# CVE-2021-4439: linux: In the Linux kernel, the following vulnerability has been resolved:  isdn: cpai: check ctr->cnr to avoid array index...

CVE-2021-4439 is fixed in linux on 1 platform, first by DEBIAN-CVE-2021-4439, released June 20, 2024. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2021-4439
- Priority: High
- CVSS: 7.8 (high)
- EPSS: 0.0024
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jun 20, 2024

## 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]

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 5.14.16-1 | [DEBIAN-CVE-2021-4439](https://patchblox.com/security/data/fix/linux/debian-cve-2021-4439.md) | Jun 20, 2024 |
| Linux | linux Debian 13.5 (trixie) | 5.14.16-1 | [DEBIAN-CVE-2021-4439](https://patchblox.com/security/data/fix/linux/debian-cve-2021-4439.md) | Jun 20, 2024 |
| Linux | linux Debian 14 | 5.14.16-1 | [DEBIAN-CVE-2021-4439](https://patchblox.com/security/data/fix/linux/debian-cve-2021-4439.md) | Jun 20, 2024 |

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