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CVE Record

CVE-2025-21646: afs: Fix the maximum cell name length

In the Linux kernel, the following vulnerability has been resolved: afs: Fix the maximum cell name length The kafs filesystem limits the maximum length of a cell to 256 bytes, but a problem occurs if someone actually does that: kafs tries to create a directory under /proc/net/afs/ with the name of the cell, but that fails with a warning: WARNING: CPU: 0 PID: 9 at fs/proc/generic.c:405 because procfs limits the maximum filename length to 255. However, the DNS limits the maximum lookup length and, by extension, the maximum cell name, to 255 less two (length count and trailing NUL). Fix this by limiting the maximum acceptable cellname length to 253. This also allows us to be sure we can create the "/afs/.<cell>/" mountpoint too. Further, split the YFS VL record cell name maximum to be the 256 allowed by the protocol and ignore the record retrieved by YFSVL.GetCellName if it exceeds 253.

HighCVSS 7.5Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

A Linux AFS naming-limit mismatch can trigger a kernel warning and disrupt availability when an excessively long AFS cell name is processed. The issue matters primarily to systems using the kernel’s AFS filesystem; ordinary Linux hosts without AFS exposure are less likely to be affected.

Executive priority

Treat this as a focused high-priority availability issue, not an enterprise-wide emergency. Promptly patch AFS-dependent or externally exposed systems, then handle other affected hosts through normal kernel maintenance. Escalate if monitoring finds related warnings or if critical services rely on AFS.

Technical view

Linux kafs accepted cell names up to 256 bytes, but procfs filenames allow only 255 and the applicable DNS-derived limit is 253. Processing an overlong name could fail while creating an AFS procfs entry and raise a kernel warning. The fix caps accepted cell names at 253 and ignores oversized YFS VL cell-name records.

Likely exposure

Potential exposure is limited to Linux systems running affected kernel builds with kernel AFS functionality in use or reachable through relevant AFS interactions. The supplied version data is ambiguous, so organizations should map installed distribution kernels to vendor advisories or confirmed backports rather than relying only on upstream version numbers.

Exploitation context

The supplied CVSS is 7.5, reflecting remotely reachable, low-complexity availability impact without privileges or user interaction. However, the bundle reports no CISA KEV listing and provides no evidence of active exploitation or a public exploit. Practical reachability depends on AFS configuration and how cell names are obtained.

Researcher notes

The core defect is inconsistent length validation across kafs, procfs, DNS-derived naming constraints, and YFS protocol records. The correction separates the protocol maximum from the locally acceptable 253-byte maximum. No CWE is supplied. Exact vulnerable ranges and exploitability conditions remain insufficiently detailed in the provided bundle.

Mitigation direction

  • Update to a vendor-supported kernel containing the upstream cell-name length fix.
  • Check distribution security guidance for backport status and the correct fixed package.
  • Prioritize systems actively using AFS or accepting AFS cell information from external sources.
  • If immediate updating is impossible, obtain vendor-approved temporary mitigation guidance.

Validation and detection

  • Inventory kernel versions and identify hosts where kernel AFS support is enabled or used.
  • Confirm the installed kernel includes the relevant upstream fix or distribution backport.
  • Review kernel logs for AFS-related procfs warnings involving unusually long cell names.
  • Verify oversized YFS VL cell-name records are rejected or ignored after remediation.
Prepared
Confidence
medium
Sources
6

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

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CVE-2025-21646 mapping review

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Vulnerability profileCVE Program record
Severity
High
CVSS
7.5 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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
1ADP providers
9Source 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
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6Linux

Vulnerability scoring details

Base CVSS 3.1 score

7.5High
CVSS 3.1 vector shape for CVE-2025-21646Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

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

ADP provider summaries

CVECVE Program Container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinuxc3e9f888263bb4df11cbd623ceced02081cb2f9f, c3e9f888263bb4df11cbd623ceced02081cb2f9f, c3e9f888263bb4df11cbd623ceced02081cb2f9f, c3e9f888263bb4df11cbd623ceced02081cb2f9f, c3e9f888263bb4df11cbd623ceced02081cb2f9f, c3e9f888263bb4df11cbd623ceced02081cb2f9funaffected
LinuxLinux5.8, 0, 5.10.234, 5.15.177, 6.1.125, 6.6.72, 6.12.10, 6.13affected
Weakness

CWE details

No CWE listed

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