VulnerabilityPublished 23 Oct 2026

CVE-2026-99084: Linux kernel · readdir: take no inode lock on an immutable directory

Source GCVE Database

Authoritative record:CVE-2026-99084· Medium

Not known to be exploited : upgrade to e08f57a7dcb83818c058e415988c23beb6c5a47f or 6d30b399ae28e5166d62484f81ccaefde6fe7996 when convenient.

Data as of 26 Oct 2026, 12:55 UTC

Severity

Medium

Rated by Threat Radar · CVSS not yet scored by NVD

EPSS: 0.1% chance of exploitation in 30 days – higher than 3% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in e08f57a7dcb83818c058e415988c23beb6c5a47f, 6d30b399ae28e5166d62484f81ccaefde6fe7996

Exploitation evidence

Disclosed: evidence found.
CVE published 23 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

ghsa-p3rf-jfv8-g4c7

What to do

Upgrade Linux kernel to e08f57a7dcb83818c058e415988c23beb6c5a47f or 6d30b399ae28e5166d62484f81ccaefde6fe7996.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected ≥ 9d4e752a24f740b31ca827bfab07010e4e7f34b0, < e08f57a7dcb83818c058e415988c23beb6c5a47f	Fixed in e08f57a7dcb83818c058e415988c23beb6c5a47f
LinuxLinux	Affected ≥ 9d4e752a24f740b31ca827bfab07010e4e7f34b0, < 6d30b399ae28e5166d62484f81ccaefde6fe7996	Fixed in 6d30b399ae28e5166d62484f81ccaefde6fe7996
LinuxLinux	Affected =7.1	Fixed in–

AI-suggested

A fix has been implemented in the Linux kernel to address this issue by adding the FOP_IMMUTABLE flag and modifying iterate_dir() to skip inode locking on immutable directories. Users should apply the official kernel update containing this fix once available. Patch status is not explicitly confirmed in the provided data; therefore, check the vendor or kernel advisory for the current remediation guidance and apply updates accordingly.

Description

A vulnerability in the Linux kernel's readdir implementation related to inode locking on immutable directories has been resolved. The issue involved iterate_dir() holding a shared lock on the directory's i_rwsem semaphore even when the directory was immutable and never changed, causing unnecessary blocking. This could lead to stalls in mount namespaces sharing the same nullfs directory inode, impacting multiple users. The fix adds a FOP_IMMUTABLE flag to skip locking for directories that never change or are never removed, preventing the described contention.

Impact

The vulnerability could cause system stalls or delays in mount namespaces sharing the same immutable directory inode, affecting kernel threads and users relying on these namespaces. While it does not directly lead to privilege escalation or data corruption, the blocking behavior can degrade system responsiveness and impact workloads relying on mount namespaces. No known exploits in the wild have been reported.

Summary

The Linux kernel vulnerability CVE-2026-99084 concerns the readdir function's inode locking behavior on immutable directories. Specifically, iterate_dir() took a shared i_rwsem lock on directories that never have entries and are never removed, such as nullfs directories used as roots of empty mount namespaces. This lock ordering caused readers and writers to block each other unnecessarily, potentially stalling all users sharing the inode. The fix introduces the FOP_IMMUTABLE flag for directories that never change, allowing iterate_dir() to skip taking the inode lock, thus eliminating the blocking issue. The flag is set on nullfs directories, and the patch ensures that other directory operations do not interfere with this behavior.

References

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