CVE-2021-4440
8.8 · HIGHOverview
CVE-2021-4440 is a high-severity vulnerability affecting linux linux_kernel. It was published on June 25, 2024 and has a CVSS 3.1 base score of 8.8 (HIGH).
This vulnerability has a CVSS 3.1 base score of 8.8, rated HIGH. It requires local or adjacent network access to exploit. Some level of privileges is required for exploitation.
Technical Description
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
Remediation
Check the references section for vendor advisories and patches from linux. Update linux_kernel to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
Affected Products
| Vendor | Product | Versions | Status |
|---|---|---|---|
| linux | linux_kernel | >= 5.10.215, < 5.10.218 | Affected |
Frequently Asked Questions
What is CVE-2021-4440?
CVE-2021-4440 is a high-severity vulnerability affecting linux linux_kernel. It was published on June 25, 2024 and has a CVSS 3.1 base score of 8.8 (HIGH).
How severe is CVE-2021-4440?
This vulnerability has a CVSS 3.1 base score of 8.8, rated HIGH. It requires local or adjacent network access to exploit. Some level of privileges is required for exploitation.
How do I fix or remediate CVE-2021-4440?
Check the references section for vendor advisories and patches from linux. Update linux_kernel to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
How can CyberStrike help with CVE-2021-4440?
CyberStrike's AI-powered security agents can automatically detect CVE-2021-4440 across your infrastructure using autonomous pentesting, DAST scanning, and HackBrowser. The platform continuously monitors for known vulnerabilities and provides actionable remediation guidance prioritized by real-world exploitability.
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