Vulnerability in Linux kernel (CVE-2026-89647)
Summary
Vulnerability in Linux kernel (CVE-2026-89647). Risk of unauthorized operations or information disclosure. Exploitable via nr_to_scan.
Original description
The description as published by the source.
In the Linux kernel, the following vulnerability has been resolved:
ceph: do not repeat ceph_trim_dentries() if no progress possible
ceph_cap_reclaim_work() re-queues itself for as long as
ceph_trim_dentries() returns -EAGAIN, which happens whenever a lease
walk exhausts its nr_to_scan budget. This creates a busy loop that
consumes CPU without making any progress when there is nothing to
reclaim: with no cap pressure (count==0) and every scanned lease
still valid, each pass runs the full scan budget down to zero and
returns -EAGAIN, only to be queued again immediately.
The dir-lease walk made this worse. When expire_dir_lease is
false (i.e. we have no intention of reclaiming dir leases),
__dir_lease_check() returned TOUCH for every valid lease. TOUCH
moves the dentry to the tail of the list and resets di->time via
__dentry_dir_lease_touch(), so a walk over N valid leases pointlessly
rewrote the list, refreshed the timestamps (preventing them from ever
aging out) and always drained nr_to_scan, guaranteeing the -EAGAIN
requeue.
Fix this in three steps:
-
Return
KEEPinstead ofTOUCHwhenexpire_dir_leaseis
false. If we are not going to reclaim the lease, leave it in
place instead of churning the list and resetting its timestamp; the
walk then terminates naturally (or viaSTOPat the first fresh
lease). -
Only return
-EAGAINfrom the first (dentry-lease) walk when something
was actually freed. A full batch that frees n…
Source: NIST National Vulnerability Database NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-89647 has been found in Linux kernel.
Attackers can target a specific entry point like nr_to_scan over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 7.5/10.
What to do: apply the vendor's official patched release.
If unsure, ask your IT team or search "Linux kernel CVE-2026-89647" on the vendor's site.
CVE-2026-89647 (Linux kernel) — CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: nr_to_scan / expire_dir_lease / false / TOUCH
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (unclassified) exists in Linux kernel. Attackers reach the vulnerable code path via nr_to_scan without authentication.
Check the vendor advisory for the affected versions of Linux kernel. Attack surface: nr_to_scan / expire_dir_lease / false / TOUCH.
Severity: High (CVSS 7.5/10). Risk of unauthorized operations or information disclosure.
Update to the patched release per vendor advisory.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Audit SBOM/dependencies to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
Audit SBOM/dependencies for affected components.資産台帳・SBOM・依存マニフェストで Linux kernel を使っているサービスとバージョンを洗い出す。
-
2Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
References
- web git.kernel.org
- web git.kernel.org
- web git.kernel.org
- web git.kernel.org
- web nvd.nist.gov
- web github.com