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CVE Record

CVE-2025-40054: f2fs: fix UAF issue in f2fs_merge_page_bio()

In the Linux kernel, the following vulnerability has been resolved: f2fs: fix UAF issue in f2fs_merge_page_bio() As JY reported in bugzilla [1], Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000 pc : [0xffffffe51d249484] f2fs_is_cp_guaranteed+0x70/0x98 lr : [0xffffffe51d24adbc] f2fs_merge_page_bio+0x520/0x6d4 CPU: 3 UID: 0 PID: 6790 Comm: kworker/u16:3 Tainted: P B W OE 6.12.30-android16-5-maybe-dirty-4k #1 5f7701c9cbf727d1eebe77c89bbbeb3371e895e5 Tainted: [P]=PROPRIETARY_MODULE, [B]=BAD_PAGE, [W]=WARN, [O]=OOT_MODULE, [E]=UNSIGNED_MODULE Workqueue: writeback wb_workfn (flush-254:49) Call trace: f2fs_is_cp_guaranteed+0x70/0x98 f2fs_inplace_write_data+0x174/0x2f4 f2fs_do_write_data_page+0x214/0x81c f2fs_write_single_data_page+0x28c/0x764 f2fs_write_data_pages+0x78c/0xce4 do_writepages+0xe8/0x2fc __writeback_single_inode+0x4c/0x4b4 writeback_sb_inodes+0x314/0x540 __writeback_inodes_wb+0xa4/0xf4 wb_writeback+0x160/0x448 wb_workfn+0x2f0/0x5dc process_scheduled_works+0x1c8/0x458 worker_thread+0x334/0x3f0 kthread+0x118/0x1ac ret_from_fork+0x10/0x20 [1] https://bugzilla.kernel.org/show_bug.cgi?id=220575 The panic was caused by UAF issue w/ below race condition: kworker - writepages - f2fs_write_cache_pages - f2fs_write_single_data_page - f2fs_do_write_data_page - f2fs_inplace_write_data - f2fs_merge_page_bio - add_inu_page : cache page #1 into bio & cache bio in io->bio_list - f2fs_write_single_data_page - f2fs_do_write_data_page - f2fs_inplace_write_data - f2fs_merge_page_bio - add_inu_page : cache page #2 into bio which is linked in io->bio_list write - f2fs_write_begin : write page #1 - f2fs_folio_wait_writeback - f2fs_submit_merged_ipu_write - f2fs_submit_write_bio : submit bio which inclues page #1 and #2 software IRQ - f2fs_write_end_io - fscrypt_free_bounce_page : freed bounced page which belongs to page #2 - inc_page_count( , WB_DATA_TYPE(data_folio), false) : data_folio points to fio->encrypted_page the bounced page can be freed before accessing it in f2fs_is_cp_guarantee() It can reproduce w/ below testcase: Run below script in shell #1: for ((i=1;i>0;i++)) do xfs_io -f /mnt/f2fs/enc/file \ -c "pwrite 0 32k" -c "fdatasync" Run below script in shell #2: for ((i=1;i>0;i++)) do xfs_io -f /mnt/f2fs/enc/file \ -c "pwrite 0 32k" -c "fdatasync" So, in f2fs_merge_page_bio(), let's avoid using fio->encrypted_page after commit page into internal ipu cache.

HighCVSS 7.8Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

A race in Linux F2FS filesystem write processing can access an already-freed encrypted page, causing a kernel crash and potentially broader memory-safety impact. Exploitation requires local, low-privileged access and an affected system using the relevant F2FS path. Availability is the clearest demonstrated business risk.

Executive priority

Treat as a high-priority stability and isolation issue where affected F2FS systems permit untrusted local activity. Patch exposed multi-user, mobile, appliance, or container-hosting systems first. Systems without F2FS are unlikely to reach this flaw. Current sources do not justify an emergency response based on active exploitation.

Technical view

CVE-2025-40054 is a use-after-free in f2fs_merge_page_bio(). Concurrent write and writeback activity can submit a cached bio and free an encryption bounce page before later code accesses fio->encrypted_page. The reported failure was a kernel NULL-pointer dereference during F2FS writeback. Linux stable commits change the code to avoid using that page after caching.

Likely exposure

Exposure is concentrated in systems running affected Linux kernel builds with F2FS, particularly encrypted F2FS files undergoing concurrent writes and writeback. The supplied affected-version data spans several kernel series but is insufficiently structured to identify every vulnerable or fixed package build. Distribution and device-vendor backports must be checked individually.

Exploitation context

The CVSS 3.1 score is 7.8 with local access, low privileges, low complexity, and no user interaction. A concurrent-write testcase reproduced a kernel panic. The bundle reports no CISA KEV listing and provides no evidence of active exploitation, public weaponization, or reliable confidentiality and integrity impact in practice.

Researcher notes

The reported crash occurred on a tainted Android-derived 6.12.30 kernel, but Linux stable fixes cover multiple branches. The demonstrated outcome is a panic during concurrent encrypted F2FS writes. Although the CVSS vector assigns high confidentiality, integrity, and availability impacts, the supplied evidence does not establish dependable privilege escalation, information disclosure, or arbitrary code execution.

Mitigation direction

  • Upgrade to a vendor-supported kernel containing the applicable Linux stable fix or vendor backport.
  • Prioritize encrypted F2FS systems that run untrusted or low-privileged local workloads.
  • Restrict unnecessary local access until affected systems can be updated.
  • Consult distribution or device-vendor guidance for exact fixed package and firmware versions.

Validation and detection

  • Inventory running kernel builds and systems with active F2FS mounts.
  • Determine whether F2FS encryption is used on affected systems.
  • Verify the installed kernel contains the applicable listed stable commit or vendor backport.
  • Review kernel logs for F2FS writeback crashes, NULL-pointer dereferences, or related panic traces.
  • After upgrading and rebooting, confirm the running kernel matches the remediated build.
Prepared
Confidence
high
Sources
9

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-2025-40054 mapping review

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Vulnerability profileCVE Program record
Severity
High
CVSS
7.8 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/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
0ADP providers
8Source 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
7.8CVSS 3.1HighCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H1.85.9Linux

Vulnerability scoring details

Base CVSS 3.1 score

7.8High
CVSS 3.1 vector shape for CVE-2025-40054Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

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

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux0b20fcec8651569935a10afe03fedc0b812d044e, 0b20fcec8651569935a10afe03fedc0b812d044e, 0b20fcec8651569935a10afe03fedc0b812d044e, 0b20fcec8651569935a10afe03fedc0b812d044e, 0b20fcec8651569935a10afe03fedc0b812d044e, 0b20fcec8651569935a10afe03fedc0b812d044e, 0b20fcec8651569935a10afe03fedc0b812d044eunaffected
LinuxLinux5.5, 0, 5.10.266, 5.15.217, 6.1.184, 6.6.153, 6.12.105, 6.17.3, 6.18affected
Weakness

CWE details

No CWE listed

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