LiveActive security incident?Get immediate response
CVE Record

CVE-2025-39899: mm/userfaultfd: fix kmap_local LIFO ordering for CONFIG_HIGHPTE

In the Linux kernel, the following vulnerability has been resolved: mm/userfaultfd: fix kmap_local LIFO ordering for CONFIG_HIGHPTE With CONFIG_HIGHPTE on 32-bit ARM, move_pages_pte() maps PTE pages using kmap_local_page(), which requires unmapping in Last-In-First-Out order. The current code maps dst_pte first, then src_pte, but unmaps them in the same order (dst_pte, src_pte), violating the LIFO requirement. This causes the warning in kunmap_local_indexed(): WARNING: CPU: 0 PID: 604 at mm/highmem.c:622 kunmap_local_indexed+0x178/0x17c addr \!= __fix_to_virt(FIX_KMAP_BEGIN + idx) Fix this by reversing the unmap order to respect LIFO ordering. This issue follows the same pattern as similar fixes: - commit eca6828403b8 ("crypto: skcipher - fix mismatch between mapping and unmapping order") - commit 8cf57c6df818 ("nilfs2: eliminate staggered calls to kunmap in nilfs_rename") Both of which addressed the same fundamental requirement that kmap_local operations must follow LIFO ordering.

MediumCVSS 5.5Not KEV-listedUpdated
Discuss exposureBack to CVEs
Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

This is a Linux kernel availability bug affecting a narrow configuration: 32-bit ARM kernels using CONFIG_HIGHPTE. A local low-privileged user may be able to trigger a kernel warning or failure path. The published scoring shows no confidentiality or integrity impact, but high availability impact.

Executive priority

Treat as a targeted availability issue, not a broad enterprise emergency. Patch affected ARM Linux systems through normal kernel maintenance, with faster handling where local untrusted access exists or uptime requirements are strict.

Technical view

In move_pages_pte(), dst_pte and src_pte are mapped with kmap_local_page() but unmapped in FIFO order instead of required LIFO order. On 32-bit ARM with CONFIG_HIGHPTE, this violates kmap_local semantics and can trigger kunmap_local_indexed() warnings, with availability impact.

Likely exposure

Exposure appears limited to affected Linux kernels on 32-bit ARM systems with CONFIG_HIGHPTE enabled. The CVSS vector requires local access with low privileges and no user interaction. Non-ARM systems or kernels without CONFIG_HIGHPTE are not indicated as affected by the provided sources.

Exploitation context

The source bundle does not show CISA KEV listing or any cited evidence of active exploitation. The CVSS vector indicates local exploitation requiring low privileges. No exploit details or weaponized public activity are provided in the supplied sources.

Researcher notes

The record identifies the flaw as an ordering bug in kmap_local unmapping within mm/userfaultfd. The affected-version data is sparse and commit-oriented, so distribution-specific exposure should be confirmed through vendor advisories or kernel backport metadata.

Mitigation direction

  • Check distro or vendor kernel advisories for CVE-2025-39899 fixed packages.
  • Update to a kernel containing the cited stable fixes.
  • Prioritize affected 32-bit ARM systems with local untrusted users.
  • Reboot into the fixed kernel after patching.
  • If no package exists, follow vendor guidance for backport availability.

Validation and detection

  • Inventory Linux kernel versions on 32-bit ARM systems.
  • Check whether CONFIG_HIGHPTE is enabled in deployed kernels.
  • Confirm the relevant stable commits are present or backported.
  • Verify systems rebooted into the patched kernel.
  • Review kernel logs for the cited kunmap_local_indexed warning.
Prepared
Confidence
medium
Sources
5

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.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cve · low confidence lookup

CVE-2025-39899 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

Open ATT&CK lookup
Vulnerability profileCVE Program record
Severity
Medium
CVSS
5.5 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:L/AC:L/PR:L/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
4Source links

SSVC decision data

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

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
5.5CVSS 3.1MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H1.83.6CISA-ADP

Vulnerability scoring details

Base CVSS 3.1 score

5.5Medium
CVSS 3.1 vector shape for CVE-2025-39899Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:L/AC:L/PR:L/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

CISA-ADPCISA ADP Vulnrichment
cvssV3_1other:ssvc

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinuxadef440691bab824e39c1b17382322d195e1fab0, adef440691bab824e39c1b17382322d195e1fab0, adef440691bab824e39c1b17382322d195e1fab0unaffected
LinuxLinux6.8, 0, 6.12.46, 6.16.6, 6.17affected
Weakness

CWE details

No CWE listed

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.