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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 exploiting a race condition during the reading of a directory, an attacker can trigger a scenario where the kernel attempts to access a virtual function in a `struct seq_operations` that has already been freed. This occurs because the kernel fails to properly manage the lifetime of the allocated object when a user-space process interrupts a file operation with a signal (SIGINT). The freed memory is then overwritten with a user-controlled payload, ultimately leading to a function pointer dereference and granting the attacker arbitrary code execution with kernel privileges, effectively bypassing all security restrictions on the 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 -l /proc/self/map_files/` & `kill -SIGINT $PID`
`userfaultfd` for heap Feng-Shui
`commit 0a5c49d7d792b867a7670a6b5e0d4c7a2c06a6e1`
How Exploit:
Race Condition
SIGINT Interruption
Heap Spraying
Protection from this CVE:
Update Kernel
Restrict user namespaces
Impact:
Local Privilege Escalation
Kernel Memory Corruption
Full System Compromise
🎯Let’s Practice Exploiting & Learn Patching For Free:
Sources:
Reported By: nvd.nist.gov
Extra Source Hub:
Undercode
