Linux Kernel: Out-of-Bounds Write (CVE-2026-99083)
Published Last modified Sources: Msrc Update Guide, CVE.org, BSI
What is affected, what to do
In the Linux kernel, the following vulnerability has been resolved: ksmbd: fix heap out-of-bounds write in krb5_authenticate() In krb5_authenticate(), out_len is calculated to determine available headroom in response_buf for the incoming Kerberos AP-REP token. However, when SMB2_SESSION_SETUP is processed as a non-first element of a compounded SMB2 request, the calculation omits work->next_smb2_rsp_hdr_off.
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
8.8
Priority
XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.
Source: Vendor (CNA), CVSS v3
8.8
CVSS v3
Severity High on the scale from 0 to 10.
Source: Msrc Update Guide, CVE.org, BSI
0.4 %
EPSS score
Low — model estimates < 1% exploitation likelihood.
Source: FIRST EPSS, percentile 38.7
Show all metrics
- Severity
- High
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- 85.98 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- 8.8 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- 8.8
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- 0.4 %
- 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- 38.7
- 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
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- High technical severity: assess and remediate the vulnerability in vulnerability handling under Art. 21(2)(e) NIS2 and document the decision.
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
In the Linux kernel, the following vulnerability has been resolved: ksmbd: fix heap out-of-bounds write in krb5_authenticate() In krb5_authenticate(), out_len is calculated to determine available headroom in response_buf for the incoming Kerberos AP-REP token. However, when SMB2_SESSION_SETUP is processed as a non-first element of a compounded SMB2 request, the calculation omits work->next_smb2_rsp_hdr_off. This causes out_len to overstate remaining buffer headroom by the cumulative size of prior responses in the compound chain. Consequently, the length check in ksmbd_krb5_authenticate() (*out_len <= resp->spnego_blob_len) passes erroneously, allowing memcpy() to write the AP-REP blob past the end of response_buf into adjacent kernel heap memory. Fix this by subtracting work->next_smb2_rsp_hdr_off when computing out_len, ensuring it accurately reflects physical remaining buffer space.
Source: Microsoft Security Update Guide, cvelistv5, NVD (NIST), BSI CSAF, BSI WID Portal
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 |
|
|
Vendors and products
References & sources
- git.kernel.orgstable/c/23a0be6a84a38ac169eeab49017934e8e27c65f0
- git.kernel.orgstable/c/4722d06b2907585074252061b1024a696c1cfc23
- git.kernel.orgstable/c/517404e157395d0f8da125ca956c566895dfcd06
- git.kernel.orgstable/c/59c6dcc5dd9dafe764ca0d40525933b2be69b059
- git.kernel.orgstable/c/80af1bde97d5a85ad6f2c40ca894ccc8fa75a27a
- git.kernel.orgstable/c/1f73a6d40f4d1bae4f3491c0ec1ea8ee6ce035ff
- git.kernel.orgstable/c/a07dfb33112a42437f9d2d0bfd35c68575257381
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 modifiedLinux
Show 3 original changes
Individual changes of this event as published by NVD Type Action Before After Affected versions (publisher) added —Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/99xxx/CVE-2026-99083.json">CVE-2026-99083</a>Reference added —https://git.kernel.org/stable/c/1f73a6d40f4d1bae4f3491c0ec1ea8ee6ce035ffReference added —https://git.kernel.org/stable/c/a07dfb33112a42437f9d2d0bfd35c68575257381Source identifier: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
Record modifiedLinux
CVSS V3.1: AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Show the original change
Individual changes of this event as published by NVD Type Action Before After CVSS added —AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:HSource identifier: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
ReceivedLinux
Description added or changed
New references:- https://git.kernel.org/stable/c/23a0be6a84a38ac169eeab49017934e8e27c65f0
- https://git.kernel.org/stable/c/4722d06b2907585074252061b1024a696c1cfc23
- https://git.kernel.org/stable/c/517404e157395d0f8da125ca956c566895dfcd06
- https://git.kernel.org/stable/c/59c6dcc5dd9dafe764ca0d40525933b2be69b059
and 1 more reference
Show 7 original changes
Individual changes of this event as published by NVD Type Action Before After Description added —In the Linux kernel, the following vulnerability has been resolved: ksmbd: fix heap out-of-bounds write in krb5_authenticate() In krb5_authenticate(), out_len is calculated to determine available headroom in response_buf for the incoming Kerberos AP-REP token. However, when SMB2_SESSION_SETUP is processed as a non-first element of a compounded SMB2 request, the calculation omits work->next_smb2_rsp_hdr_off. This causes out_len to overstate remaining buffer headroom by the cumulative size of prior responses in the compound chain. Consequently, the length check in ksmbd_krb5_authenticate() (*out_len <= resp->spnego_blob_len) passes erroneously, allowing memcpy() to write the AP-REP blob past the end of response_buf into adjacent kernel heap memory. Fix this by subtracting work->next_smb2_rsp_hdr_off when computing out_len, ensuring it accurately reflects physical remaining buffer space.Affected versions (publisher) added —New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/99xxx/CVE-2026-99083.json">CVE-2026-99083</a>Reference added —https://git.kernel.org/stable/c/23a0be6a84a38ac169eeab49017934e8e27c65f0Reference added —https://git.kernel.org/stable/c/4722d06b2907585074252061b1024a696c1cfc23Reference added —https://git.kernel.org/stable/c/517404e157395d0f8da125ca956c566895dfcd06Reference added —https://git.kernel.org/stable/c/59c6dcc5dd9dafe764ca0d40525933b2be69b059Reference added —https://git.kernel.org/stable/c/80af1bde97d5a85ad6f2c40ca894ccc8fa75a27aSource identifier: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
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<a href="https://intel.neosec.eu/en/cve/CVE-2026-99083"><img src="https://intel.neosec.eu/badge/cve/CVE-2026-99083.svg?lang=en" alt="CVE-2026-99083 – NEOSEC Intel" height="20"></a>