NVD / CVE Program· CNA Linux

CVE-2021-4440: x86/xen: Drop USERGS_SYSRET64 paravirt call

Noroxi assessment

Priority: Monitor (action score 35/100)

The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
Probability of exploitation in the next 30 days: 0.22% (FIRST EPSS).
Someone with local access to the system can trigger it. A low-privileged account is enough. No user action is required. No special conditions are required; it is repeatable.
Fixed version: Linux Linux 1424ab4bb386df9cc590c73afa55f13e9b00dea2, 5.10.218.
Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Low priority for now. Upgrade to Linux Linux 1424ab4bb386df9cc590c73afa55f13e9b00dea2, 5.10.218 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

In the Linux kernel, the following vulnerability has been resolved: x86/xen: Drop USERGS_SYSRET64 paravirt call commit afd30525a659ac0ae0904f0cb4a2ca75522c3123 upstream. USERGS_SYSRET64 is used to return from a syscall via SYSRET, but a Xen PV guest will nevertheless use the IRET hypercall, as there is no sysret PV hypercall defined. So instead of testing all the prerequisites for doing a sysret and then mangling the stack for Xen PV again for doing an iret just use the iret exit from the beginning. This can easily be done via an ALTERNATIVE like it is done for the sysenter compat case already. It should be noted that this drops the optimization in Xen for not restoring a few registers when returning to user mode, but it seems as if the saved instructions in the kernel more than compensate for this drop (a kernel build in a Xen PV guest was slightly faster with this patch applied). While at it remove the stale sysret32 remnants. [ pawan: Brad Spengler and Salvatore Bonaccorso <carnil@debian.org> reported a problem with the 5.10 backport commit edc702b4a820 ("x86/entry_64: Add VERW just before userspace transition"). When CONFIG_PARAVIRT_XXL=y, CLEAR_CPU_BUFFERS is not executed in syscall_return_via_sysret path as USERGS_SYSRET64 is runtime patched to: .cpu_usergs_sysret64 = { 0x0f, 0x01, 0xf8, 0x48, 0x0f, 0x07 }, // swapgs; sysretq which is missing CLEAR_CPU_BUFFERS. It turns out dropping USERGS_SYSRET64 simplifies the code, allowing CLEAR_CPU_BUFFERS to be explicitly added to syscall_return_via_sysret path. Below is with CONFIG_PARAVIRT_XXL=y and this patch applied: syscall_return_via_sysret: ... <+342>: swapgs <+345>: xchg %ax,%ax <+347>: verw -0x1a2(%rip) <------ <+354>: sysretq ]

HighCVSS 8.8 · v3.1—No exploit Fix available

Denial of service

Published: Jun 25, 2024
Updated: Jun 17, 2026
EPSS: 0.2% · 13th percentile
CWE: CWE-400

Report tools

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Action score

Monitor

Low priority for now.

CVSS: 35 / 40 · 8.8 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.2%

CISA SSVC decision

Exploitation: none
Automatable: no
Technical impact: total

Vulnrichment: CISA's decision-tree inputs.

Get told when this record changes

Not in KEV: no record of exploitation in the wild
No public exploit code on record
A fix has been released

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

Vendor	Product	CPE
linux	linux kernel	cpe:2.3:o:linux:linux_kernel

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

linux linux kernel5.10.215 and later · before 5.10.218

Versions reported by the vendor

Affected version ranges reported by the assigning authority (Linux). Independent of NVD's CPE analysis and usually ahead of it.

Linux Linux
- cea750c99d8f6391080c420f811a46b21bad7cf4 and later · before 1424ab4bb386df9cc590c73afa55f13e9b00dea2affected · git
- 5.10.215 and later · before 5.10.218affected · semver

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Ecosystem	Package	Affected range	Fix
Debian:11	linux	before 5.10.218-1	5.10.218-1
SUSE:Linux Enterprise High Availability Extension 12 SP5	kernel-default	before 4.12.14-122.228.1	4.12.14-122.228.1
SUSE:Linux Enterprise Live Patching 12 SP5	kgraft-patch-SLE12-SP5_Update_60	before 1-8.3.1	1-8.3.1
SUSE:Linux Enterprise Real Time 12 SP5	kernel-rt	before 4.12.14-10.200.1	4.12.14-10.200.1
SUSE:Linux Enterprise Real Time 12 SP5	kernel-rt_debug	before 4.12.14-10.200.1	4.12.14-10.200.1
SUSE:Linux Enterprise Real Time 12 SP5	kernel-source-rt	before 4.12.14-10.200.1	4.12.14-10.200.1
SUSE:Linux Enterprise Real Time 12 SP5	kernel-syms-rt	before 4.12.14-10.200.1	4.12.14-10.200.1
SUSE:Linux Enterprise Server 12 SP5	kernel-azure	before 4.12.14-16.197.1	4.12.14-16.197.1
SUSE:Linux Enterprise Server 12 SP5	kernel-source	before 4.12.14-122.228.1	4.12.14-122.228.1
SUSE:Linux Enterprise Server 12 SP5	kernel-source-azure	before 4.12.14-16.197.1	4.12.14-16.197.1
SUSE:Linux Enterprise Server 12 SP5	kernel-syms	before 4.12.14-122.228.1	4.12.14-122.228.1
SUSE:Linux Enterprise Server 12 SP5	kernel-syms-azure	before 4.12.14-16.197.1	4.12.14-16.197.1
SUSE:Linux Enterprise Software Development Kit 12 SP5	kernel-docs	before 4.12.14-122.228.2	4.12.14-122.228.2
SUSE:Linux Enterprise Software Development Kit 12 SP5	kernel-obs-build	before 4.12.14-122.228.2	4.12.14-122.228.2

Same product

linux: all records

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Published before and after this one in the same product

← EarlierCVE-2024-34027Jun 24, 2024 · f2fs: compress: fix to cover {reserve,release}_compress_blocks() w/ cp_rwsem lock
31Monitor
← EarlierCVE-2024-39292Jun 24, 2024 · um: Add winch to winch_handlers before registering winch IRQ
22Monitor
Later →CVE-2022-48772Jun 25, 2024 · media: lgdt3306a: Add a check against null-pointer-def
22Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / package	Fixed version	Source
Linux Linux	1424ab4bb386df9cc590c73afa55f13e9b00dea2	Vendor (CNA)
Linux Linux	5.10.218	Vendor (CNA)
debian:linux	5.10.218-1 · Debian:11	Package registry (OSV)
suse:kernel-azure	4.12.14-16.197.1 · SUSE:Linux Enterprise Server 12 SP5	Package registry (OSV)
suse:kernel-default	4.12.14-122.228.1 · SUSE:Linux Enterprise High Availability Extension 12 SP5	Package registry (OSV)
suse:kernel-docs	4.12.14-122.228.2 · SUSE:Linux Enterprise Software Development Kit 12 SP5	Package registry (OSV)
suse:kernel-obs-build	4.12.14-122.228.2 · SUSE:Linux Enterprise Software Development Kit 12 SP5	Package registry (OSV)
suse:kernel-rt	4.12.14-10.200.1 · SUSE:Linux Enterprise Real Time 12 SP5	Package registry (OSV)
suse:kernel-rt_debug	4.12.14-10.200.1 · SUSE:Linux Enterprise Real Time 12 SP5	Package registry (OSV)
suse:kernel-source	4.12.14-122.228.1 · SUSE:Linux Enterprise Server 12 SP5	Package registry (OSV)
suse:kernel-source-azure	4.12.14-16.197.1 · SUSE:Linux Enterprise Server 12 SP5	Package registry (OSV)
suse:kernel-source-rt	4.12.14-10.200.1 · SUSE:Linux Enterprise Real Time 12 SP5	Package registry (OSV)
suse:kernel-syms	4.12.14-122.228.1 · SUSE:Linux Enterprise Server 12 SP5	Package registry (OSV)
suse:kernel-syms-rt	4.12.14-10.200.1 · SUSE:Linux Enterprise Real Time 12 SP5	Package registry (OSV)
suse:kgraft-patch-SLE12-SP5_Update_60	1-8.3.1 · SUSE:Linux Enterprise Live Patching 12 SP5	Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

CVE-2024-394620 days apartclk: bcm: dvp: Assign ->num before accessing ->hws
39Monitor
CVE-2021-4731335 days apartcpufreq: CPPC: Fix potential memleak in cppc_cpufreq_cpu_init
33Monitor
CVE-2024-386166 days apartwifi: carl9170: re-fix fortified-memset warning
32Monitor
CVE-2021-47023118 days apartnet: marvell: prestera: fix port event handling on init
32Monitor
CVE-2024-383841 days apartblk-cgroup: fix list corruption from reorder of WRITE ->lqueued
31Monitor
CVE-2022-487165 days apartASoC: codecs: wcd938x: fix incorrect used of portid
31Monitor

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

National notice (Türkiye Cybersecurity Directorate / USOM)

Official security notices citing this record; remediation advice is on the agency's page.

TR-24-0790 · Jun 26, 2024(Linux Kernel Güncellemesi)

All national notices →

Technical details

Attack conditions

Someone with local access to the system can trigger it.
A low-privileged account is enough.
No user action is required.
No special conditions are required; it is repeatable.

If successful

Confidentiality: high · data can be read
Integrity: high · data or configuration can be modified
Availability: high · the service can be disrupted

Impact can extend beyond the vulnerable component (scope changes).

Attack vector: Local
Attack complexity: Low
Privileges required: Low
User interaction: None
Scope: Changed
Confidentiality impact: High
Integrity impact: High
Availability impact: High

Weakness class (CWE)

CWE-400 · Uncontrolled Resource Consumption

CVSS vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

nvd-secondary

Root cause

Code that parses nested structures sets no depth or size limit. A small input can turn into a disproportionate processing load.

The bug in code

The whole CWE-400 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1function expand(node) {
2  return node.children.map(expand);
3}

Fixed

1const MAX_DEPTH = 32;
2function expand(node, depth = 0) {
3  if (depth > MAX_DEPTH) throw new Error("too deep");
4  return node.children.map((c) => expand(c, depth + 1));
5}