Security readout for executives and security teams
Plain-English summary
CVE-2025-21879 is a high-severity Linux kernel Btrfs memory-safety flaw. A local low-privileged user may be able to trigger memory corruption with serious confidentiality, integrity, and availability impact. The supplied sources do not show active exploitation or CISA KEV listing.
Executive priority
Treat as high priority for Linux fleets with local users, shared hosting, developer workstations, or container platforms. It is not described as remotely exploitable in the supplied evidence, but kernel memory corruption can materially affect host security boundaries.
Technical view
In btrfs_scan_root(), the kernel could schedule an inode for delayed iput, then later dereference inode->root->fs_info via btrfs_fs_closing(). If the cleaner thread releases the inode first, this creates a use-after-free. The fix uses an already stored local fs_info pointer.
Likely exposure
Likely exposure is Linux systems running affected kernel versions, particularly 6.13 before fixed stable updates and 6.14 as listed. The bundle does not identify affected distributions, default Btrfs usage requirements, or package-level fixed versions.
Exploitation context
The CVSS vector is local, low complexity, low privilege, no user interaction, with high impact across confidentiality, integrity, and availability. KEV is false, and the provided sources contain no evidence of in-the-wild exploitation.
Researcher notes
Evidence supports a Btrfs kernel use-after-free caused by lifetime ordering around delayed iput and later inode field access. Public data is incomplete on exploitability prerequisites, affected distributions, and runtime configuration requirements, so validation should stay source- and vendor-advisory driven.
Mitigation direction
- Apply Linux kernel updates containing the referenced stable fixes.
- Check your Linux distribution advisory for fixed package versions.
- Prioritize systems allowing local shell, container, or multi-user access.
- Review Btrfs usage and exposure on affected kernel fleets.
- If no vendor package exists, follow vendor kernel mitigation guidance.
Validation and detection
- Inventory kernel versions across Linux hosts.
- Identify systems using or loading Btrfs functionality.
- Compare installed kernels with vendor fixed-version advisories.
- Confirm remediation includes the referenced stable commit lineage.
- Track CVE-2025-21879 for distro-specific backport status.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
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.
CWE-416: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2025-21879 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- High
- CVSS
- 7.8 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
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.
SSVC decision data
CVSS vector scores
1 official scoreWe 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.
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H1.85.9CISA-ADPVulnerability scoring details
Base CVSS 3.1 score
7.8HighVector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- CVE reservedCVE Program
The CVE ID was reserved by the assigning CNA.
- CVE publishedCVE Program
The CVE record was published.
- CVE updatedCVE Program
The CVE record metadata indicates this as the latest update time.
ADP provider summaries
Source materials
- CVE List V5 sourceCVE List V5
- https://git.kernel.org/stable/c/07836bc18f4ae42da4e922244f4685561c18755eCVE reference, Linux
- https://git.kernel.org/stable/c/5e79d26014f9386387575b9ed60d342057cee49bCVE reference, Linux
- https://git.kernel.org/stable/c/59f37036bb7ab3d554c24abc856aabca01126414CVE reference, Linux
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Use After Free
Use After Free represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.