LiveActive security incident?Get immediate response
CVE Record

CVE-2025-71159: btrfs: fix use-after-free warning in btrfs_get_or_create_delayed_node()

In the Linux kernel, the following vulnerability has been resolved: btrfs: fix use-after-free warning in btrfs_get_or_create_delayed_node() Previously, btrfs_get_or_create_delayed_node() set the delayed_node's refcount before acquiring the root->delayed_nodes lock. Commit e8513c012de7 ("btrfs: implement ref_tracker for delayed_nodes") moved refcount_set inside the critical section, which means there is no longer a memory barrier between setting the refcount and setting btrfs_inode->delayed_node. Without that barrier, the stores to node->refs and btrfs_inode->delayed_node may become visible out of order. Another thread can then read btrfs_inode->delayed_node and attempt to increment a refcount that hasn't been set yet, leading to a refcounting bug and a use-after-free warning. The fix is to move refcount_set back to where it was to take advantage of the implicit memory barrier provided by lock acquisition. Because the allocations now happen outside of the lock's critical section, they can use GFP_NOFS instead of GFP_ATOMIC.

CriticalCVSS 9.8Not KEV-listedUpdated
Discuss exposureBack to CVEs
Glexia's TakeAutomated analysiscritical

Security readout for executives and security teams

Plain-English summary

A Linux Btrfs concurrency flaw can expose already-freed kernel memory when two threads observe initialization in different orders. Affected systems may experience kernel instability and potentially broader security impact. The supplied rating is critical, but the sources do not demonstrate remote reachability or successful exploitation.

Executive priority

Treat as an urgent kernel maintenance issue on Btrfs-enabled systems, especially shared or exposed infrastructure. Validate actual exposure before assuming the network-scored worst case. Expedite vendor-fixed kernels, while recognizing that the provided evidence does not establish active exploitation.

Technical view

A missing ordering barrier in btrfs_get_or_create_delayed_node() can expose btrfs_inode->delayed_node before node->refs is initialized. Another thread may increment an unset reference count, causing faulty lifetime management and a use-after-free warning. The correction restores refcount_set before lock acquisition, using the lock’s implicit memory barrier.

Likely exposure

Exposure is limited to Linux systems running the listed affected kernel versions and using Btrfs code paths. The bundle identifies versions around 6.18 through 6.19, but its version data is ambiguous and should be confirmed against distribution advisories and kernel commit ancestry.

Exploitation context

The supplied CVSS is 9.8 with a network attack vector. However, the technical sources describe an internal Btrfs race and do not explain a remotely reachable trigger. The CVE is not listed as KEV in the bundle, and no cited source reports active exploitation or a public exploit.

Researcher notes

The central condition is a store-ordering race introduced after refcount initialization moved inside root->delayed_nodes locking. The fix restores initialization ordering and permits GFP_NOFS allocations outside the critical section. Precise vulnerable release boundaries, trigger reliability, and security impact beyond the warning are not fully established by the supplied sources.

Mitigation direction

  • Install a vendor-supported kernel containing one of the referenced stable fixes.
  • Check distribution advisories for exact fixed package versions and reboot requirements.
  • Prioritize hosts using Btrfs or processing storage activity from less-trusted workloads.
  • Use vendor-recommended operational mitigations if immediate kernel replacement is unavailable.

Validation and detection

  • Record running kernel versions and identify systems with mounted Btrfs filesystems.
  • Compare kernel packages and commit ancestry with the referenced stable fixes.
  • Confirm updated systems booted into the fixed kernel, not an older installed kernel.
  • Review kernel logs for Btrfs refcount, use-after-free, or related memory-safety warnings.
Prepared
Confidence
medium
Sources
4

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cve · low confidence lookup

CVE-2025-71159 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

Open ATT&CK lookup
Vulnerability profileCVE Program record
Severity
Critical
CVSS
9.8 (3.1)
Known Exploited
No
Published

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

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

1CVSS vectors
3Timeline events
0ADP providers
3Source links

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
9.8CVSS 3.1CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H3.95.9Linux

Vulnerability scoring details

Base CVSS 3.1 score

9.8Critical
CVSS 3.1 vector shape for CVE-2025-71159Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

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

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinuxe8513c012de75fd65e2df5499572bc6ef3f6e409, e8513c012de75fd65e2df5499572bc6ef3f6e409unaffected
LinuxLinux6.18, 0, 6.18.6, 6.19affected
Weakness

CWE details

No CWE listed

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.