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How the mentioned CVE works:
The CVE-2021-33909 vulnerability, also known as Sequoia, exists in the Linux kernel’s filesystem layer. The flaw is a use-after-free in the seq_file interface. A local attacker can trigger an integer overflow by creating a deeply nested directory structure with excessively long pathnames. When the `ls` command or similar list-directory utility traverses this structure, it triggers the integer overflow when calculating the buffer size for the `d_path()` function. This leads to an out-of-bounds write, corrupting kernel memory. By carefully controlling the heap layout, an attacker can exploit this memory corruption to execute arbitrary code with elevated kernel privileges, ultimately achieving a full system compromise from an unprivileged user account.
Platform: Linux Kernel
Version: 3.16 to 5.13.x
Vulnerability: Use-After-Free
Severity: Critical
date: 2021-07-20
Prediction: Patch Available
What Undercode Say:
`ls /tmp/exploit_tree`
`d_path() size calculation`
`kmalloc() heap spray`
`commit_fs_credentials()`
How Exploit:
Create nested directories.
Trigger integer overflow.
Control heap memory.
Execute arbitrary code.
Protection from this CVE
Update kernel version.
Apply security patch.
Restrict user namespaces.
Impact:
Local Privilege Escalation.
Full System Compromise.
Kernel Memory Corruption.
🎯Let’s Practice Exploiting & Learn Patching For Free:
Sources:
Reported By: nvd.nist.gov
Extra Source Hub:
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