high CVSS 7.8 EPSS <0.1%

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

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 3% 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-2021-47049 scores 7.8 on CVSS, so a successful attack would be serious — but at <0.1%, 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: 5.12

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.

Related Kernel CVEs

CVE-2026-63795CVSS 10In the Linux kernel, the following vulnerability has been resolved: 9p: avoid putting oldfid in p9_client_walk() error path When p9_client_walk() is called with clone set to false, fid aliases oldfid. If the walk subsequently fails after the request has been sent, the error path jumps to clunk_fid, which currently calls p9_fid_put(fid) unconditionally. This drops a reference to oldfid even though ownership of oldfid remains with the caller. If this is the last reference, oldfid can be clunked and destroyed while the caller still expects it to be valid. A later use or put of oldfid can then trigger a use-after-free or refcount underflow. Fix this by only putting fid in the clunk_fid error path when it does not alias oldfid, matching the existing guard in the error path below. This can be triggered when a multi-component walk is split into multiple p9_client_walk() calls and a later non-cloning walk fails. A reproducer and refcount warning logs are available on request.
CVE-2026-52955CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: libceph: Fix potential out-of-bounds access in crush_decode() A message of type CEPH_MSG_OSD_MAP containing a crush map with at least one bucket has two fields holding the bucket algorithm. If the values in these two fields differ, an out-of-bounds access can occur. This is the case because the first algorithm field (alg) is used to allocate the correct amount of memory for a bucket of this type, while the second algorithm field inside the bucket (b->alg) is used in the subsequent processing. This patch fixes the issue by adding a check that compares alg and b->alg and aborts the processing in case they differ. Furthermore, b->alg is set to 0 in this case, because the destruction of the crush map also uses this field to determine the bucket type, which can again result in an out-of-bounds access when trying to free the memory pointed to by the fields of the bucket. To correctly free the memory allocated for the bucket in such a case, the corresponding call to kfree is moved from the algorithm-specific crush_destroy_bucket functions to the generic crush_destroy_bucket().
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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