medium CVSS 5.5 EPSS <0.1%

CVE-2021-47276·Kernel vulnerability

In the Linux kernel, the following vulnerability has been resolved: ftrace: Do not blindly read the ip address in ftrace_bug() It was reported that a bug on arm64 caused a bad ip address to be used for updating into a nop in ftrace_init(), but the error path (rightfully) returned -EINVAL and not -EFAULT, as the bug caused more than one error to occur. But because -EINVAL was returned, the ftrace_bug() tried to report what was at the location of the ip address, and read it directly. This caused the machine to panic, as the ip was not pointing to a valid memory address. Instead, read the ip address with copy_from_kernel_nofault() to safely access the memory, and if it faults, report that the address faulted, otherwise report what was in that location.

Severity
medium
Software
Kernel
Fixed in
5.12.11
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: 5.12.11

Fixed in: 5.12.11

How to fix this CVE

Update your Linux kernel to version 5.12.11 or later to patch this vulnerability that could cause kernel panics during ftrace initialization on ARM64 systems. The fix implements safe memory access using copy_from_kernel_nofault() instead of direct pointer dereferencing, preventing machine crashes when invalid instruction pointers are encountered during ftrace error handling.

sudo dnf update kernel kernel-devel

Defensia detects this vulnerability

How to check if you are affected

  1. Check installed kernel version: uname -r (should be 5.12.11 or later if patched)
  2. Verify kernel configuration has ftrace enabled: grep CONFIG_FTRACE /boot/config-$(uname -r)
  3. Monitor system logs for ftrace-related panics: sudo dmesg | grep -i ftrace
  4. Confirm patch applied by checking kernel commit: git log --oneline | grep -i 'ftrace.*nofault' or verify kernel build timestamp is after the patch release date

FAQ

What is CVE-2021-47276?

This vulnerability exists in the Linux kernel's ftrace subsystem where error handling code directly reads memory at an invalid instruction pointer address without safety checks, causing kernel panics on ARM64 systems during ftrace initialization failures.

Is CVE-2021-47276 being actively exploited?

No, this CVE is not listed on the CISA Known Exploited Vulnerabilities catalog and no public exploits are available. Exploitation would require local access and specific kernel configuration.

What versions of Kernel are affected by CVE-2021-47276?

Linux kernel versions 5.11 through 5.12.10 are vulnerable; the fix is available in 5.12.11 and later stable releases.

How do I check if my server is vulnerable to CVE-2021-47276?

Run uname -r to retrieve your kernel version; if it shows 5.11.x or 5.12.0 through 5.12.10, your system is vulnerable. Verify ftrace is enabled with grep CONFIG_FTRACE /boot/config-$(uname -r).

Does Defensia detect CVE-2021-47276?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Kernel is installed on a monitored server, CVE-2021-47276 will appear in your dashboard with remediation steps.

Related Kernel CVEs

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CVE-2026-53384CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: serial: 8250_dw: unregister 8250 port if clk_notifier_register() fails dw8250_probe() registers the 8250 port via serial8250_register_8250_port() and then, if the device has a clock, registers a clock notifier. If clk_notifier_register() fails, probe returns the error but leaves the 8250 port registered. The matching serial8250_unregister_port() lives in dw8250_remove(), which is not called when probe fails, so the port slot stays occupied until the device is rebound or the system is rebooted. The devm-allocated driver data is freed while the port still references it (via the saved private_data and serial_in/serial_out callbacks), so any access to that port slot before a rebind is a use-after-free hazard. Unregister the port on the clk_notifier_register() error path.
CVE-2026-52931CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: batman-adv: tp_meter: avoid use of uninit sender vars batadv_tp_recv_ack() and batadv_tp_stop() are only valid for tp_vars in the BATADV_TP_SENDER role. When called with a BATADV_TP_RECEIVER role, it proceeds to read sender-only members that were never initialized, leading to undefined behavior. This can be triggered when a node that is currently acting as a receiver in an ongoing tp_meter session receives a malicious ACK packet. Guard against this by checking tp_vars->role immediately after the lookup and bailing out if it is not BATADV_TP_SENDER, before any of those members are accessed.
CVE-2026-52982CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: net: usb: rtl8150: fix use-after-free in rtl8150_start_xmit() syzbot reported a KASAN slab-use-after-free read in rtl8150_start_xmit() when accessing skb->len for tx statistics after usb_submit_urb() has been called: BUG: KASAN: slab-use-after-free in rtl8150_start_xmit+0x71f/0x760 drivers/net/usb/rtl8150.c:712 Read of size 4 at addr ffff88810eb7a930 by task kworker/0:4/5226 The URB completion handler write_bulk_callback() frees the skb via dev_kfree_skb_irq(dev->tx_skb). The URB may complete on another CPU in softirq context before usb_submit_urb() returns in the submitter, so by the time the submitter reads skb->len the skb has already been queued to the per-CPU completion_queue and freed by net_tx_action(): CPU A (xmit) CPU B (USB completion softirq) ------------ ------------------------------ dev->tx_skb = skb; usb_submit_urb() --+ |-------> write_bulk_callback() | dev_kfree_skb_irq(dev->tx_skb) | net_tx_action() | napi_skb_cache_put() <-- free netdev->stats.tx_bytes | += skb->len; <-- UAF read Fix it by caching skb->len before submitting the URB and using the cached value when updating the tx_bytes counter. The pre-existing tx_bytes semantics are preserved: the counter tracks the original frame length (skb->len), not the ETH_ZLEN/USB-alignment padded "count" value that is handed to the device. Changing that would be a user-visible accounting change and is out of scope for this UAF fix.

References

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