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The CVE-2021-33909 vulnerability, also known as “Sequoia,” is a use-after-free flaw in the Linux kernel’s filesystem layer. The issue resides in the `seq_file` interface, which is used for producing files in the `/proc` filesystem. The vulnerability is triggered when a user writes a large size value (over INT_MAX) to the `/proc/
Platform: Linux Kernel
Version: 3.16 to 5.13
Vulnerability: Use-After-Free
Severity: Critical
date: 2021-07-20
Prediction: Patch available
What Undercode Say:
`cat /proc/self/mountinfo | wc -c`
`dmesg | grep -i “segfault”`
`gcc exploit.c -o exploit`
`./exploit`
How Exploit:
The exploit involves a local attacker triggering the integer overflow by writing a crafted large size to the vulnerable `seq_file` interface. This leads to a heap-based buffer overflow, which can be used to overwrite critical kernel structures. By carefully manipulating the kernel heap, an attacker can overwrite function pointers or other data to execute arbitrary code with kernel privileges.
Protection from this CVE:
Update the Linux kernel to version 5.13.4 or later. Apply security patches provided by your distribution vendor. Restrict access to system calls via seccomp filters. Use kernel hardening features like SLAB_FREELIST_HARDENED.
Impact:
Full system compromise. Privilege escalation from an unprivileged user to root. Complete bypass of security mechanisms (SELinux, AppArmor).
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Sources:
Reported By: nvd.nist.gov
Extra Source Hub:
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