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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 specially crafted `ls -l` shell commands on directories with deep path structures. By creating a directory with a pathname exceeding 8MB, an unprivileged local user can trigger an integer overflow in the `fs/seq_file.c` code. This overflow leads to an under-allocation of a buffer. Subsequent operations on this malformed directory force the kernel to write beyond the bounds of the inadequately sized buffer, corrupting adjacent kernel memory. This corruption results in a use-after-free condition where the kernel attempts to access a memory object that has already been freed. A successful exploit can leverage this memory corruption to achieve arbitrary code execution with kernel privileges, effectively granting full control over 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:
`ls -la /tmp/$(python -c ‘print(“A”1000000)’)`
`mkdir -p $(python -c ‘print(“A”1000000)/’1000)`
`dmesg | grep -i “segfault\|oops\|general protection fault”`
How Exploit:
Local Privilege Escalation to root.
Protection from this CVE:
Update kernel to 5.13.4 or later. Apply vendor security patches. Restrict user namespaces if unused.
Impact:
Full system compromise, kernel crash, arbitrary code execution.
🎯Let’s Practice Exploiting & Learn Patching For Free:
Sources:
Reported By: nvd.nist.gov
Extra Source Hub:
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