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CVE Record

CVE-2021-47579: ovl: fix warning in ovl_create_real()

In the Linux kernel, the following vulnerability has been resolved: ovl: fix warning in ovl_create_real() Syzbot triggered the following warning in ovl_workdir_create() -> ovl_create_real(): if (!err && WARN_ON(!newdentry->d_inode)) { The reason is that the cgroup2 filesystem returns from mkdir without instantiating the new dentry. Weird filesystems such as this will be rejected by overlayfs at a later stage during setup, but to prevent such a warning, call ovl_mkdir_real() directly from ovl_workdir_create() and reject this case early.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

CVE-2021-47579 is a Linux kernel overlayfs issue where an unusual filesystem behavior could trigger a kernel warning during overlayfs work directory creation. The public record does not describe data loss, privilege escalation, or active exploitation. Treat it as a kernel maintenance and stability issue unless vendor guidance says otherwise.

Executive priority

Handle through normal kernel patch management unless exposed systems show related instability or vendor advisories raise severity. There is no source-backed evidence of active exploitation or high business impact in the provided bundle.

Technical view

The issue is in overlayfs handling in ovl_workdir_create() and ovl_create_real(). A cgroup2 mkdir path can return without instantiating the new dentry, causing a WARN_ON condition. The fix calls ovl_mkdir_real() directly and rejects the invalid case earlier during overlayfs setup.

Likely exposure

Exposure is limited to Linux systems running affected kernel versions or downstream builds that include the vulnerable overlayfs code. Systems using overlayfs, especially container or layered filesystem environments, are the most relevant to review. The source bundle does not identify specific distributions or appliances.

Exploitation context

The bundle reports syzbot triggering the warning, not real-world exploitation. CISA KEV status is false, and no cited source in the bundle states active exploitation, public exploit availability, or weaponized use.

Researcher notes

Evidence is sparse: no CVSS, CWE, exploit details, or impact statement beyond a kernel warning. The useful anchors are the affected kernel ranges, overlayfs/cgroup2 interaction, syzbot discovery context, and stable kernel commit references.

Mitigation direction

  • Apply vendor-supported kernel updates containing the referenced stable fixes.
  • Confirm distribution advisories map the stable commits into your kernel package.
  • Prioritize review of hosts using overlayfs or container filesystem layers.
  • Avoid running affected end-of-life kernels where security fixes are unavailable.

Validation and detection

  • Inventory Linux kernel versions across servers, containers hosts, and appliances.
  • Check kernel changelogs for the referenced overlayfs stable commits.
  • Confirm whether overlayfs is enabled or operationally used on affected hosts.
  • Review kernel logs for overlayfs WARN_ON messages during setup paths.
Prepared
Confidence
medium
Sources
7

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

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CVE-2021-47579 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
3Timeline events
2ADP providers
6Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical Impact: partial

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CVECVE Program Container
CISA-ADPCISA ADP Vulnrichment
other:ssvc

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinuxe9be9d5e76e34872f0c37d72e25bc27fe9e2c54c, e9be9d5e76e34872f0c37d72e25bc27fe9e2c54c, e9be9d5e76e34872f0c37d72e25bc27fe9e2c54c, e9be9d5e76e34872f0c37d72e25bc27fe9e2c54c, e9be9d5e76e34872f0c37d72e25bc27fe9e2c54cunaffected
LinuxLinux3.18, 0, 4.19.222, 5.4.168, 5.10.88, 5.15.11, 5.16affected
Weakness

CWE details

No CWE listed

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.