Security readout for executives and security teams
Plain-English summary
A flaw in the Linux kernel’s optional dm-flakey data-corruption testing feature can corrupt kernel memory because a bio structure is initialized with the wrong parameter. A local, low-privileged attacker may be able to cause severe confidentiality, integrity, or availability impact. Exposure depends on the affected kernel code and feature being present and reachable.
Executive priority
Prioritize remediation for multi-user, shared, or otherwise locally accessible Linux systems. Treat this as a high-severity kernel update, but validate actual exposure because the vulnerable path belongs to an optional dm-flakey feature and the supplied affected-version representation is ambiguous. There is no supplied evidence of active exploitation.
Technical view
CVE-2025-21966 is a CWE-787 out-of-bounds write in dm-flakey’s optional corrupt_bio_byte functionality. The supplied CVSS 3.1 score is 7.8: local access, low complexity, low privileges, no user interaction, and high impact across confidentiality, integrity, and availability. Stable-kernel commits correct the parameter passed to bio_init.
Likely exposure
Systems running affected Linux kernels require review, especially where dm-flakey and corrupt_bio_byte are used or reachable. The supplied version data names 6.5, 6.6.84, 6.12.20, 6.13.8, and 6.14, but its range semantics are incomplete. Confirm exposure through distribution-specific advisories and patch provenance.
Exploitation context
The CVSS vector describes local, low-privileged exploitation with low complexity and no user interaction. The bundle marks this CVE as absent from KEV and provides no evidence of active exploitation or public weaponization. Whether practical exploitation requires additional dm-flakey configuration is not established by the supplied evidence.
Researcher notes
The defect is attributed specifically to an incorrect bio_init parameter in corrupt_bio_byte, producing kernel memory corruption. Four stable-tree fixes are cited, likely corresponding to maintained kernel branches. The bundle does not establish exploit reliability, required device-mapper permissions, feature defaults, or precise version ranges; those points should not be inferred without vendor or upstream confirmation.
Mitigation direction
- Upgrade to a vendor-supported kernel containing the applicable cited stable fix.
- Check distribution security guidance for exact affected and corrected package versions.
- Limit untrusted local access while affected systems await remediation.
- Review dm-flakey and corrupt_bio_byte usage before considering operational workarounds.
Validation and detection
- Record each system’s running kernel release and distribution package revision.
- Determine whether dm-flakey and corrupt_bio_byte are used in affected environments.
- Verify the installed kernel incorporates the applicable cited stable commit.
- Regression-test storage and device-mapper workloads after applying the corrected kernel.
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-787: 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-2025-21966 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
2 official scoresWe 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:H1.85.9LinuxCVSS: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
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/818330f756f3800c37d738bd36bce60eac949938CVE reference, Linux
- https://git.kernel.org/stable/c/5a87e46da2418c57b445371f5ca0958d5779ba5fCVE reference, Linux
- https://git.kernel.org/stable/c/da070843e153471be4297a12fdaa64023276f40eCVE reference, Linux
- https://git.kernel.org/stable/c/57e9417f69839cb10f7ffca684c38acd28ceb57bCVE 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.