Linux Kernel: Out-of-Bounds Access (CVE-2026-68388)
Published Last modified Sources: Ubuntu, Debian LTS, Red Hat, BSI, CVE.org, Msrc Update Guide
What is affected, what to do
A flaw was found in the Linux kernel's Server Message Block (SMB) client. The `smb3_simple_fallocate_range()` function, which manages file allocation, can incorrectly process overlapping allocated ranges provided by a server.
The available sources name no fixed version. Check the vendor guidance in the references below.
Conflicting version data — version display is hidden until the data is resolved.
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Metrics
4.4
Priority
XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.
Source: Vendor (CNA), CVSS v3
4.4
CVSS v3
Severity Medium on the scale from 0 to 10.
Source: Ubuntu, Debian LTS, Red Hat, BSI, CVE.org, Msrc Update Guide
0.5 %
EPSS score
Low — model estimates < 1% exploitation likelihood.
Source: FIRST EPSS, percentile 43.8
Show all metrics
- Severity
- Medium
Priority (0–325)
The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?
Read in glossary- 59.82 Methodology
Exploit maturity
An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.
Read in glossary- no public PoC known
XIEM Effective CVSS
XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.
Read in glossary- 4.4 Methodology
CVSS v3
CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.
Read in glossary- 4.4
EPSS score
The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.
Read in glossary- 0.5 %
- Low — model estimates < 1% exploitation likelihood.
EPSS percentile
The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.
Read in glossary- 43.8
- High — this CVE ranks above the median of all CVEs scored today (rank ≥ 36%).
KEV status
The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.
Read in glossary- —
- Published
- CISA assessment (SSVC)
- Exploitation: none known · automatable · Technical impact: total
- Source: CISA Vulnrichment, as of 16 October 2026
CWE
CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.
Read in glossary- CWE-125
Detection rules
No NEOSEC detection rule is available for this vulnerability yet.
Classification under NIS2 and CRA
Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.
NIS2
NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.
Read in glossary- Handle the vulnerability in regular vulnerability handling under Art. 21(2)(e) NIS2.
CRA
The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.
Read in glossary- From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
ISO/IEC 27001
ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.
Read in glossary- Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.
Description
A flaw was found in the Linux kernel's Server Message Block (SMB) client. The `smb3_simple_fallocate_range()` function, which manages file allocation, can incorrectly process overlapping allocated ranges provided by a server. This can result in parts of a file not being properly zero-filled, leading to potential data integrity issues. More critically, a malformed range length could cause an out-of-bounds read, potentially leading to information disclosure or system instability.
Source: Ubuntu Security Notices, Debian LTS Advisories, redhat_csaf, BSI WID Portal, BSI CSAF, cvelistv5, NVD (NIST), Microsoft Security Update Guide
Affected products
The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.
| Affected versions | Fixed in | ||
|---|---|---|---|
| Linux | Linux |
|
|
| IBM | QRadar SIEM |
|
|
Vendors and products
Affected operating systems
| Linux | debian | linux | bookworm |
| Linux | debian | linux-6.12 | bookworm |
| Linux | ubuntu | linux-gcp-5.15 | focal |
Weakness classes (CWE)
CWE-125Out-of-bounds Read
Base
The product reads data past the end, or before the beginning, of the intended buffer.
Entry at MITRE CWE-125
References & sources
- git.kernel.orgstable/c/437637f5ff3f573b2edf8571de91fb00a21eb4e6
- git.kernel.orgstable/c/377fe3e583e46369ee1004d5cfe12271d6589a68
- git.kernel.orgstable/c/7e08ab7a061b17ac1989a225c6afb53f44a86808
- git.kernel.orgstable/c/a4a09e5142835633fffbde68bd0a039ba4d4bf97
- git.kernel.orgstable/c/b09ae45d85dc816987a71db9eebc54b0ae288e94
- git.kernel.orgstable/c/aeb58a4eb39a7ff4d7782b4f4ada0fda5e0675d2
- git.kernel.orgstable/c/01719883235507b1585e4c51e320d9a7113dc698
- git.kernel.orgstable/c/f47c7277c03a636fcc3a57969f2dc09567b3c050
Changes to this CVE
Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).
Record modifiedCISA ADP
Weakness type: CWE-125
Show the original change
Individual changes of this event as published by NVD Type Action Before After Weakness type (CWE) added —CWE-125Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0
Record modifiedLinux
New references:- https://git.kernel.org/stable/c/01719883235507b1585e4c51e320d9a7113dc698
- https://git.kernel.org/stable/c/377fe3e583e46369ee1004d5cfe12271d6589a68
- https://git.kernel.org/stable/c/437637f5ff3f573b2edf8571de91fb00a21eb4e6
- https://git.kernel.org/stable/c/7e08ab7a061b17ac1989a225c6afb53f44a86808
and 4 more references
Show 16 original changes
Individual changes of this event as published by NVD Type Action Before After Reference added —https://git.kernel.org/stable/c/01719883235507b1585e4c51e320d9a7113dc698Reference added —https://git.kernel.org/stable/c/377fe3e583e46369ee1004d5cfe12271d6589a68Reference added —https://git.kernel.org/stable/c/437637f5ff3f573b2edf8571de91fb00a21eb4e6Reference added —https://git.kernel.org/stable/c/7e08ab7a061b17ac1989a225c6afb53f44a86808Reference added —https://git.kernel.org/stable/c/a4a09e5142835633fffbde68bd0a039ba4d4bf97Reference added —https://git.kernel.org/stable/c/aeb58a4eb39a7ff4d7782b4f4ada0fda5e0675d2Reference added —https://git.kernel.org/stable/c/b09ae45d85dc816987a71db9eebc54b0ae288e94Reference added —https://git.kernel.org/stable/c/f47c7277c03a636fcc3a57969f2dc09567b3c050Reference removed https://git.kernel.org/stable/c/01719883235507b1585e4c51e320d9a7113dc698—Reference removed https://git.kernel.org/stable/c/377fe3e583e46369ee1004d5cfe12271d6589a68—Reference removed https://git.kernel.org/stable/c/437637f5ff3f573b2edf8571de91fb00a21eb4e6—Reference removed https://git.kernel.org/stable/c/7e08ab7a061b17ac1989a225c6afb53f44a86808—Reference removed https://git.kernel.org/stable/c/a4a09e5142835633fffbde68bd0a039ba4d4bf97—Reference removed https://git.kernel.org/stable/c/aeb58a4eb39a7ff4d7782b4f4ada0fda5e0675d2—Reference removed https://git.kernel.org/stable/c/b09ae45d85dc816987a71db9eebc54b0ae288e94—Reference removed https://git.kernel.org/stable/c/f47c7277c03a636fcc3a57969f2dc09567b3c050—Source identifier: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
Record modifiedCISA ADP
CISA assessment (SSVC): exploitation: none known, automatable: yes
Show the original change
Individual changes of this event as published by NVD Type Action Before After SSVC assessment added —{"id":"CVE-2026-68388","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"yes"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2026-10-16T15:47:53.412861Z"}Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0
Record modifiedLinux
Show 4 original changes
Individual changes of this event as published by NVD Type Action Before After Reference added —https://git.kernel.org/stable/c/01719883235507b1585e4c51e320d9a7113dc698Reference added —https://git.kernel.org/stable/c/aeb58a4eb39a7ff4d7782b4f4ada0fda5e0675d2Reference added —https://git.kernel.org/stable/c/f47c7277c03a636fcc3a57969f2dc09567b3c050Affected versions (publisher) changed Linux, LinuxLinux, LinuxSource identifier: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
Record modifiedLinux
1 individual change: Affected versions (publisher)
Show the original change
Individual changes of this event as published by NVD Type Action Before After Affected versions (publisher) changed Linux, LinuxLinux, LinuxSource identifier: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
Show one older change
ReceivedLinux
Description added or changed
New references:- https://git.kernel.org/stable/c/377fe3e583e46369ee1004d5cfe12271d6589a68
- https://git.kernel.org/stable/c/437637f5ff3f573b2edf8571de91fb00a21eb4e6
- https://git.kernel.org/stable/c/7e08ab7a061b17ac1989a225c6afb53f44a86808
- https://git.kernel.org/stable/c/a4a09e5142835633fffbde68bd0a039ba4d4bf97
and 1 more reference
Show 7 original changes
Individual changes of this event as published by NVD Type Action Before After Affected versions (publisher) added —Linux, LinuxDescription added —In the Linux kernel, the following vulnerability has been resolved: smb/client: handle overlapping allocated ranges in fallocate smb3_simple_fallocate_range() can skip holes when an allocated range returned by the server starts before the current fallocate offset. The skipped hole is not zero-filled, but fallocate still returns success. A later write to that hole may therefore fail with ENOSPC. The function queries allocated ranges so that it can preserve existing contents and write zeroes only into holes. However, the server may return a range that starts before the current fallocate offset. For example, assume the fallocate request is [100, 400) and the only allocated range returned by the server is [0, 200): Request: [100, 400) Server range: [ 0, 200) allocated Correct: [100, 200) allocated data, skip [200, 400) hole, zero-fill Current: [100, 300) skipped [300, 400) zero-filled afterwards The current code adds the full server range length, 200, to the current offset 100 and moves to 300. As a result, the hole in [200, 300) is skipped without being zero-filled. Fix this by advancing only over the part of the allocated range that overlaps the current fallocate offset. Ignore ranges that end before the current offset and reject ranges whose end offset overflows. This also prevents a malformed range length from causing an out-of-bounds zero-buffer read.Reference added —https://git.kernel.org/stable/c/377fe3e583e46369ee1004d5cfe12271d6589a68Reference added —https://git.kernel.org/stable/c/437637f5ff3f573b2edf8571de91fb00a21eb4e6Reference added —https://git.kernel.org/stable/c/7e08ab7a061b17ac1989a225c6afb53f44a86808Reference added —https://git.kernel.org/stable/c/a4a09e5142835633fffbde68bd0a039ba4d4bf97Reference added —https://git.kernel.org/stable/c/b09ae45d85dc816987a71db9eebc54b0ae288e94Source identifier: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
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<a href="https://intel.neosec.eu/en/cve/CVE-2026-68388"><img src="https://intel.neosec.eu/badge/cve/CVE-2026-68388.svg?lang=en" alt="CVE-2026-68388 – NEOSEC Intel" height="20"></a>