VulnerabilityPublished 17 Sep 2026Updated 30 Oct 2026

CVE-2026-90263: Linux kernel · btrfs: check if root is readonly when setting posix acl

Source GCVE Database

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Authoritative record:CVE-2026-90263· Medium

Not known to be exploited · fixed in f3e6b504a79d8e90bb7aa8a03a42dc2b51dcc4c4 : update Linux kernel when convenient.

Data as of 30 Oct 2026, 18:33 UTC

Severity

Medium

Rated Medium by Threat Radar's AI analysis · CVSS not yet scored by NVD

Thin evidence

One scorer or none

Patch: Available – fixed in f3e6b504a79d8e90bb7aa8a03a42dc2b51dcc4c4, dc3a6e90a0a6350a6d43fed9f005f54171809580, d5602f96ff1e266f069b4d0d94f441050e057e06 +3

Exploitation evidence

Disclosed: evidence found.
CVE published 17 Sep 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: 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 30 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.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), 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-wxw8-hpqh-3xg2

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected ≥ 353c2ea735e4b54fb6250861e67b51b1bcb47198, < f3e6b504a79d8e90bb7aa8a03a42dc2b51dcc4c4	Fixed in f3e6b504a79d8e90bb7aa8a03a42dc2b51dcc4c4
LinuxLinux	Affected ≥ 353c2ea735e4b54fb6250861e67b51b1bcb47198, < dc3a6e90a0a6350a6d43fed9f005f54171809580	Fixed in dc3a6e90a0a6350a6d43fed9f005f54171809580
LinuxLinux	Affected ≥ 353c2ea735e4b54fb6250861e67b51b1bcb47198, < d5602f96ff1e266f069b4d0d94f441050e057e06	Fixed in d5602f96ff1e266f069b4d0d94f441050e057e06
LinuxLinux	Affected ≥ 353c2ea735e4b54fb6250861e67b51b1bcb47198, < ce8103676f4d4b13e1f087fcfb34f80774d30be2	Fixed in ce8103676f4d4b13e1f087fcfb34f80774d30be2
LinuxLinux	Affected ≥ 353c2ea735e4b54fb6250861e67b51b1bcb47198, < 20b2c2f3316e82a76ae3358c0bd45824f50f3fd5	Fixed in 20b2c2f3316e82a76ae3358c0bd45824f50f3fd5
LinuxLinux	Affected ≥ 353c2ea735e4b54fb6250861e67b51b1bcb47198, < 01c2f41fc441f75b3f9326443372faceb1cb6638	Fixed in 01c2f41fc441f75b3f9326443372faceb1cb6638

AI-suggested

A fix has been implemented in the Linux kernel to ensure the root's read-only status is checked before setting POSIX ACLs on btrfs filesystems. Users should update to a kernel version that includes this fix once available. Until then, no other specific mitigations are indicated.

Description

A vulnerability in the Linux kernel's btrfs filesystem allowed setting POSIX ACLs even when the filesystem root was marked as read-only. This occurred because the set_acl code path did not verify the read-only status of the root, unlike other write operations which were properly denied. The issue was introduced by a commit that removed a redundant read-only check without ensuring all callers performed this verification. The vulnerability has been resolved by reinstating the read-only check before setting ACLs.

Impact

This vulnerability could allow unauthorized modification of POSIX ACLs on a btrfs filesystem that is intended to be read-only, potentially leading to unauthorized changes in access control permissions. However, no other write operations are affected. There is no indication of active exploitation in the wild.

Summary

The Linux kernel's btrfs filesystem had a flaw where the set_acl operation did not check if the root was read-only, allowing ACL modifications despite the filesystem being marked read-only. This was due to a commit that removed a redundant read-only check in btrfs_setxattr_trans without confirming that all callers enforced this check. The vulnerability was fixed by ensuring the root's read-only flag is always checked before performing set_acl operations, preventing unauthorized write operations on read-only filesystems.

References

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