high CVSS 7.8 EPSS 0.23%

CVE-2021-47251·Kernel vulnerability

In the Linux kernel, the following vulnerability has been resolved: mac80211: fix skb length check in ieee80211_scan_rx() Replace hard-coded compile-time constants for header length check with dynamic determination based on the frame type. Otherwise, we hit a validation WARN_ON in cfg80211 later. [style fixes, reword commit message]

Severity
high
Software
Kernel
Fixed in
5.12.13
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 0.23% — higher than 14% 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-2021-47251 scores 7.8 on CVSS, so a successful attack would be serious — but at 0.23%, 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: 5.12.13

Fixed in: 5.12.13

How to fix this CVE

Update your Linux kernel to version 5.12.13 or later to resolve a frame header validation issue in the mac80211 wireless subsystem. This vulnerability affects kernel versions 5.11 through 5.12.12 and can be triggered by local users with sufficient privileges. Apply the latest stable kernel update available for your distribution to patch the dynamic header length validation mechanism.

sudo dnf update kernel kernel-devel

Defensia detects this vulnerability

How to check if you are affected

  1. Check your kernel version: uname -r — verify it is at or above 5.12.13
  2. Confirm mac80211 module is loaded: lsmod | grep mac80211 — if empty, wireless scanning is not active on this system
  3. Review kernel config for wireless support: grep CONFIG_MAC80211 /boot/config-$(uname -r) — should show CONFIG_MAC80211=m or CONFIG_MAC80211=y
  4. Verify patch application by checking kernel build details: cat /proc/version — confirm kernel version matches or exceeds 5.12.13

FAQ

What is CVE-2021-47251?

This vulnerability exists in the mac80211 wireless driver component of the Linux kernel, where improper frame header length validation during wireless scanning operations could trigger internal validation warnings. The flaw stems from using hard-coded header sizes instead of dynamically determining them based on actual frame types.

Is CVE-2021-47251 being actively exploited?

No, this vulnerability is not listed in CISA's Known Exploited Vulnerabilities catalog and no public exploits have been disclosed. However, the high CVSS score of 7.8 reflects the potential for local privilege escalation.

What versions of Kernel are affected by CVE-2021-47251?

Linux kernel versions 5.11.0 through 5.12.12 are vulnerable. Kernel 5.12.13 and later versions contain the fix.

How do I check if my server is vulnerable to CVE-2021-47251?

Run 'uname -r' and compare your kernel version to the vulnerable range 5.11.x through 5.12.12. If your kernel version is lower than 5.12.13, your system is vulnerable.

Does Defensia detect CVE-2021-47251?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Kernel is installed on a monitored server, CVE-2021-47251 will appear in your dashboard with remediation steps.

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References

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