Security readout for executives and security teams
Plain-English summary
CVE-2025-21962 is a Linux kernel CIFS issue where a local user-provided closetimeo mount option can overflow before validation. The documented impact is availability only, not data theft or tampering. Business urgency is highest where users or services can mount SMB/CIFS shares or influence CIFS mount options.
Executive priority
Treat this as a moderate operational risk. Patch through normal kernel maintenance, but accelerate on multi-user Linux systems, file servers, CI runners, container hosts, and environments where untrusted users can influence CIFS mounts.
Technical view
The flaw is an integer overflow in CIFS mount option processing. A u32 closetimeo value is converted from seconds to jiffies before the intended upper-limit check. CVSS 3.1 is 5.5: local attack vector, low complexity, low privileges, no user interaction, high availability impact.
Likely exposure
Exposure is most likely on Linux systems running affected kernels with CIFS support enabled and workflows that allow non-root users, containers, services, or automation to supply CIFS mount parameters. Exact exposure depends on distribution backports and whether vendor kernel packages include the referenced stable fixes.
Exploitation context
The source bundle does not cite active exploitation, and KEV is false. The vulnerability requires local privileges and control over a CIFS mount parameter. No public source in the bundle establishes remote exploitation or confidentiality/integrity impact.
Researcher notes
The core issue is CWE-190 in pre-validation conversion of closetimeo seconds to jiffies. Evidence supports local availability impact only. The bundle does not provide exploit telemetry, a named mitigation beyond kernel fixes, or a complete distribution-by-distribution affected matrix.
Mitigation direction
- Apply Linux kernel updates from your distribution or stable kernel provider.
- Review Debian LTS guidance if running affected Debian LTS kernels.
- Restrict who can mount CIFS shares or pass CIFS mount options.
- Check vendor advisories for fixed package versions and backports.
- Prioritize shared servers where untrusted local users can trigger mounts.
Validation and detection
- Inventory Linux kernel versions and distribution package revisions.
- Identify systems using CIFS or mounting SMB shares.
- Confirm installed kernels include the referenced stable fixes or vendor backports.
- Review mount policies for untrusted closetimeo parameter control.
- Verify monitoring covers local availability failures on CIFS hosts.
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-190: 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-2025-21962 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
- Medium
- CVSS
- 5.5 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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:N/I:N/A:H1.83.6CISA-ADPVulnerability scoring details
Base CVSS 3.1 score
5.5MediumVector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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/513f6cf2e906a504b7ab0b62b2eea993a6f64558CVE reference, Linux
- https://git.kernel.org/stable/c/9968fcf02cf6b0f78fbacf3f63e782162603855aCVE reference, Linux
- https://git.kernel.org/stable/c/6c13fcb7cf59ae65940da1dfea80144e42921e53CVE reference, Linux
- https://git.kernel.org/stable/c/1c46673be93dd2954f44fe370fb4f2b8e6214224CVE reference, Linux
- https://git.kernel.org/stable/c/b24edd5c191c2689c59d0509f0903f9487eb6317CVE reference, Linux
- https://git.kernel.org/stable/c/d5a30fddfe2f2e540f6c43b59cf701809995faefCVE reference, Linux
- https://lists.debian.org/debian-lts-announce/2025/05/msg00045.htmlCVE reference, CVE
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.
Integer Overflow or Wraparound
Integer Overflow or Wraparound represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.