medium 5.5

CVE-2024-55916 json

Drivers: hv: util: Avoid accessing a ringbuffer not initialized yet

published 2025-01-11 21 mo ago modified 2026-06-17 4 mo ago also EUVD-2024-52846

cvss: 5.5; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.2%; EPSS 0.2% chance of exploitation in 30 days, percentile 13%
public exploits: 0; none known

In the Linux kernel, the following vulnerability has been resolved:

If the KVP (or VSS) daemon starts before the VMBus channel's ringbuffer is fully initialized, we can hit the panic below:

hv_utils: Registering HyperV Utility Driver hv_vmbus: registering driver hv_utils ... BUG: kernel NULL pointer dereference, address: 0000000000000000 CPU: 44 UID: 0 PID: 2552 Comm: hv_kvp_daemon Tainted: G E 6.11.0-rc3+ #1 RIP: 0010:hv_pkt_iter_first+0x12/0xd0 Call Trace: ... vmbus_recvpacket hv_kvp_onchannelcallback vmbus_on_event tasklet_action_common tasklet_action handle_softirqs irq_exit_rcu sysvec_hyperv_stimer0 </IRQ> <TASK> asm_sysvec_hyperv_stimer0 ... kvp_register_done hvt_op_read vfs_read ksys_read __x64_sys_read

This can happen because the KVP/VSS channel callback can be invoked even before the channel is fully opened: 1) as soon as hv_kvp_init() -> hvutil_transport_init() creates /dev/vmbus/hv_kvp, the kvp daemon can open the device file immediately and register itself to the driver by writing a message KVP_OP_REGISTER1 to the file (which is handled by kvp_on_msg() ->kvp_handle_handshake()) and reading the file for the driver's response, which is handled by hvt_op_read(), which calls hvt->on_read(), i.e. kvp_register_done().

2) the problem with kvp_register_done() is that it can cause the channel callback to be called even before the channel is fully opened, and when the channel callback is starting to run, util_probe()-> vmbus_open() may have not initialized the ringbuffer yet, so the callback can hit the panic of NULL pointer dereference.

To reproduce the panic consistently, we can add a "ssleep(10)" for KVP in __vmbus_open(), just before the first hv_ringbuffer_init(), and then we unload and reload the driver hv_utils, and run the daemon manually within the 10 seconds.

Fix the panic by reordering the steps in util_probe() so the char dev entry used by the KVP or VSS daemon is not created until after vmbus_open() has completed. This reordering prevents the race condition from happening.

Patch / fix

fixed in 1 distros 4 links 7

Linux Linux 5.4.289, 5.10.233, 5.15.176, 6.1.122, 6.6.68, 6.12.7, 6.13

debian ubuntu suse azure linux

linux Debian 12 6.1.123-1
linux Debian 14, Debian 13 6.12.8-1

debian advisories DEBIAN-CVE-2024-55916

linux Ubuntu 20.04 LTS 5.4.0-211.231
linux Ubuntu 22.04 LTS 5.15.0-135.146
linux Ubuntu 24.04 LTS 6.8.0-60.63
linux-aws Ubuntu 20.04 LTS 5.4.0-1142.152
linux-aws Ubuntu 22.04 LTS 5.15.0-1080.87
linux-aws Ubuntu 24.04 LTS 6.8.0-1029.31
linux-gcp Ubuntu 20.04 LTS 5.4.0-1145.154
linux-gcp Ubuntu 22.04 LTS 5.15.0-1079.88

ubuntu advisories UBUNTU-CVE-2024-55916

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

kernel-rt Linux Micro 6.1, Linux Micro 6.0 6.4.0-25.1
kernel-source-rt Linux Micro 6.1, Linux Micro 6.0 6.4.0-25.1
kernel-livepatch-MICRO-6-0-RT_Update_5 Linux Micro 6.1, Linux Micro 6.0 1-1.1
kernel-source Linux Micro 6.1, Linux Micro 6.0 6.4.0-25.1
kernel-default Linux Micro 6.1, Linux Micro 6.0 6.4.0-25.1
kernel-kvmsmall Linux Micro 6.1, Linux Micro 6.0 6.4.0-25.1
kernel-default-base Linux Micro 6.1, Linux Micro 6.0 6.4.0-24.1.21.4
kernel-livepatch-MICRO-6-0_Update_5 Linux Micro 6.1, Linux Micro 6.0 1-1.2

suse advisories SUSE-SU-2025:20166-1 SUSE-SU-2025:20249-1 SUSE-SU-2025:20165-1 SUSE-SU-2025:20248-1 SUSE-SU-2025:0577-1 SUSE-SU-2025:0577-2

kernel Azure Linux 3.0 6.6.76.1-1
kernel CBL-Mariner 2.0 5.15.176.3-1

azure linux advisories AZL-55736 AZL-55754

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2024-55916 updated 2026-11-07 cvss 5.5

kernel: Drivers: hv: util: Avoid accessing a ringbuffer not initialized yet

Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 more
affected: no fix planned “Out of support scope”
Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +83 more
not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation: none
Automatable: no
Technical impact: partial
Assessed: 13 mo ago (2025-10-01)

Exploit prediction

0.22% chance of exploitation in the next 30 days, higher than 13% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CISA ADP	3.1	5.5	CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
NVD	3.1	5.5	CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
CNA	3.1	5.5	CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected products

Linux Linux

Classification

Weakness

CWE-476 NULL Pointer Dereference

Technology feeds

Linux kernel rss critical rss

References

Sources

CVE List CVE-2024-55916
NVD CVE-2024-55916

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary