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CVE Record

CVE-2025-21736: nilfs2: fix possible int overflows in nilfs_fiemap()

In the Linux kernel, the following vulnerability has been resolved: nilfs2: fix possible int overflows in nilfs_fiemap() Since nilfs_bmap_lookup_contig() in nilfs_fiemap() calculates its result by being prepared to go through potentially maxblocks == INT_MAX blocks, the value in n may experience an overflow caused by left shift of blkbits. While it is extremely unlikely to occur, play it safe and cast right hand expression to wider type to mitigate the issue. Found by Linux Verification Center (linuxtesting.org) with static analysis tool SVACE.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

CVE-2025-21736 is a Linux kernel NILFS2 filesystem bug involving a possible integer overflow. The kernel description says the condition is extremely unlikely, and the bundle provides no CVSS score or confirmed exploitation. Treat it as routine kernel maintenance unless your environment uses NILFS2 or tracks Linux kernel fixes tightly.

Executive priority

Handle through normal kernel patch governance. Escalate only for systems using NILFS2, exposed multi-user Linux platforms, or environments with strict kernel compliance requirements. Current evidence does not support emergency response language.

Technical view

The issue is in nilfs_fiemap(), where nilfs_bmap_lookup_contig() may process up to INT_MAX blocks. A left shift using blkbits could overflow n, so stable kernel patches cast the expression to a wider type. The bug was found by Linux Verification Center using SVACE static analysis.

Likely exposure

Exposure is most relevant to Linux systems running affected kernel versions with NILFS2 filesystem functionality present or used. The source bundle lists affected Linux versions and multiple stable kernel fix commits, but does not identify specific downstream package versions beyond Debian LTS advisories.

Exploitation context

The bundle does not report active exploitation, public exploit availability, or KEV listing. The kernel description says the condition is extremely unlikely. Impact details are incomplete, so exploitation practicality and security consequence should not be overstated.

Researcher notes

Key uncertainty is impact. Sources describe a possible integer overflow and a conservative type-widening fix, but provide no CVSS, CWE, exploit status, or demonstrated attack path. Validation should focus on kernel branch provenance and downstream vendor backports.

Mitigation direction

  • Apply Linux stable or distribution kernel updates that include the NILFS2 fiemap fix.
  • Review Debian LTS advisories if managing Debian-based long-term support systems.
  • Check vendor security guidance for exact fixed package versions.
  • Prioritize hosts that use or mount NILFS2 filesystems.
  • Avoid direct wrangler or deployment assumptions; this is kernel patch management only.

Validation and detection

  • Inventory running Linux kernel versions across affected assets.
  • Check whether NILFS2 filesystems are mounted or required.
  • Confirm patched kernels include the referenced stable fix commit for the branch.
  • Verify Debian systems against the cited Debian LTS advisories.
  • Document exceptions where vendor-fixed packages are not yet available.
Prepared
Confidence
medium
Sources
12

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.

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CVE-2025-21736 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
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.

0CVSS vectors
3Timeline events
1ADP providers
11Source links

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
LinuxLinux622daaff0a8975fb5c5b95f24f3234550ba32e92, 622daaff0a8975fb5c5b95f24f3234550ba32e92, 622daaff0a8975fb5c5b95f24f3234550ba32e92, 622daaff0a8975fb5c5b95f24f3234550ba32e92, 622daaff0a8975fb5c5b95f24f3234550ba32e92, 622daaff0a8975fb5c5b95f24f3234550ba32e92, 622daaff0a8975fb5c5b95f24f3234550ba32e92, 622daaff0a8975fb5c5b95f24f3234550ba32e92unaffected
LinuxLinux2.6.38, 0, 5.4.291, 5.10.235, 5.15.179, 6.1.129, 6.6.78, 6.12.14, 6.13.3, 6.14affected
Weakness

CWE details

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