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CVE Record

CVE-2021-47365: afs: Fix page leak

In the Linux kernel, the following vulnerability has been resolved: afs: Fix page leak There's a loop in afs_extend_writeback() that adds extra pages to a write we want to make to improve the efficiency of the writeback by making it larger. This loop stops, however, if we hit a page we can't write back from immediately, but it doesn't get rid of the page ref we speculatively acquired. This was caused by the removal of the cleanup loop when the code switched from using find_get_pages_contig() to xarray scanning as the latter only gets a single page at a time, not a batch. Fix this by putting the page on a ref on an early break from the loop. Unfortunately, we can't just add that page to the pagevec we're employing as we'll go through that and add those pages to the RPC call. This was found by the generic/074 test. It leaks ~4GiB of RAM each time it is run - which can be observed with "top".

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

This Linux kernel issue is a memory leak in the AFS filesystem writeback path. Under the affected condition, pages are not released after an early loop exit, causing significant RAM loss. The source notes about 4 GiB leaked per generic/074 test run, making availability the main concern.

Executive priority

Treat this as a targeted availability risk, not an internet-wide emergency based on available evidence. Patch through normal kernel maintenance, with higher priority for systems using AFS or sensitive to memory exhaustion.

Technical view

In afs_extend_writeback(), speculative page references acquired during xarray scanning were not released when the loop stopped early on a page that could not be written back immediately. The fix releases that page reference on early break. The issue was introduced during a change away from find_get_pages_contig().

Likely exposure

Exposure appears limited to Linux systems running affected kernel versions with the in-kernel AFS filesystem path reachable. The record identifies Linux 5.13-era affected versions and stable fixes around 5.14.9 and 5.15. Validate against vendor kernel backports rather than upstream version strings alone.

Exploitation context

The provided sources do not show active exploitation, public exploit tooling, or KEV listing. Evidence supports a denial-of-service style risk through memory exhaustion in the AFS writeback path, demonstrated by kernel testing, not a documented real-world attack campaign.

Researcher notes

The record lacks CVSS, CWE, exploit status, and detailed affected distribution mapping. The strongest evidence is the upstream kernel description and stable commits. Research should focus on reachability of afs_extend_writeback() in deployed configurations and whether downstream vendors backported the fix.

Mitigation direction

  • Apply vendor kernel updates containing the referenced AFS page leak fix.
  • Prioritize hosts using AFS or kernels with AFS enabled.
  • Check distribution advisories for backported fixes to older kernel package versions.
  • If AFS is unused, consider disabling or avoiding AFS exposure per vendor guidance.

Validation and detection

  • Inventory kernel versions and vendor package release notes for the referenced fix.
  • Confirm whether AFS support is enabled or loaded on affected Linux hosts.
  • Review memory pressure incidents on systems using AFS writeback workloads.
  • Track remediation through normal kernel patch compliance reporting.
Prepared
Confidence
medium
Sources
4

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

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CVE-2021-47365 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
3Source 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

CISA-ADPCISA ADP Vulnrichment
other:ssvc
CVECVE Program Container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinuxe87b03f5830ecd8ca21836d3ee48c74f8d58fa31, e87b03f5830ecd8ca21836d3ee48c74f8d58fa31unaffected
LinuxLinux5.13, 0, 5.14.9, 5.15affected
Weakness

CWE details

No CWE listed

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