CVE-2020-36789

Medium

In the Linux kernel, the following vulnerability has been resolved: can: dev: can_get_echo_skb(): prevent call to kfree_skb() in hard IRQ context If a driver calls can_get_echo_skb() during a hardware IRQ (which is often, but not always, the case), the 'WARN_ON(in_irq)' in net/core/skbuff.c#skb_release_head_state() might be triggered, under network congestion circumstances, together with the potential risk of a NULL pointer dereference. The root cause of this issue is the call to kfree_skb() instead of dev_kfree_skb_irq() in net/core/dev.c#enqueue_to_backlog(). This patch prevents the skb to be freed within the call to netif_rx() by incrementing its reference count with skb_get(). The skb is finally freed by one of the in-irq-context safe functions: dev_consume_skb_any() or dev_kfree_skb_any(). The "any" version is used because some drivers might call can_get_echo_skb() in a normal context. The reason for this issue to occur is that initially, in the core network stack, loopback skb were not supposed to be received in hardware IRQ context. The CAN stack is an exeption. This bug was previously reported back in 2017 in [1] but the proposed patch never got accepted. While [1] directly modifies net/core/dev.c, we try to propose here a smoother modification local to CAN network stack (the assumption behind is that only CAN devices are affected by this issue). [1] http://lore.kernel.org/r/[email protected]

Package Linux Kernel
Published 2025-04-17
Last modified 2025-10-01
CVSS version 3.1
Patch available
Yes

CVSS 3.1 score

5.5

out of 10
Medium
Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
None
Availability
High
Vector string
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Weakness type

CWE-476

CVE-2020-36789 is a NULL Pointer Dereference vulnerability

What is NULL Pointer Dereference?

The product dereferences a pointer that it expects to be valid but is NULL, typically causing a crash. Learn more on MITRE CWE

Affected versions

Linux kernel versions 2.6.31 and later are affected. Fixed in 4.4.244, 4.9.244, 4.14.207, 4.19.158, 5.4.78, 5.9.9, 5.10 and their respective stable series.

Affected from
≥ 2.6.31
Fixed in
✓ 4.4.244 4.4.x ✓ 4.9.244 4.9.x ✓ 4.14.207 4.14.x ✓ 4.19.158 4.19.x ✓ 5.4.78 5.4.x ✓ 5.9.9 5.9.x ✓ 5.10

References

The following references provide additional information about CVE-2020-36789 including vendor advisories, patch commits, exploit details, and third-party analysis. Links are sourced from the NIST NVD database.

7 patch commits total View all on NVD

Frequently asked questions

  • What is CVE-2020-36789?

    CVE-2020-36789 is a Medium severity Linux kernel vulnerability with a CVSS score of 5.5 out of 10 , classified as a NULL Pointer Dereference flaw (CWE-476) . It affects Linux kernel versions from 2.6.31 onward and has been patched in 4.4.244, 4.9.244, 4.14.207 and others. CVE-2020-36789 has not been confirmed as actively exploited and is not listed in the CISA KEV catalog.

  • What is the CVSS score for CVE-2020-36789?

    CVE-2020-36789 has a CVSS score of 5.5 out of 10, rated Medium severity (CVSS 3.1). The vector string is CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H .

  • Is there a patch available for CVE-2020-36789?

    Yes — CVE-2020-36789 has been patched. Fixed versions include 4.4.244, 4.9.244, 4.14.207 and others. If you are running Linux kernel 2.6.31 or later up to the fix versions, apply the relevant patch for your kernel branch.

  • Is CVE-2020-36789 actively exploited?

    No — CVE-2020-36789 has not been confirmed as actively exploited. It is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog.

  • What is NULL Pointer Dereference (CWE-476)?

    The product dereferences a pointer that it expects to be valid but is NULL, typically causing a crash. View CWE-476 on MITRE CWE →

Back to
All CVEs
View on
NVD / NIST