CVE-2021-47125: linux kernel — Fix

Description

In the Linux kernel, the following vulnerability has been resolved: sch_htb: fix refcount leak in htb_parent_to_leaf_offload The commit ae81feb7338c ("sch_htb: fix null pointer dereference on a null new_q") fixes a NULL pointer dereference bug, but it is not correct. Because htb_graft_helper properly handles the case when new_q is NULL, and after the previous patch by skipping this call which creates an inconsistency : dev_queue->qdisc will still point to the old qdisc, but cl->parent->leaf.q will point to the new one (which will be noop_qdisc, because new_q was NULL). The code is based on an assumption that these two pointers are the same, so it can lead to refcount leaks. The correct fix is to add a NULL pointer check to protect qdisc_refcount_inc inside htb_parent_to_leaf_offload.

Is your site exposed to CVE-2021-47125?

Run a free security scan — no signup, results in seconds.

CVSS v3.1 Score

5.5

MEDIUM

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected Products

Vendor	Product	Versions
linux	linux_kernel	5.12 — 5.12.10
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All

References

Advisories & Patches

https://git.kernel.org/stable/c/2411c02d03892a5057499f8102d0cc1e0f852416 https://git.kernel.org/stable/c/944d671d5faa0d78980a3da5c0f04960ef1ad893 https://git.kernel.org/stable/c/2411c02d03892a5057499f8102d0cc1e0f852416 https://git.kernel.org/stable/c/944d671d5faa0d78980a3da5c0f04960ef1ad893

Frequently Asked Questions

What is CVE-2021-47125? +

In the Linux kernel, the following vulnerability has been resolved: sch_htb: fix refcount leak in htb_parent_to_leaf_offload The commit ae81feb7338c ("sch_htb: fix null pointer dereference on a null new_q") fixes a NULL pointer dereference bug, but it is not correct. Because htb_graft_helper properly handles the case when new_q is NULL, and after the previous patch by skipping this call which creates an inconsistency : dev_queue->qdisc will still point to the old qdisc, but cl->parent->leaf.q will point to the new one (which will be noop_qdisc, because new_q was NULL). The code is based on an assumption that these two pointers are the same, so it can lead to refcount leaks. The correct fix is to add a NULL pointer check to protect qdisc_refcount_inc inside htb_parent_to_leaf_offload. It has a CVSS v3.1 base score of 5.5 (MEDIUM).

How severe is CVE-2021-47125? +

CVE-2021-47125 has a CVSS v3.1 score of 5.5 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance.

What products are affected by CVE-2021-47125? +

CVE-2021-47125 affects products from linux, specifically: linux_kernel. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2021-47125? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

Related Vulnerabilities

CVE-2025-9588 10.0

Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection') vulnerability in Iron Mountain Archiving Services Inc. …

CVE-2025-57870 10.0

A SQL Injection vulnerability exists in Esri ArcGIS Server versions 11.3, 11.4 and 11.5 on Windows, Linux and Kubernetes. This …

CVE-2026-48286 10.0

Adobe Campaign Classic (ACC) versions 7.4.3 build 9396 and earlier are affected by an Incorrect Authorization vulnerability that could result …

CVE-2026-13782 10.0

Use after free in Browser in Google Chrome prior to 150.0.7871.47 allowed a remote attacker who had compromised the renderer …

CVE-2026-48449 10.0

Adobe Campaign Classic (ACC) is affected by an Incorrect Authorization vulnerability that could result in arbitrary code execution in the …

CVE-2026-48303 10.0

Adobe Campaign Classic (ACC) versions 7.4.3 build 9394 and earlier are affected by an Incorrect Authorization vulnerability that could result …

CVE-2021-47125