isdn: cpai: check ctr->cnr to avoid array index out of bound
Key facts
- Attack vector
- Local
- Privileges required
- Low
- User interaction
- None
- Attack complexity
- Low
- Impact type
- Code execution
- Confidentiality · integrity · availability
- High · High · High
- Fix status
- Partial Red Hat: 3 without a fix
Attack profile from CVSS 3.1 · NVD. Fix status from CNA and Red Hat. Impact type from CWE-129 and the CVSS impact.
Summary
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]
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- No
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| Linux | Linux | 2.6.12 and later | 4.4.290, 4.9.288, 4.14.253, 4.19.214, 5.4.156, 5.10.76, 5.14.15, 5.15 | Patch available | CNA |
- Linux VendorLinux Affected 2.6.12 and later Fixed in 4.4.290, 4.9.288, 4.14.253, 4.19.214, 5.4.156, 5.10.76, 5.14.15, 5.15 Patch available CNA
CPE configurations NVD · 6
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | before 4.4.290; 4.5 to before 4.9.288; 4.10 to before 4.14.253; 4.15 to before 4.19.214; 4.20 to before 5.4.156; 5.5 to before 5.10.76; 5.11 to before 5.14.15 | Vulnerable | Linux |
| cpe:2.3:o:linux:linux_kernel:5.15:rc1:*:*:*:*:*:* | 5.15 rc1 | Vulnerable | Linux |
| cpe:2.3:o:linux:linux_kernel:5.15:rc2:*:*:*:*:*:* | 5.15 rc2 | Vulnerable | Linux |
| cpe:2.3:o:linux:linux_kernel:5.15:rc3:*:*:*:*:*:* | 5.15 rc3 | Vulnerable | Linux |
| cpe:2.3:o:linux:linux_kernel:5.15:rc4:*:*:*:*:*:* | 5.15 rc4 | Vulnerable | Linux |
| cpe:2.3:o:linux:linux_kernel:5.15:rc5:*:*:*:*:*:* | 5.15 rc5 | Vulnerable | Linux |
- cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* Versions before 4.4.290; 4.5 to before 4.9.288; 4.10 to before 4.14.253; 4.15 to before 4.19.214; 4.20 to before 5.4.156; 5.5 to before 5.10.76; 5.11 to before 5.14.15 Vulnerable ·Linux
- cpe:2.3:o:linux:linux_kernel:5.15:rc1:*:*:*:*:*:* Versions 5.15 rc1 Vulnerable ·Linux
- cpe:2.3:o:linux:linux_kernel:5.15:rc2:*:*:*:*:*:* Versions 5.15 rc2 Vulnerable ·Linux
- cpe:2.3:o:linux:linux_kernel:5.15:rc3:*:*:*:*:*:* Versions 5.15 rc3 Vulnerable ·Linux
- cpe:2.3:o:linux:linux_kernel:5.15:rc4:*:*:*:*:*:* Versions 5.15 rc4 Vulnerable ·Linux
- cpe:2.3:o:linux:linux_kernel:5.15:rc5:*:*:*:*:*:* Versions 5.15 rc5 Vulnerable ·Linux
Remediation
- Fix · CNA Linux (Linux) Fixed in 4.4.290, 4.9.288, 4.14.253, 4.19.214, 5.4.156, 5.10.76, 5.14.15, 5.15
Vendor assessments
Red Hat
Red Hat rating: Low. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Red Hat Enterprise Linux 6 | Affected | No fix planned: Out of support scope |
| Red Hat Enterprise Linux 7 | Affected | No fix planned: Out of support scope |
| Red Hat Enterprise Linux 8 | Affected | No fix yet |
Not affected: 1 product
- Red Hat Enterprise Linux 9
Timeline
- 2026-10-02 Threatist record created from CVE-2021-4439
- 2026-10-03 Alias added: GHSA-gcrq-r544-wxfh
References
Patch 8
- https://git.kernel.org/stable/c/e8b8de17e164c9f1b7777f1c6f99d05539000036
- https://git.kernel.org/stable/c/24219a977bfe3d658687e45615c70998acdbac5a
- https://git.kernel.org/stable/c/9b6b2db77bc3121fe435f1d4b56e34de443bec75
- https://git.kernel.org/stable/c/7d91adc0ccb060ce564103315189466eb822cc6a
- https://git.kernel.org/stable/c/285e9210b1fab96a11c0be3ed5cea9dd48b6ac54
- https://git.kernel.org/stable/c/7f221ccbee4ec662e2292d490a43ce6c314c4594
- https://git.kernel.org/stable/c/cc20226e218a2375d50dd9ac14fb4121b43375ff
- https://git.kernel.org/stable/c/1f3e2e97c003f80c4b087092b225c8787ff91e4d
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Sources
- CVE-2021-4439 · CVE Program
- CVE-2021-4439 · NVD
- FIRST EPSS
- GHSA-gcrq-r544-wxfh · GitHub Advisory Database · CC BY 4.0
- CVE-2021-4439 · Red Hat security data · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences