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The CVE-2021-33909 vulnerability, also known as “Sequoia,” is a use-after-free flaw in the Linux kernel’s sequence file system operation. The issue resides in the `fs/seq_file.c` component. When a user mounts a filesystem with a pathname exceeding the maximum allowed length (PAGE_SIZE), the `seq_file` interface mishandles memory. The `seq_buf_alloc()` function allocates a buffer for the pathname. If an error occurs during a subsequent filesystem operation, the `single_release()` function is called. This function frees the allocated buffer. However, if the operation is retried, the `seq_file` structure retains a dangling pointer to the now-freed buffer. A local attacker can exploit this by manipulating the memory allocator’s state to place controlled data in the freed memory location. When the kernel dereferences this dangling pointer, it leads to a use-after-free condition, potentially allowing for arbitrary code execution with kernel privileges.
Platform: Linux Kernel
Version: 3.16 to 5.13
Vulnerability : Use-After-Free
Severity: Critical
date: 2021-07-20
Prediction: 2021-07-27
What Undercode Say:
`gcc exploit.c -o exploit`
`./exploit`
`dmesg | grep seq_file`
`cat /proc/self/mountinfo | grep longpath`
`echo $?`
How Exploit:
Local privilege escalation via crafted long pathname.
Protection from this CVE:
Update kernel, Apply patch.
Impact:
Arbitrary code execution, Root access.
🎯Let’s Practice Exploiting & Learn Patching For Free:
Sources:
Reported By: nvd.nist.gov
Extra Source Hub:
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