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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. When a user executes `ls -l` on a directory with a pathname exceeding 1GB, the `seq_file` interface allocates a buffer. However, if the resulting string output is larger than 2GB, an integer overflow occurs during the size calculation. This overflow leads to an undersized buffer allocation. Subsequent operations to fill this buffer cause a heap-based buffer overflow, corrupting adjacent kernel memory objects. This corruption can then be leveraged to trigger a use-after-free condition, where a program continues to use a pointer after the memory it points to has been freed, ultimately allowing a local, unprivileged user to achieve arbitrary code execution with elevated 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:
`ls -l /tmp/$(python3 -c ‘print(“A”1000000000)’)`
`dmesg | grep -i “segfault”`
`cat /sys/kernel/debug/seq_file_info`
How Exploit:
Craft long path.
Trigger integer overflow.
Execute arbitrary code.
Protection from this CVE
Update kernel version.
Restrict user access.
Apply security patch.
Impact:
Privilege Escalation
System Compromise
DoS Possible
🎯Let’s Practice Exploiting & Learn Patching For Free:
Sources:
Reported By: nvd.nist.gov
Extra Source Hub:
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