debian.org/debian-lts-announce/2021/07/msg00014.html

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