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PatchSiren cyber security CVE debrief

CVE-2026-89647 Linux CVE debrief

A Linux kernel vulnerability was resolved, addressing a busy loop issue in the ceph_cap_reclaim_work() function. This fix prevents repeated calls to ceph_trim_dentries() when no progress is possible, which could consume CPU without making progress. The issue arises from ceph_cap_reclaim_work() re-queuing itself as long as ceph_trim_dentries() returns -EAGAIN, indicating no progress. The fix involves modifying the function to handle such scenarios more efficiently, preventing CPU consumption without progress.

Vendor
Linux
Product
Unknown
CVSS
HIGH 7.5
CISA KEV
Not listed in stored evidence
Original CVE published
2026-09-11
Original CVE updated
2026-10-21
Advisory published
2026-09-11
Advisory updated
2026-10-21

Who should care

Linux kernel developers and administrators responsible for maintaining and securing Linux systems using ceph. These individuals should review and apply the patch to prevent potential performance degradation or denial of service. They should also monitor Linux kernel updates for further fixes and advisories, and assess exposure and apply compensating controls if necessary.

Why it matters

This vulnerability fix prevents a busy loop issue in the Linux kernel's ceph_cap_reclaim_work() function, which could consume CPU without making progress. Linux kernel developers and administrators should review and apply the patch to prevent potential performance degradation or denial of service.

  • Preventing CPU consumption without progress in ceph_cap_reclaim_work()
  • Reducing the risk of performance degradation or denial of service

Technical summary

The Linux kernel's ceph_cap_reclaim_work() function was modified to prevent a busy loop when no progress is possible. The fix addresses an issue where the function would repeatedly call ceph_trim_dentries() without making progress, consuming CPU. This was achieved by changing the function's behavior to handle scenarios where no progress is possible more efficiently, thus preventing unnecessary CPU consumption. The fix ensures that the function no longer enters a loop that consumes CPU without making progress, addressing the vulnerability.

Defensive priority

Medium

Recommended defensive actions

  • Review and apply the patch to prevent the busy loop issue
  • Monitor Linux kernel updates for further fixes and advisories
  • Assess exposure and apply compensating controls if necessary
  • Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up.
  • Review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance.
  • Plan vendor-supported updates or mitigations through normal change control where exposure is confirmed.
  • Check relevant monitoring, detection, and logs for exposed assets that need extra review.

Evidence notes

The CVE record and source item provide details on the vulnerability and its fix. The Linux kernel's ceph_cap_reclaim_work() function was modified to prevent a busy loop when no progress is possible. The fix addresses an issue where the function would repeatedly call ceph_trim_dentries() without making progress, consuming CPU. This information is based on the provided CVE record and source item, which outline the vulnerability and the implemented fix.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-89647 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-89647

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-89647 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-89647

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

  • ceph: do not repeat ceph_trim_dentries() if no progress possible

    Unverified legacy reference

    URL: https://raw.githubusercontent.com/CVEProject/cvelistV5/main/cves/2026/89xxx/CVE-2026-89647.json

    cve_program_cvelist_v5

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/dd2e9824e5e7dba406005ff779a107f773175a76

    Supplemental source

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/5a541eb401acb89d791da41189d7a79220164b93

    Supplemental source

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/37d6edb2f03b29399a3a337fae78674de51e1695

    Supplemental source

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/3d122b2feb1dd76bb5041bdea5e1e1b007d8d415

    Supplemental source

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/e7d7aa7b730178278109c41fa1b17b06873065d5

    Supplemental source

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.