CVE-2021-4439 isdn: cpai: check ctr->cnr to avoid array index out of bound
A local attacker can trigger an out-of-bounds array access in the Linux kernel ISDN CAPI driver, causing a system crash.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2021-4439?
CVE-2021-4439 is a high-severity memory corruption vulnerability in Linux kernel, published on 20 Jun 2024. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
isdn: cpai: check ctr->cnr to avoid array index out of bound
The cmtp_add_connection() would add a cmtp session to a controller and run a kernel thread to process cmtp.
__module_get(THIS_MODULE); session->task = kthread_run(cmtp_session, session, "kcmtpd_ctr_%d", session->num);
During this process, the kernel thread would call detach_capi_ctr() to detach a register controller. if the controller was not attached yet, detach_capi_ctr() would trigger an array-index-out-bounds bug.
[ 46.866069][ T6479] UBSAN: array-index-out-of-bounds in drivers/isdn/capi/kcapi.c:483:21 [ 46.867196][ T6479] index -1 is out of range for type 'capi_ctr *[32]' [ 46.867982][ T6479] CPU: 1 PID: 6479 Comm: kcmtpd_ctr_0 Not tainted 5.15.0-rc2+ #8 [ 46.869002][ T6479] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-2 04/01/2014 [ 46.870107][ T6479] Call Trace: [ 46.870473][ T6479] dump_stack_lvl+0x57/0x7d [ 46.870974][ T6479] ubsan_epilogue+0x5/0x40 [ 46.871458][ T6479] __ubsan_handle_out_of_bounds.cold+0x43/0x48 [ 46.872135][ T6479] detach_capi_ctr+0x64/0xc0 [ 46.872639][ T6479] cmtp_session+0x5c8/0x5d0 [ 46.873131][ T6479] ? __init_waitqueue_head+0x60/0x60 [ 46.873712][ T6479] ? cmtp_add_msgpart+0x120/0x120 [ 46.874256][ T6479] kthread+0x147/0x170 [ 46.874709][ T6479] ? set_kthread_struct+0x40/0x40 [ 46.875248][ T6479] ret_from_fork+0x1f/0x30 [ 46.875773][ T6479]
Weakness: CWE-129
Which versions are affected by CVE-2021-4439?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2021-4439?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2021-4439 being exploited?
There is no known exploitation of CVE-2021-4439 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as DEBIAN-CVE-2021-4439, GHSA-gcrq-r544-wxfh, UBUNTU-CVE-2021-4439.