NVD / CVE Program· CNA Linux

CVE-2021-47277: kvm: avoid speculation-based attacks from out-of-range memslot accesses

Noroxi assessment

Priority: Monitor (action score 28/100)

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: 0.25% (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 22b87fb17a28d37331bb9c1110737627b17f6781, 3098b86390a6b9ea52657689f08410baf130ceff, 361ce3b917aff93123e9e966d8608655c967f438.
Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Low priority for now. Upgrade to Linux Linux 22b87fb17a28d37331bb9c1110737627b17f6781, 3098b86390a6b9ea52657689f08410baf130ceff, 361ce3b917aff93123e9e966d8608655c967f438 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: kvm: avoid speculation-based attacks from out-of-range memslot accesses KVM's mechanism for accessing guest memory translates a guest physical address (gpa) to a host virtual address using the right-shifted gpa (also known as gfn) and a struct kvm_memory_slot. The translation is performed in __gfn_to_hva_memslot using the following formula: hva = slot->userspace_addr + (gfn - slot->base_gfn) * PAGE_SIZE It is expected that gfn falls within the boundaries of the guest's physical memory. However, a guest can access invalid physical addresses in such a way that the gfn is invalid. __gfn_to_hva_memslot is called from kvm_vcpu_gfn_to_hva_prot, which first retrieves a memslot through __gfn_to_memslot. While __gfn_to_memslot does check that the gfn falls within the boundaries of the guest's physical memory or not, a CPU can speculate the result of the check and continue execution speculatively using an illegal gfn. The speculation can result in calculating an out-of-bounds hva. If the resulting host virtual address is used to load another guest physical address, this is effectively a Spectre gadget consisting of two consecutive reads, the second of which is data dependent on the first. Right now it's not clear if there are any cases in which this is exploitable. One interesting case was reported by the original author of this patch, and involves visiting guest page tables on x86. Right now these are not vulnerable because the hva read goes through get_user(), which contains an LFENCE speculation barrier. However, there are patches in progress for x86 uaccess.h to mask kernel addresses instead of using LFENCE; once these land, a guest could use speculation to read from the VMM's ring 3 address space. Other architectures such as ARM already use the address masking method, and would be susceptible to this same kind of data-dependent access gadgets. Therefore, this patch proactively protects from these attacks by masking out-of-bounds gfns in __gfn_to_hva_memslot, which blocks speculation of invalid hvas. Sean Christopherson noted that this patch does not cover kvm_read_guest_offset_cached. This however is limited to a few bytes past the end of the cache, and therefore it is unlikely to be useful in the context of building a chain of data dependent accesses.

HighCVSS 7.1 · v3.1—No exploit Fix available

Memory safety

BDU:2025-14604

Published: May 21, 2024
Updated: Jun 17, 2026
EPSS: 0.2% · 17th percentile
CWE: CWE-125

Report tools

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Action score

Monitor

Low priority for now.

CVSS: 28 / 40 · 7.1 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.2%

CISA SSVC decision

Exploitation: none
Automatable: no
Technical impact: partial

Vulnrichment: CISA's decision-tree inputs.

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No public exploit code on record
A fix has been released

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Noroxi analysis

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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 kernelbefore 4.4.273
linux linux kernel4.5 and later · before 4.9.273
linux linux kernel4.10 and later · before 4.14.237
linux linux kernel4.15 and later · before 4.19.195
linux linux kernel4.20 and later · before 5.4.126
linux linux kernel5.5 and later · before 5.10.44
linux linux kernel5.11 and later · before 5.12.11
linux linux kernel5.13

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
- 2.6.25affected
- 8a7ae055f3533b520401c170ac55e30628b34df5 and later · before 3098b86390a6b9ea52657689f08410baf130ceffaffected · git
- 8a7ae055f3533b520401c170ac55e30628b34df5 and later · before 740621309b25bbf619b8a0ba5fd50a8e58989441affected · git
- 8a7ae055f3533b520401c170ac55e30628b34df5 and later · before 361ce3b917aff93123e9e966d8608655c967f438affected · git
- 8a7ae055f3533b520401c170ac55e30628b34df5 and later · before 22b87fb17a28d37331bb9c1110737627b17f6781affected · git
- 8a7ae055f3533b520401c170ac55e30628b34df5 and later · before bff1fbf0cf0712686f1df59a83fba6e31d2746a0affected · git
- 8a7ae055f3533b520401c170ac55e30628b34df5 and later · before 7af299b97734c7e7f465b42a2139ce4d77246975affected · git
- 8a7ae055f3533b520401c170ac55e30628b34df5 and later · before ed0e2a893092c7fcb4ff7ba74e5efce53a6f5940affected · git
- 8a7ae055f3533b520401c170ac55e30628b34df5 and later · before da27a83fd6cc7780fea190e1f5c19e87019da65caffected · git
- before 2.6.25not affected · semver

Package-level exposure

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

Ecosystem	Package	Affected range	Fix
Debian:12	linux	before 5.10.46-1	5.10.46-1

Same product

linux: all records

Other highest-scoring records for the same primary product.

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Published before and after this one in the same product

← EarlierCVE-2021-47275May 21, 2024 · bcache: avoid oversized read request in cache missing code path
22Monitor
← EarlierCVE-2021-47276May 21, 2024 · ftrace: Do not blindly read the ip address in ftrace_bug()
22Monitor
Later →CVE-2021-47278May 21, 2024 · bus: mhi: pci_generic: Fix possible use-after-free in mhi_pci_remove()
31Monitor

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	22b87fb17a28d37331bb9c1110737627b17f6781	Vendor (CNA)
Linux Linux	3098b86390a6b9ea52657689f08410baf130ceff	Vendor (CNA)
Linux Linux	361ce3b917aff93123e9e966d8608655c967f438	Vendor (CNA)
Linux Linux	740621309b25bbf619b8a0ba5fd50a8e58989441	Vendor (CNA)
Linux Linux	7af299b97734c7e7f465b42a2139ce4d77246975	Vendor (CNA)
Linux Linux	bff1fbf0cf0712686f1df59a83fba6e31d2746a0	Vendor (CNA)
Linux Linux	da27a83fd6cc7780fea190e1f5c19e87019da65c	Vendor (CNA)
Linux Linux	ed0e2a893092c7fcb4ff7ba74e5efce53a6f5940	Vendor (CNA)
debian:linux	5.10.46-1 · Debian:12	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.

No nightly-computed relations.

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).