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CVE Record

CVE-2025-23150: ext4: fix off-by-one error in do_split

In the Linux kernel, the following vulnerability has been resolved: ext4: fix off-by-one error in do_split Syzkaller detected a use-after-free issue in ext4_insert_dentry that was caused by out-of-bounds access due to incorrect splitting in do_split. BUG: KASAN: use-after-free in ext4_insert_dentry+0x36a/0x6d0 fs/ext4/namei.c:2109 Write of size 251 at addr ffff888074572f14 by task syz-executor335/5847 CPU: 0 UID: 0 PID: 5847 Comm: syz-executor335 Not tainted 6.12.0-rc6-syzkaller-00318-ga9cda7c0ffed #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/30/2024 Call Trace: <TASK> __dump_stack lib/dump_stack.c:94 [inline] dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120 print_address_description mm/kasan/report.c:377 [inline] print_report+0x169/0x550 mm/kasan/report.c:488 kasan_report+0x143/0x180 mm/kasan/report.c:601 kasan_check_range+0x282/0x290 mm/kasan/generic.c:189 __asan_memcpy+0x40/0x70 mm/kasan/shadow.c:106 ext4_insert_dentry+0x36a/0x6d0 fs/ext4/namei.c:2109 add_dirent_to_buf+0x3d9/0x750 fs/ext4/namei.c:2154 make_indexed_dir+0xf98/0x1600 fs/ext4/namei.c:2351 ext4_add_entry+0x222a/0x25d0 fs/ext4/namei.c:2455 ext4_add_nondir+0x8d/0x290 fs/ext4/namei.c:2796 ext4_symlink+0x920/0xb50 fs/ext4/namei.c:3431 vfs_symlink+0x137/0x2e0 fs/namei.c:4615 do_symlinkat+0x222/0x3a0 fs/namei.c:4641 __do_sys_symlink fs/namei.c:4662 [inline] __se_sys_symlink fs/namei.c:4660 [inline] __x64_sys_symlink+0x7a/0x90 fs/namei.c:4660 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f </TASK> The following loop is located right above 'if' statement. for (i = count-1; i >= 0; i--) { /* is more than half of this entry in 2nd half of the block? */ if (size + map[i].size/2 > blocksize/2) break; size += map[i].size; move++; } 'i' in this case could go down to -1, in which case sum of active entries wouldn't exceed half the block size, but previous behaviour would also do split in half if sum would exceed at the very last block, which in case of having too many long name files in a single block could lead to out-of-bounds access and following use-after-free. Found by Linux Verification Center (linuxtesting.org) with Syzkaller.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

CVE-2025-23150 is a Linux kernel ext4 filesystem bug. A directory-splitting error can cause out-of-bounds memory access and a use-after-free during directory entry insertion. The public record does not show active exploitation or a CVSS score, so urgency should be driven by kernel exposure and vendor patch availability.

Executive priority

Treat this as a kernel maintenance priority, not an emergency based on current evidence. Patch exposed Linux fleets through normal accelerated kernel update processes, especially shared, multi-tenant, or untrusted-workload environments.

Technical view

The flaw is an off-by-one error in ext4 do_split. Syzkaller found that incorrect htree directory splitting can lead ext4_insert_dentry to write out of bounds, triggering KASAN use-after-free during symlink creation. The Linux stable tree contains multiple fixing commits across supported branches.

Likely exposure

Systems running affected Linux kernels with ext4 filesystems are the relevant exposure. Downstream distribution impact depends on kernel packaging and backports. The bundle includes Debian LTS advisories, indicating distro-level remediation activity, but it does not identify every affected distribution or appliance.

Exploitation context

The evidence is a kernel bug report found by Syzkaller and Linux Verification Center. The source bundle marks KEV as false and provides no cited evidence of exploitation in the wild. Practical impact is not fully characterized in the provided sources.

Researcher notes

Key unknowns are exploitability, privilege impact, and distribution-specific affected ranges. The public record shows memory corruption in ext4 namei handling, fixed in Linux stable commits. Avoid assuming remote reachability; this appears tied to local filesystem operations.

Mitigation direction

  • Apply kernel updates from your Linux distribution or vendor advisory channel.
  • Confirm updates include the referenced Linux stable ext4 fixing commits.
  • Prioritize multi-user systems and hosts running untrusted workloads on ext4.
  • Review Debian LTS announcements if using affected Debian-based systems.
  • If no package is available, follow vendor guidance for temporary risk reduction.

Validation and detection

  • Inventory systems using ext4 filesystems and Linux kernels.
  • Map running kernel packages to vendor advisories or stable commits.
  • Verify the booted kernel is the patched version after maintenance.
  • Check vulnerability scanners for CVE-2025-23150 detection coverage.
  • Document unresolved systems with compensating controls and patch timelines.
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

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CVE-2025-23150 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
2ADP providers
12Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical Impact: partial

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
CISA-ADPCISA ADP Vulnrichment
other:ssvc

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinuxea54176e5821936d109bb45dc2c19bd53559e735, 5872331b3d91820e14716632ebb56b1399b34fe1, 5872331b3d91820e14716632ebb56b1399b34fe1, 5872331b3d91820e14716632ebb56b1399b34fe1, 5872331b3d91820e14716632ebb56b1399b34fe1, 5872331b3d91820e14716632ebb56b1399b34fe1, 5872331b3d91820e14716632ebb56b1399b34fe1, 5872331b3d91820e14716632ebb56b1399b34fe1, 5872331b3d91820e14716632ebb56b1399b34fe1, 059b1480105478c5f68cf664301545b8cad6a7cf, 539ae3e03875dacaa9c388aff141ccbb4ef4ecb5, fbbfd55a40d5d0806b59ee0403c75d5ac517533f, b3ddf6ba5e28a57729fff1605ae08e21be5c92e3, e50fe43e3062e18846e99d9646b9c07b097eb1ed, 88e79f7a9841278fa8ff7ff6178bad12da002ffc, 5.4.61, 4.4.234, 4.9.234, 4.14.195, 4.19.142, 5.7.18, 5.8.4unaffected
LinuxLinux5.9, 0, 5.4.293, 5.10.237, 5.15.181, 6.1.135, 6.6.88, 6.12.24, 6.13.12, 6.14.3, 6.15affected
Weakness

CWE details

No CWE listed

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