high CVSS 7.8

CVE-2021-47049·Kernel vulnerability

In the Linux kernel, the following vulnerability has been resolved: Drivers: hv: vmbus: Use after free in __vmbus_open() The "open_info" variable is added to the &vmbus_connection.chn_msg_list, but the error handling frees "open_info" without removing it from the list. This will result in a use after free. First remove it from the list, and then free it.

Severity
high
Software
Kernel
Fixed in
5.12.4
Published
2024-02-28

Affected versions

From: 5.12

Until: 5.12.4

Fixed in: 5.12.4

How to fix this CVE

Update your Linux kernel to version 5.12.4 or later to resolve a use-after-free vulnerability in the Hyper-V vmbus driver. This flaw occurs when error handling in __vmbus_open() frees memory without first removing it from an active linked list, potentially causing kernel crashes or memory corruption. Apply the patch immediately on systems running affected kernel versions 5.12 through 5.12.3.

sudo dnf update kernel kernel-devel

Defensia detects this vulnerability

How to check if you are affected

  1. Step 1: Check kernel version with `uname -r` and confirm if it falls between 5.12 and 5.12.3
  2. Step 2: Verify Hyper-V vmbus driver is loaded with `lsmod | grep hv_vmbus` — if output is empty, the component is not exposed
  3. Step 3: Search kernel logs for vmbus-related crashes with `dmesg | grep -i 'vmbus\|use.after.free' | tail -20` or check `/var/log/kern.log`
  4. Step 4: After patching, reboot and confirm new kernel version with `uname -r` returns 5.12.4 or later

FAQ

What is CVE-2021-47049?

CVE-2021-47049 is a use-after-free vulnerability in the Linux kernel's Hyper-V vmbus driver. The error handling path frees memory structures without removing them from an active list, allowing subsequent access to deallocated memory.

Is CVE-2021-47049 being actively exploited?

No, there are no known public exploits or active exploitation attempts documented for this vulnerability according to CISA KEV tracking.

What versions of Kernel are affected by CVE-2021-47049?

Linux kernel versions 5.12 through 5.12.3 are vulnerable. Version 5.12.4 and later contain the fix.

How do I check if my server is vulnerable to CVE-2021-47049?

Run `uname -r` to check your kernel version. If it shows 5.12.0 through 5.12.3 and `lsmod | grep hv_vmbus` shows the driver is loaded, your system is vulnerable.

Does Defensia detect CVE-2021-47049?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Kernel is installed on a monitored server, CVE-2021-47049 will appear in your dashboard with remediation steps.

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References

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