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The CVE-2021-33909 vulnerability, also known as “Sequoia,” is a critical use-after-free flaw in the Linux kernel’s filesystem layer. It resides in the `seq_file` interface, which is used for producing output for files in the `/proc` directory. The vulnerability is triggered when an application performs specific operations that cause a sequence of `lseek()` and `read()` calls on a maliciously crafted filesystem image. A large offset passed to `lseek()` can lead to an integer overflow when calculating the buffer size for the seq_file->buf. This overflow results in an undersized buffer allocation. Subsequent `read()` operations write beyond the bounds of this buffer, corrupting adjacent kernel memory, including a `struct seq_operations` which contains function pointers. This memory corruption leads to a use-after-free condition, allowing a local, unprivileged attacker to gain arbitrary code execution within the kernel context, ultimately achieving root privileges on the vulnerable system.
Platform: Linux Kernel
Version: 3.16 to 5.13.x
Vulnerability: Use-After-Free
Severity: Critical
date: 2021-07-20
Prediction: 2021-07-27
What Undercode Say:
`$ cat /proc/self/maps`
`$ uname -r`
` apt update && apt upgrade`
How Exploit:
Craft malicious filesystem.
Trigger integer overflow.
Execute arbitrary code.
Protection from this CVE:
Update kernel version.
Restrict filesystem access.
Apply security patch.
Impact:
Local Privilege Escalation.
Full System Compromise.
Kernel Memory Corruption.
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Sources:
Reported By: nvd.nist.gov
Extra Source Hub:
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