medium CVSS 5.5 EPSS <0.1%

CVE-2021-47395·Kernel vulnerability

In the Linux kernel, the following vulnerability has been resolved: mac80211: limit injected vht mcs/nss in ieee80211_parse_tx_radiotap Limit max values for vht mcs and nss in ieee80211_parse_tx_radiotap routine in order to fix the following warning reported by syzbot: WARNING: CPU: 0 PID: 10717 at include/net/mac80211.h:989 ieee80211_rate_set_vht include/net/mac80211.h:989 [inline] WARNING: CPU: 0 PID: 10717 at include/net/mac80211.h:989 ieee80211_parse_tx_radiotap+0x101e/0x12d0 net/mac80211/tx.c:2244 Modules linked in: CPU: 0 PID: 10717 Comm: syz-executor.5 Not tainted 5.14.0-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 RIP: 0010:ieee80211_rate_set_vht include/net/mac80211.h:989 [inline] RIP: 0010:ieee80211_parse_tx_radiotap+0x101e/0x12d0 net/mac80211/tx.c:2244 RSP: 0018:ffffc9000186f3e8 EFLAGS: 00010216 RAX: 0000000000000618 RBX: ffff88804ef76500 RCX: ffffc900143a5000 RDX: 0000000000040000 RSI: ffffffff888f478e RDI: 0000000000000003 RBP: 00000000ffffffff R08: 0000000000000000 R09: 0000000000000100 R10: ffffffff888f46f9 R11: 0000000000000000 R12: 00000000fffffff8 R13: ffff88804ef7653c R14: 0000000000000001 R15: 0000000000000004 FS: 00007fbf5718f700(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000001b2de23000 CR3: 000000006a671000 CR4: 00000000001506f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600 Call Trace: ieee80211_monitor_select_queue+0xa6/0x250 net/mac80211/iface.c:740 netdev_core_pick_tx+0x169/0x2e0 net/core/dev.c:4089 __dev_queue_xmit+0x6f9/0x3710 net/core/dev.c:4165 __bpf_tx_skb net/core/filter.c:2114 [inline] __bpf_redirect_no_mac net/core/filter.c:2139 [inline] __bpf_redirect+0x5ba/0xd20 net/core/filter.c:2162 ____bpf_clone_redirect net/core/filter.c:2429 [inline] bpf_clone_redirect+0x2ae/0x420 net/core/filter.c:2401 bpf_prog_eeb6f53a69e5c6a2+0x59/0x234 bpf_dispatcher_nop_func include/linux/bpf.h:717 [inline] __bpf_prog_run include/linux/filter.h:624 [inline] bpf_prog_run include/linux/filter.h:631 [inline] bpf_test_run+0x381/0xa30 net/bpf/test_run.c:119 bpf_prog_test_run_skb+0xb84/0x1ee0 net/bpf/test_run.c:663 bpf_prog_test_run kernel/bpf/syscall.c:3307 [inline] __sys_bpf+0x2137/0x5df0 kernel/bpf/syscall.c:4605 __do_sys_bpf kernel/bpf/syscall.c:4691 [inline] __se_sys_bpf kernel/bpf/syscall.c:4689 [inline] __x64_sys_bpf+0x75/0xb0 kernel/bpf/syscall.c:4689 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x44/0xae RIP: 0033:0x4665f9

Severity
medium
Software
Kernel
Fixed in
5.14.10
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 2% 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: 5.14.10

Fixed in: 5.14.10

How to fix this CVE

Update your Linux kernel to version 5.14.10 or later to patch CVE-2021-47395, which addresses improper validation of VHT MCS/NSS parameters in radiotap packet injection. This vulnerability can cause kernel warnings and potential denial of service when malformed wireless frames are injected through monitor mode interfaces. Apply the update through your distribution's package manager and reboot to activate the patched kernel.

sudo dnf update kernel kernel-devel && sudo reboot

Defensia detects this vulnerability

How to check if you are affected

  1. Check kernel version: uname -r (vulnerable if output shows version between 5.11 and 5.14.9)
  2. Verify mac80211 driver is loaded: lsmod | grep mac80211 (confirms wireless frame injection capability)
  3. Search kernel logs for VHT rate warnings: dmesg | grep -i 'ieee80211_rate_set_vht\|vht mcs\|WARNING.*mac80211'
  4. Confirm patch applied: grep -A 5 'ieee80211_parse_tx_radiotap' /boot/System.map-$(uname -r) && verify kernel version is 5.14.10+ with uname -r

FAQ

What is CVE-2021-47395?

CVE-2021-47395 is a kernel vulnerability in mac80211 wireless driver that fails to validate maximum VHT (Very High Throughput) MCS and NSS parameters when processing radiotap-injected packets. Attackers can trigger kernel warnings and denial of service by sending malformed wireless frames through monitor mode interfaces.

Is CVE-2021-47395 being actively exploited?

No, CVE-2021-47395 is not listed in CISA's Known Exploited Vulnerabilities catalog and no public exploits are available. However, the vulnerability can be triggered through local wireless packet injection.

What versions of Kernel are affected by CVE-2021-47395?

Linux kernel versions 5.11.0 through 5.14.9 are vulnerable. Version 5.14.10 and later contain the fix.

How do I check if my server is vulnerable to CVE-2021-47395?

Run: uname -r | grep -E '5\.(11|12|13|14\.[0-9]\b)' && echo 'Vulnerable' || echo 'Patched or unaffected' (checks if running kernel falls in vulnerable range)

Does Defensia detect CVE-2021-47395?

Yes — Defensia's CVE advisory scanner compares installed kernel package versions against the NVD database. If Linux kernel is installed on a monitored server, CVE-2021-47395 will appear in your dashboard with remediation steps.

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References

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