# CVE-2026-45912: ext4: don't cache extent during splitting extent

Status: published. Published: 2026-05-27. Updated: 2026-11-06.

In the Linux kernel, the following vulnerability has been resolved:

ext4: don't cache extent during splitting extent

Caching extents during the splitting process is risky, as it may result
in stale extents remaining in the status tree. Moreover, in most cases,
the corresponding extent block entries are likely already cached before
the split happens, making caching here not particularly useful.

Assume we have an unwritten extent, and then DIO writes the first half.

  [UUUUUUUUUUUUUUUU] on-disk extent        U: unwritten extent
  [UUUUUUUUUUUUUUUU] extent status tree
  |<-   ->| ----> dio write this range

First, when ext4_split_extent_at() splits this extent, it truncates the
existing extent and then inserts a new one. During this process, this
extent status entry may be shrunk, and calls to ext4_find_extent() and
ext4_cache_extents() may occur, which could potentially insert the
truncated range as a hole into the extent status tree. After the split
is completed, this hole is not replaced with the correct status.

  [UUUUUUU|UUUUUUUU] on-disk extent        U: unwritten extent
  [UUUUUUU|HHHHHHHH] extent status tree    H: hole

Then, the outer calling functions will not correct this remaining hole
extent either. Finally, if we perform a delayed buffer write on this
latter part, it will re-insert the delayed extent and cause an error in
space accounting.

In adition, if the unwritten extent cache is not shrunk during the
splitting, ext4_cache_extents() also conflicts with existing extents
when caching extents. In the future, we will add checks when caching
extents, which will trigger a warning. Therefore, Do not cache extents
that are being split.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- Linux / Linux: ≥ 107a7bd31ac003e42c0f966aa8e5b26947de6024; < 8302b5b4aacdbb378f7b1216bb2ee782b5142415 (affected, git); ≥ 107a7bd31ac003e42c0f966aa8e5b26947de6024; < 692103feca376ae4298c92aa8828015d20f1d87b (affected, git); ≥ 107a7bd31ac003e42c0f966aa8e5b26947de6024; < 4c2d9dac4d328244f9365b0a1fa27ec802821820 (affected, git); ≥ 107a7bd31ac003e42c0f966aa8e5b26947de6024; < 93b2ebbbcb2e63cfc21a1946dfe91d3aa7952036 (affected, git); ≥ 107a7bd31ac003e42c0f966aa8e5b26947de6024; < 96007fd3c106aea773c1afae2d6f64cceb6da208 (affected, git); ≥ 107a7bd31ac003e42c0f966aa8e5b26947de6024; < 5b1f4290453314e11cd8e15c7baa8a9b76c19b23 (affected, git); ≥ 107a7bd31ac003e42c0f966aa8e5b26947de6024; < 9a2b95cdaf07785e2739199037bd9c0863ccc1be (affected, git); ≥ 107a7bd31ac003e42c0f966aa8e5b26947de6024; < 8b4b19a2f96348d70bfa306ef7d4a13b0bcbea79 (affected, git). Source: CNA: Linux
- Linux / Linux: 3.12 (affected); ≥ 0; < 3.12 (unaffected, semver); ≥ 5.10.252; ≤ 5.10.* (unaffected, semver); ≥ 5.15.202; ≤ 5.15.* (unaffected, semver); ≥ 6.1.165; ≤ 6.1.* (unaffected, semver); ≥ 6.6.128; ≤ 6.6.* (unaffected, semver); ≥ 6.12.75; ≤ 6.12.* (unaffected, semver); ≥ 6.18.14; ≤ 6.18.* (unaffected, semver); ≥ 6.19.4; ≤ 6.19.* (unaffected, semver); ≥ 7.0; ≤ * (unaffected, original_commit_for_fix). Source: CNA: Linux

## Severity and prioritization

- CISA KEV: No listing in collected sources

- EPSS: 0.12% as of 2026-11-06; percentile 2.09%

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: Not reported

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://git.kernel.org/stable/c/8302b5b4aacdbb378f7b1216bb2ee782b5142415 (CNA: Linux)

- https://git.kernel.org/stable/c/692103feca376ae4298c92aa8828015d20f1d87b (CNA: Linux)

- https://git.kernel.org/stable/c/4c2d9dac4d328244f9365b0a1fa27ec802821820 (CNA: Linux)

- https://git.kernel.org/stable/c/93b2ebbbcb2e63cfc21a1946dfe91d3aa7952036 (CNA: Linux)

- https://git.kernel.org/stable/c/96007fd3c106aea773c1afae2d6f64cceb6da208 (CNA: Linux)

- https://git.kernel.org/stable/c/5b1f4290453314e11cd8e15c7baa8a9b76c19b23 (CNA: Linux)

- https://git.kernel.org/stable/c/9a2b95cdaf07785e2739199037bd9c0863ccc1be (CNA: Linux)

- https://git.kernel.org/stable/c/8b4b19a2f96348d70bfa306ef7d4a13b0bcbea79 (CNA: Linux)

## Provenance

- CNA: Linux: https://www.cve.org/CVERecord?id=CVE-2026-45912; retrieved 2026-11-06; source updated 2026-11-06

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-45912; retrieved 2026-11-06; source updated Not reported

Revision: 692017a9f76119e899c90bc06595b9367f08f96a5814f48635dd7df7f7087812

Canonical: https://y2.dev/cve/CVE-2026-45912

## Agent and API access

Public CVE pages, Markdown, and JSON are free to read without an account or API key.

- Public catalog: https://y2.dev/cve/index.json. Follow nextCursor with the same search, filters, sort, and limit (1–100). A null cursor marks the end.

- WebMCP: search_cve_disclosures, get_cve_disclosure, get_cve_page_markdown, get_y2_cve_access. Available in compatible browsers.

- Cyber API: https://api.y2.dev/api/v2/cyber/cves and https://api.y2.dev/api/v2/cyber/cves/{cveId}.

- Y2 Pro or Elite: create a workspace API key with the intel:cyber scope and send Authorization: Bearer <Y2_API_KEY>. Setup: https://y2.dev/docs/api/create-key.

- x402: Pay per request without an account or API key. Omit Authorization, read the HTTP 402 PAYMENT-REQUIRED challenge, validate its current requirements, and retry with PAYMENT-SIGNATURE through an authorized payment client. These browser tools never make payments. Guide: https://y2.dev/docs/api/x402.

- OpenAPI: https://y2.dev/api/openapi.yaml. Agent access metadata: https://y2.dev/cve/agent.json.

Collected public records only. Check source status for coverage and freshness.