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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’s handling of excessively long sequences. When an application uses the `seq_file` interface to output a large amount of data from the kernel, a single `write` operation to a file in `/proc` or `sysfs` is handled by the `seq_read_iter` function. If the total size of the sequence buffer exceeds the maximum allowed limit for a single `kmalloc()` call, the function fails to properly reallocate the buffer. This failure leads to an incorrect internal state where the buffer pointer is freed but a reference to it is retained. A subsequent read operation then uses this freed memory, corrupting kernel memory and allowing a local, unprivileged attacker to escalate privileges to root.
Platform: Linux Kernel
Version: 3.16-5.13.x
Vulnerability: Use-After-Free
Severity: Critical
date: 2021-07-20
Prediction: 2021-07-27
What Undercode Say:
`cat /proc/self/mountinfo`
`dmesg | grep “seq_file”`
`echo -e “include
`gcc exploit.c -o exploit`
How Exploit:
Local Privilege Escalation to root via memory corruption.
Protection from this CVE:
Update kernel, Apply patch.
Impact:
Full system compromise, Root access.
🎯Let’s Practice Exploiting & Learn Patching For Free:
Sources:
Reported By: nvd.nist.gov
Extra Source Hub:
Undercode
