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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` commands targeting directories with excessively long pathnames. When a user executes such a command, it triggers a race condition during the allocation of a buffer for the pathname. If the system is under memory pressure, the kernel may free this buffer but a subsequent operation fails to update the internal file pointer, leaving it referencing the now-freed memory. A local attacker can exploit this by repeatedly attempting to access the freed memory chunk after it has been reallocated and overwritten, ultimately leading to a crash or arbitrary code execution with elevated kernel privileges.
Platform: Linux Kernel
Version: 3.16 to 5.13.x
Vulnerability: Use-After-Free
Severity: Critical
date: 2021-07-20
Prediction: Patch 2021-07-20
What Undercode Say:
`ls -l /tmp/$(python3 -c ‘print(“A”1000000)’)`
`cat /sys/kernel/debug/kmemleak`
`dmesg | grep “segfault”`
How Exploit:
Craft long pathname.
Trigger race condition.
Execute arbitrary code.
Protection from this CVE
Update kernel version.
Restrict user access.
Disable unprivileged user namespaces.
Impact:
Local Privilege Escalation.
System Compromise.
Denial of Service.
🎯Let’s Practice Exploiting & Learn Patching For Free:
Sources:
Reported By: nvd.nist.gov
Extra Source Hub:
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