PT-2024-11037 · Linux+2 · Linux Kernel+2

Brad Spengler · Published 2024-05-25 · Updated 2024-09-16 · CVE-2021-4440

Positive Technologies (AI Summary)

CVSS v3.1

8.8

High

Base vector

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

Name of the Vulnerable Software and Affected Versions Linux kernel (affected versions not specified)

Description The vulnerability is related to the x86/xen paravirt call in the Linux kernel. Specifically, the USERGS SYSRET64 call is used to return from a syscall via SYSRET, but a Xen PV guest will use the IRET hypercall instead, as there is no sysret PV hypercall defined. To resolve this, the USERGS SYSRET64 call is dropped, and the IRET exit is used from the beginning. This change simplifies the code and allows CLEAR CPU BUFFERS to be explicitly added to the syscall return via sysret path.

Recommendations At the moment, there is no information about a newer version that contains a fix for this vulnerability.

Resource Exhaustion

Weakness Enumeration

CWE-400

CWE-99

Related Identifiers

BDU:2025-02846

CVE-2021-4440

SUSE-SU-2024:3189-1

SUSE-SU-2024:3251-1

SUSE-SU-2024:3252-1

SUSE-SU-2024_3189-1

SUSE-SU-2024_3251-1

SUSE-SU-2024_3252-1

Affected Products

Astra Linux

Linux Kernel

Suse

References · 255

• https://osv.dev/vulnerability/CVE-2021-4440 · Vendor Advisory
• https://osv.dev/vulnerability/DEBIAN-CVE-2021-4440 · Vendor Advisory
• https://security-tracker.debian.org/tracker/CVE-2021-4440 · Vendor Advisory
• https://cve.org/CVERecord?id=CVE-2021-4440 · Security Note
• https://wiki.astralinux.ru/astra-linux-se47-bulletin-2025-0422SE101 · Vendor Advisory
• https://bdu.fstec.ru/vul/2025-02846 · Security Note
• https://osv.dev/vulnerability/SUSE-SU-2024:3189-1 · Vendor Advisory
• https://grsecurity.net/cve-2021-4440_linux_cna_case_study · Patch
• https://osv.dev/vulnerability/SUSE-SU-2024:3251-1 · Vendor Advisory
• https://git.kernel.org/stable/c/1424ab4bb386df9cc590c73afa55f13e9b00dea2 · Patch
• https://osv.dev/vulnerability/SUSE-SU-2024:3252-1 · Vendor Advisory
• https://nvd.nist.gov/vuln/detail/CVE-2021-4440 · Security Note
• https://wiki.astralinux.ru/astra-linux-se17-bulletin-2025-0319SE17 · Vendor Advisory
• https://ubuntu.com/security/CVE-2021-4440 · Vendor Advisory
• https://osv.dev/vulnerability/UBUNTU-CVE-2021-4440 · Vendor Advisory