High

CVE-2026-74321 — btrfs: fix invalid pointer dereference in __btrfs_run_delayed_refs()

In the Linux kernel, the following vulnerability has been resolved: btrfs: fix invalid pointer dereference in __btrfs_run_delayed_refs() In the beginning of the loop, we try to obtain a locked delayed ref head, if 'locked_ref' is currently NULL, by calling btrfs_select_ref_head(), which can return an error pointer. If the error pointer is -EAGAIN we do a continue and go back to the beginning of the loop, which will not try again to call btrfs_select_ref_head() since 'locked_ref' is no longer NULL but it's ERR_PTR(-EAGAIN), and then we do: spin_lock(&locked_ref->lock); against a ERR_PTR(-EAGAIN) value, generating an invalid pointer dereference. Fix this by ensuring that 'locked_ref' is set to NULL when btrfs_select_ref_head() returns ERR_PTR(-EAGAIN) and incrementing 'count' as well, to prevent infinite looping. We do this by doing a goto to the bottom of the loop that already sets 'locked_ref' to NULL and does a cond_resched(), with an increment to 'count' right before the goto. These measures were in place before the refactoring in commit 0110a4c43451 ("btrfs: refactor __btrfs_run_delayed_refs loop") but were unintentionally lost afterwards.

Published Aug 15, 2026 · Updated Oct 15, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: Linux

Low

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.

How the score was calculated

EPSS 0.7% (30-day exploitation probability)+8
Technical severity (high)+6

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation

Not confirmed

Not in CISA KEV — an absence of record, not proof it is unexploited.

EPSS FIRST

0.72%

ahead of 53% of scored CVEs · Oct 15, 2026

Affects

Linux

CVSS base

7.5

High · 2 source(s)

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

Identify exposed assets running the affected vendor/product/version combinations (Linux Linux).
The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
No fix documented in the sources: reduce exposure and monitor the vendor advisory.
Search available logs for exploit probes, errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

Vendor	Product	Versions	Status	Source
Linux	Linux	≥ 0110a4c43451533de1ea1bbdc57b5d452f9d8b25 and < c372ca227e16bace86f1df1fa4ae6849e2fcfa28≥ 0110a4c43451533de1ea1bbdc57b5d452f9d8b25 and < a71143590ce9764dbcb47617647592ff8b4d48bc≥ 0110a4c43451533de1ea1bbdc57b5d452f9d8b25 and < 65770111a2d47c2b15e20b2ba92bb12198f289d4≥ 0110a4c43451533de1ea1bbdc57b5d452f9d8b25 and < 015dc4a1e0c2cba551d4620eba13d26d5081dc34≥ 0110a4c43451533de1ea1bbdc57b5d452f9d8b25 and < ba9fa2ff5981589bb49094d3358c339b37c47f53≥ 0110a4c43451533de1ea1bbdc57b5d452f9d8b25 and < 3b15d02be05e74321adb1e0ae0cb4ccfba7c6cb1≥ 0110a4c43451533de1ea1bbdc57b5d452f9d8b25 and < 9faa6b69ad73f03c7bde53e07d75a28822dc9a1a≥ 0110a4c43451533de1ea1bbdc57b5d452f9d8b25 and < 486f8298b6188ff11ef1f4be7f1d5d2e4d1b1fae and 1 more version 4.20	Vulnerable	CVE Program (cve.org) e CISA ADP

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector

Network

Attack complexity

Low

Privileges required

None

User interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Scored by
7.5	CVSS 3.1	High	3.9	3.6	416baaa9-dc9f-4396-8d5f-8c081fb06d67 via NIST National Vulnerability Database
7.5	CVSS 3.1	High	—	—	Linux via CVE Program (cve.org) e CISA ADP

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H (score shown at the top: 416baaa9-dc9f-4396-8d5f-8c081fb06d67)

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).

web/proxy/WAF logsnetwork IDS/IPS

Timeline

What happened to this CVE, newest first.

2026
Affected products added · linux/linux
Oct 15, 2026 · CVE Program (cve.org) e CISA ADP
Record published
Oct 15, 2026
CVSS changed · 7.5
Oct 15, 2026 · NIST National Vulnerability Database
Source status changed · → Received
Oct 15, 2026 · NIST National Vulnerability Database
Record created in this database
Oct 15, 2026 · NIST National Vulnerability Database
CVE published
Aug 15, 2026 · Linux

Source activity

Repeated readings are counted rather than listed.

1× Official description updated · Oct 15, 2026 – Oct 15, 2026

References

8 on the record

git.kernel.org/stable/c/65770111a2d47c2b15e20b2ba92bb12198f289d4
NIST National Vulnerability Database
git.kernel.org/stable/c/486f8298b6188ff11ef1f4be7f1d5d2e4d1b1fae
NIST National Vulnerability Database
git.kernel.org/stable/c/3b15d02be05e74321adb1e0ae0cb4ccfba7c6cb1
NIST National Vulnerability Database
git.kernel.org/stable/c/ba9fa2ff5981589bb49094d3358c339b37c47f53
NIST National Vulnerability Database
git.kernel.org/stable/c/c372ca227e16bace86f1df1fa4ae6849e2fcfa28
NIST National Vulnerability Database
git.kernel.org/stable/c/9faa6b69ad73f03c7bde53e07d75a28822dc9a1a
NIST National Vulnerability Database
git.kernel.org/stable/c/015dc4a1e0c2cba551d4620eba13d26d5081dc34
NIST National Vulnerability Database
git.kernel.org/stable/c/a71143590ce9764dbcb47617647592ff8b4d48bc
NIST National Vulnerability Database

Elsewhere on this site

Linux
every CVE for this vendor

Related CVEs (same products)

Critical CVE-2026-99999 ipv4: validate checksum_start before completing checksum 22h
Unknown CVE-2026-98432 ipv4: free inet_opt and ireq_opt after an RCU grace period 22h
Unknown CVE-2026-98424 wifi: cfg80211: undo netns switch if renaming the wiphy fails 1d
Unknown CVE-2026-98425 wifi: mac80211: don't warn when an IBSS has no channel to scan 1d
Unknown CVE-2026-98426 wifi: mwifiex: fix IRQ leak using wrong index in MSI-X error path 1d
Unknown CVE-2026-98427 net/sched: codel: bound the dropping loop per dequeue call 1d

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No fixed version, patch or mitigation documented.
No CISA SSVC assessment.
No CWE classification.
No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-74321 is "btrfs: fix invalid pointer dereference in __btrfs_run_delayed_refs()", rated High. It affects Linux (Linux); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 7.5 describes technical severity. EPSS 0.72% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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