CVE-2021-41073

What it actually does

Use-after-free in loop_rw_iter triggered via IORING_OP_PROVIDE_BUFFERS allows a local process to free a kernel buffer and subsequently reuse the dangling reference for arbitrary read/write in kernel memory.

Why it matters to the business

Local attackers on affected Linux systems can obtain full root privileges, enabling them to read or modify any data, install persistent malware, or disrupt operations on the host.

How an attack unfolds

An attacker with a local account crafts an io_uring submission that calls IORING_OP_PROVIDE_BUFFERS to cause the kernel to free a buffer, then uses the resulting dangling pointer (observed via /proc/<pid>/maps) to overwrite kernel structures and escalate to root.

How to fix it

Upgrade the Linux kernel to the commit 16c8d2df7ec0eed31b7d3b61cb13206a7fb930cc or later; apply the vendor-supplied update for the running distribution and reboot.

How to confirm the fix worked

Verify the running kernel contains commit 16c8d2df7ec0eed31b7d3b61cb13206a7fb930cc (uname -r or git describe) and confirm io_uring PROVIDE_BUFFERS handling no longer frees the buffer while references remain.

Typical attack path

1. Obtain local shell on target system
2. Create io_uring ring and submit IORING_OP_PROVIDE_BUFFERS request to trigger buffer free
3. Map process memory via /proc/self/maps to locate and reuse the freed kernel buffer
4. Overwrite kernel credentials or function pointers to gain root privileges
5. Execute payload or maintain access

How to detect it

Review kernel audit logs and dmesg for io_uring related warnings or crashes around the time of suspected activity; inspect process memory maps and io_uring submissions from untrusted users for anomalous PROVIDE_BUFFERS usage.

What your security team should do

• Immediately update all systems running kernels 5.10 through 5.14.6 to the fixed commit
• Restrict untrusted local accounts and disable io_uring where not required via kernel config or seccomp
• Monitor for new kernel releases and schedule reboots within the change window