high CVSS 7.8 EPSS <0.1%

CVE-2021-47361·Kernel vulnerability

In the Linux kernel, the following vulnerability has been resolved: mcb: fix error handling in mcb_alloc_bus() There are two bugs: 1) If ida_simple_get() fails then this code calls put_device(carrier) but we haven't yet called get_device(carrier) and probably that leads to a use after free. 2) After device_initialize() then we need to use put_device() to release the bus. This will free the internal resources tied to the device and call mcb_free_bus() which will free the rest.

Severity
high
Software
Kernel
Fixed in
5.14.9
Published

How likely is exploitation

FIRST's Exploit Prediction Scoring System puts the probability of this CVE being exploited in the next 30 days at <0.1% — higher than 3% of all published CVEs. EPSS is an independent forecast of exploitation, not a severity rating: it says nothing about how much damage a successful attack does, which is what a CVSS score measures.

Read the two together. CVE-2021-47361 scores 7.8 on CVSS, so a successful attack would be serious — but at <0.1%, almost nobody is currently attempting it. That is a different situation from a flaw under mass exploitation, and it is usually the difference between patching on your next maintenance window and patching tonight.

Affected versions

From: 5.11

Until: 5.14.9

Fixed in: 5.14.9

How to fix this CVE

Update your Linux kernel to version 5.14.9 or later to resolve memory management issues in the MCB (MEN Chameleon Bus) subsystem that could lead to use-after-free conditions. Systems running kernel versions 5.11 through 5.14.8 should prioritize this patch to prevent potential privilege escalation from local users.

sudo dnf update kernel kernel-devel

Defensia detects this vulnerability

How to check if you are affected

  1. Step 1: Check your current kernel version with `uname -r` and compare against the affected range (5.11 to 5.14.8)
  2. Step 2: Verify MCB driver is loaded by running `lsmod | grep mcb` — if output appears, the component is present
  3. Step 3: Search system logs for MCB-related errors using `sudo journalctl -u kernel --grep='mcb\|ida_simple_get' | head -50`
  4. Step 4: After patching, reboot and confirm new kernel version with `uname -r`, then verify MCB module loads without errors using `sudo modprobe mcb` followed by `dmesg | tail -20`

FAQ

What is CVE-2021-47361?

This vulnerability involves two critical bugs in the MCB (MEN Chameleon Bus) kernel subsystem: improper reference counting when device allocation fails, and incorrect device cleanup procedures that can trigger use-after-free conditions when memory allocation errors occur.

Is CVE-2021-47361 being actively exploited?

No, this vulnerability is not listed in CISA's Known Exploited Vulnerabilities catalog and no public exploits are currently available, though it poses a high severity risk locally.

What versions of Kernel are affected by CVE-2021-47361?

Linux kernel versions 5.11 through 5.14.8 are vulnerable; kernel 5.14.9 and later contain the fix.

How do I check if my server is vulnerable to CVE-2021-47361?

Run `uname -r` to display your kernel version; if it falls between 5.11 and 5.14.8 (inclusive), your system is vulnerable. Cross-reference with `cat /etc/os-release` to confirm your distribution.

Does Defensia detect CVE-2021-47361?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If the Linux kernel is installed on a monitored server, CVE-2021-47361 will appear in your dashboard with remediation steps.

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References

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