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NVD / CVE Program· CNA Linux

CVE-2026-72170: 9p: skip nlink update in cacheless mode to fix WARN_ON

Noroxi assessment

Priority: Monitor (action score 31/100)

  • 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: 0.16% (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 4ec4ebe40c82cb4c60756732f6593055d010c59c, 574aa0b4799470ac814479f1138d19efe6262255, 6086469f7d469549bfd070348b717a6e43736200.

Low priority for now. Upgrade to Linux Linux 4ec4ebe40c82cb4c60756732f6593055d010c59c, 574aa0b4799470ac814479f1138d19efe6262255, 6086469f7d469549bfd070348b717a6e43736200 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: 9p: skip nlink update in cacheless mode to fix WARN_ON v9fs_dec_count() unconditionally calls drop_nlink() on regular files, even when the inode's nlink is already zero. In cacheless mode the client refetches inode metadata from the server (the source of truth) on every operation, so by the time v9fs_remove() returns, the locally cached nlink may already reflect the post-unlink value: 1. Client initiates unlink, server processes it and sets nlink to 0 2. Client refetches inode metadata (nlink=0) before unlink returns 3. Client's v9fs_remove() completes successfully 4. Client calls v9fs_dec_count() which calls drop_nlink() on nlink=0 This race is easily triggered under heavy unlink workloads, such as stress-ng's unlink stressor, producing the following warning: WARNING: fs/inode.c:417 at drop_nlink+0x4c/0xc8 Call trace: drop_nlink+0x4c/0xc8 v9fs_remove+0x1e0/0x250 [9p] v9fs_vfs_unlink+0x20/0x38 [9p] vfs_unlink+0x13c/0x258 ... In cacheless mode the server is authoritative and the inode is on its way out, so locally adjusting nlink buys nothing. Skip v9fs_dec_count() entirely when neither CACHE_META nor CACHE_LOOSE is set, which both avoids the warning and removes a class of nlink races (two concurrent unlinkers observing nlink > 0 and both calling drop_nlink()) that an nlink == 0 guard alone would only narrow rather than close.

HighCVSS 7.8 · v3.1—No exploit Fix available
Published
Aug 15, 2026
Updated
Oct 16, 2026
EPSS
0.1% · 6th percentile
CWE
—

Report tools

JSON

Action score

31

Monitor

Low priority for now.

CVSS
31 / 40 · 7.8 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.1%

CISA SSVC decision

Exploitation
none
Automatable
no
Technical impact
total

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
—
CNA · Linux
7.8
NVD has not scored this yet; the score shown is the CNA’s.

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

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  • No public exploit code on record
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Noroxi analysis

What does it mean in your environment?

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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.

—

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

    • 4.17affected
    • ac89b2ef9b55924bcf922251f043ba73a32d05bb and later · before 6086469f7d469549bfd070348b717a6e43736200affected · git
    • ac89b2ef9b55924bcf922251f043ba73a32d05bb and later · before ab257019cb72f467b55c95384d99c94e3908b928affected · git
    • ac89b2ef9b55924bcf922251f043ba73a32d05bb and later · before 4ec4ebe40c82cb4c60756732f6593055d010c59caffected · git
    • ac89b2ef9b55924bcf922251f043ba73a32d05bb and later · before a5a682b016ef5b5384e28f6d652d47a8f8e73d37affected · git
    • ac89b2ef9b55924bcf922251f043ba73a32d05bb and later · before de79c3f3643841b8659a71958df7cf2a66bfd409affected · git
    • ac89b2ef9b55924bcf922251f043ba73a32d05bb and later · before 8d610017c992de705b304d3d727a6e3a86af6149affected · git
    • ac89b2ef9b55924bcf922251f043ba73a32d05bb and later · before 8faccac11e1369adddf5d80f4a45af93f13b2e1aaffected · git
    • ac89b2ef9b55924bcf922251f043ba73a32d05bb and later · before 574aa0b4799470ac814479f1138d19efe6262255affected · git
    • before 4.17not affected · semver

Package-level exposure

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

EcosystemPackageAffected rangeFix
Debian:12linuxbefore 6.1.187-16.1.187-1
Debian:13linuxbefore 6.12.100-16.12.100-1
Debian:14linuxbefore 7.1.5-17.1.5-1

Same product

linux: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-74705udp: fix potential use-after-free in tunnel segmentation
    40Plan
  • CVE-2026-74612veth: fix skb length accounting after XDP frag adjustment
    40Plan
  • CVE-2026-74475vxlan: use neigh_ha_snapshot() in route_shortcircuit()
    40Plan

Published before and after this one in the same product

  • ← EarlierCVE-2026-72165Aug 15, 2026 · mtd: rawnand: fix condition in 'nand_select_target()'
    31Monitor
  • ← EarlierCVE-2026-72168Aug 15, 2026 · mtd: maps: vmu-flash: fix fault in unaligned fixup
    0Monitor
  • Later →CVE-2026-72172Aug 15, 2026 · mm/mm_init: fix uninitialized struct pages for ZONE_DEVICE
    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 / packageFixed versionSource
Linux Linux4ec4ebe40c82cb4c60756732f6593055d010c59cVendor (CNA)
Linux Linux574aa0b4799470ac814479f1138d19efe6262255Vendor (CNA)
Linux Linux6086469f7d469549bfd070348b717a6e43736200Vendor (CNA)
Linux Linux8d610017c992de705b304d3d727a6e3a86af6149Vendor (CNA)
Linux Linux8faccac11e1369adddf5d80f4a45af93f13b2e1aVendor (CNA)
Linux Linuxa5a682b016ef5b5384e28f6d652d47a8f8e73d37Vendor (CNA)
Linux Linuxab257019cb72f467b55c95384d99c94e3908b928Vendor (CNA)
Linux Linuxde79c3f3643841b8659a71958df7cf2a66bfd409Vendor (CNA)
debian:linux6.1.187-1 · Debian:12Package 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.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

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).

Technical details

Attack conditions

  • 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.

If successful

Confidentiality
high · data can be read
Integrity
high · data or configuration can be modified
Availability
high · the service can be disrupted
Attack vector
Local
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality impact
High
Integrity impact
High
Availability impact
High

Weakness class (CWE)

—

CVSS vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

nvd-secondary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Change log

  1. SSVC exploitation— → none
  2. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (7 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records