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CVE Record

CVE-2025-39904: arm64: kexec: initialize kexec_buf struct in load_other_segments()

In the Linux kernel, the following vulnerability has been resolved: arm64: kexec: initialize kexec_buf struct in load_other_segments() Patch series "kexec: Fix invalid field access". The kexec_buf structure was previously declared without initialization. commit bf454ec31add ("kexec_file: allow to place kexec_buf randomly") added a field that is always read but not consistently populated by all architectures. This un-initialized field will contain garbage. This is also triggering a UBSAN warning when the uninitialized data was accessed: ------------[ cut here ]------------ UBSAN: invalid-load in ./include/linux/kexec.h:210:10 load of value 252 is not a valid value for type '_Bool' Zero-initializing kexec_buf at declaration ensures all fields are cleanly set, preventing future instances of uninitialized memory being used. An initial fix was already landed for arm64[0], and this patchset fixes the problem on the remaining arm64 code and on riscv, as raised by Mark. Discussions about this problem could be found at[1][2]. This patch (of 3): The kexec_buf structure was previously declared without initialization. commit bf454ec31add ("kexec_file: allow to place kexec_buf randomly") added a field that is always read but not consistently populated by all architectures. This un-initialized field will contain garbage. This is also triggering a UBSAN warning when the uninitialized data was accessed: ------------[ cut here ]------------ UBSAN: invalid-load in ./include/linux/kexec.h:210:10 load of value 252 is not a valid value for type '_Bool' Zero-initializing kexec_buf at declaration ensures all fields are cleanly set, preventing future instances of uninitialized memory being used.

MediumCVSS 5.5Not KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

CVE-2025-39904 is a Linux kernel bug in arm64 kexec handling. A structure was used before all fields were initialized, which could make the kernel read garbage data. The reported impact is availability loss, meaning a local low-privileged attacker could potentially cause a system disruption, not data theft or integrity loss.

Executive priority

Treat this as a moderate-priority reliability and local hardening issue. It does not indicate remote compromise, data exposure, or confirmed exploitation, but kernel availability impact warrants normal patch-cycle remediation, faster on shared or sensitive hosts.

Technical view

The issue is CWE-908 in Linux kernel kexec code. A kexec_buf structure in load_other_segments() was declared without zero-initialization after a later change added a Boolean field that is always read. UBSAN reported invalid Boolean loads. The fix zero-initializes kexec_buf so unread fields start cleanly.

Likely exposure

Exposure is mainly Linux systems using affected kernel builds on arm64 kexec code paths. The CVE source lists Linux kernel versions including 6.16 and 6.17-related entries, but downstream vendor package status must be verified separately.

Exploitation context

The CVSS vector is local, low complexity, low privileges, no user interaction, with high availability impact only. The source bundle does not show CISA KEV listing or evidence of active exploitation.

Researcher notes

The evidence supports an uninitialized kexec_buf field read in arm64 kexec code, fixed by zero-initialization. The bundle references two kernel stable commits. It does not provide exploit proof, downstream package mappings, or a non-patch mitigation.

Mitigation direction

  • Apply Linux kernel updates containing the referenced stable fixes.
  • Check your distribution vendor advisories for backported kernel packages.
  • Prioritize exposed multi-user systems where local users can execute code.
  • If patching is delayed, monitor vendor guidance for supported mitigations.

Validation and detection

  • Inventory Linux kernel versions and architectures across affected fleets.
  • Confirm whether deployed kernels include the referenced stable commits.
  • Check distribution security trackers for package-level fixed versions.
  • Review logs for UBSAN invalid-load reports in kexec paths.
Prepared
Confidence
high
Sources
4

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

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cwe · low confidence lookup

CWE-908: Exact CWE lookup

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cve · low confidence lookup

CVE-2025-39904 mapping review

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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
3Source 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-2025-39904Attack 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
LinuxLinuxbf454ec31add6790f6cdc88328e38901fcbbade6, bf454ec31add6790f6cdc88328e38901fcbbade6unaffected
LinuxLinux6.16, 0, 6.16.8, 6.17affected
Weakness

CWE details

CWE-908

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

CWE-908 · source CWE mapping

Use of Uninitialized Resource

Use of Uninitialized Resource represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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