medium CVSS 5.5 EPSS <0.1%

CVE-2021-47307·Kernel vulnerability

In the Linux kernel, the following vulnerability has been resolved: cifs: prevent NULL deref in cifs_compose_mount_options() The optional @ref parameter might contain an NULL node_name, so prevent dereferencing it in cifs_compose_mount_options(). Addresses-Coverity: 1476408 ("Explicit null dereferenced")

Severity
medium
Software
Kernel
Fixed in
5.13.5
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 4% 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.

Affected versions

From: 5.11

Until: 5.13.5

Fixed in: 5.13.5

How to fix this CVE

Update your Linux kernel to version 5.13.5 or later to resolve a null pointer dereference vulnerability in the CIFS mount options handling. This issue could lead to kernel denial of service when processing certain mount configurations. Apply the latest kernel patches available for your distribution and reboot to activate the fix.

sudo dnf update kernel kernel-devel

Defensia detects this vulnerability

How to check if you are affected

  1. Check your kernel version: uname -r — Versions 5.11 through 5.13.4 are vulnerable
  2. Verify CIFS module is loaded: lsmod | grep cifs — If present, your system uses the affected code path
  3. Search kernel logs for mount-related crashes: grep -i 'null pointer\|kernel panic\|cifs' /var/log/kern.log or journalctl -k | grep -i cifs
  4. Confirm the fix by checking if the latest kernel patch is applied: cat /proc/version and verify build date is after the patch release date

FAQ

What is CVE-2021-47307?

This vulnerability is a null pointer dereference in the Linux kernel's CIFS (Common Internet File System) mount handling code. When processing mount options with a missing or malformed node name, the kernel could crash, causing a denial of service.

Is CVE-2021-47307 being actively exploited?

No, this vulnerability is not listed as actively exploited in the CISA Known Exploited Vulnerabilities catalog, and no public exploits are available.

What versions of Kernel are affected by CVE-2021-47307?

Linux kernel versions 5.11 through 5.13.4 are vulnerable. Version 5.13.5 and later include the fix.

How do I check if my server is vulnerable to CVE-2021-47307?

Run uname -r to check your kernel version. If it returns a version between 5.11 and 5.13.4, your system is vulnerable. Cross-reference with lsmod | grep cifs to confirm CIFS support is enabled.

Does Defensia detect CVE-2021-47307?

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-2021-47307 will appear in your dashboard with remediation steps.

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References

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