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Full vulnerability report · 2026
CVE-2026-45659High confidence

Microsoft SharePoint Server Deserialization of Untrusted Data Vulnerability

Microsoft · SharePoint Server

8.8HighCVSS 3.1
Recommended action
Patch now

CISA confirms exploitation in the wild and lists 2026-07-04 as the remediation due date.

Patch available
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityHighOperational priority:Critical, raised one band.upgradedsince 1 Jul 2026

Evidence used

  • CISA confirms exploitation in the wild.
  • EPSS is 2.70% for the current model date.

Compensating controls

  • Validate the affected product branch and deploy the verified fixed release.
  • Restrict the affected network interface to trusted sources where business-safe.
  • Increase monitoring for the attack path and post-exploitation behaviour described in the report.

Verification

  1. Confirm that the asset runs Microsoft SharePoint Server and falls inside the recorded affected range.
  2. Verify the installed build against the product-specific fixed version after deployment.
  3. Validate exposure, authentication requirements and compensating controls in the actual environment.
  4. Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
Mitigation target: Within 3 daysRemediation target: Within 90 days

This automated reassessment organises public evidence. It does not know asset exposure, business impact or control effectiveness and does not replace CVSS or a human risk decision.

Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Choose official national sources for this report. Each advisory shows its original language. Your selection is remembered on this device and included in shared links.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current
ENISA EUVD identifier

EUVD-2026-31518

CISA KEV mirrored by ENISA

Deserialization of untrusted data in Microsoft Office SharePoint allows an authorized attacker to execute code over a network.

EUVD state
Present in the current official mapping
Known exploitation
Recorded by ENISA since 1 Jul 2026. Evidence sources: cisa_kev.
ENISA score
8.8 · CVSS 3.1
Advisory evidence
1 linked advisory record
Recommended actionPatch now

CISA confirms exploitation in the wild and lists 2026-07-04 as the remediation due date.

Patch available
01

What, why and how

Microsoft SharePoint Server contains a deserialization of untrusted data vulnerability which allows an authorized attacker to execute code over a network.

What

Microsoft SharePoint Server contains a deserialization of untrusted data vulnerability which allows an authorized attacker to execute code over a network.

Why

Attacker-influenced serialised data is reconstructed as trusted objects, which can invoke dangerous application behaviour.

How

An attacker operating through a network path may attempt exploitation with low privileges. If successful, the issue may execute code or commands in the affected security context.

What

Microsoft SharePoint Server contains a deserialization of untrusted data vulnerability which allows an authorized attacker to execute code over a network.

Why

Attacker-influenced serialised data is reconstructed as trusted objects, which can invoke dangerous application behaviour.

How

An attacker operating through a network path may attempt exploitation with low privileges. If successful, the issue may execute code or commands in the affected security context.

02

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
Confirmed in the wild

CISA added this CVE to its Known Exploited Vulnerabilities catalogue on 2026-07-01. Known ransomware campaign use is recorded.

Public PoC / exploit material
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
None recorded

No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.

Likely attack path
a network path → Deserialization of Untrusted Data → execute code or commands in the affected security context
Attack surface
Network
Privileges required
Low: a basic authenticated account is required
User interaction
None
Attack complexity
Low: no specialised conditions are recorded
Security boundary
Unchanged: impact remains within the vulnerable component's security authority
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-502 ↗

CWE-502: Deserialization of Untrusted Data. The product deserializes untrusted data without sufficiently ensuring that the resulting data will be valid.

CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C

Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.

AVNetworkAttack vector: The vulnerable component can be reached over a network.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.PRLowPrivileges required: The attacker needs basic user-level privileges.UINoneUser interaction: No action by another user is required.SUnchangedScope: The security impact remains within the vulnerable component's authority.CHighConfidentiality impact: A successful attack can cause a major loss.IHighIntegrity impact: A successful attack can cause a major loss.AHighAvailability impact: A successful attack can cause a major loss.
Post-exploitation / living off the land
After compromise, an attacker may use built-in shells, scripting engines, scheduled tasks and native network utilities for discovery, persistence or movement. This is a plausible LoTL path, not evidence that it has occurred for every attack.
NetworkRemote code executionCWE-502CISA KEV
A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

ENISA EUVD · EUVD-2026-31518Known-exploited evidence recorded

Deserialization of untrusted data in Microsoft Office SharePoint allows an authorized attacker to execute code over a network.

Official EUVD record ↗
BSI · German · WID-SEC-2026-1652Microsoft SharePoint Server 2016 und SharePoint Server 2019: Schwachstelle ermöglicht Codeausführung

Ein entfernter, authentisierter Angreifer kann eine Schwachstelle in Microsoft SharePoint Server 2016, Microsoft SharePoint Server 2019 und Microsoft SharePoint ausnutzen, um beliebigen Programmcode auszuführen.

Official advisory ↗
Canadian Centre for Cyber Security · English · AL26-015AL26-015 - Critical vulnerability impacting Microsoft SharePoint Server – CVE-2026-45659

An Alert is used to raise awareness of a recently identified cyber threat that may impact cyber information assets, and to provide additional detection and mitigation advice to recipients. The Canadian Centre for Cyber Security ("Cyber Centre") is also available to provide additional assistance regarding the content of this Alert to recipients as requested.

Official advisory ↗
Canadian Centre for Cyber Security · English · AV26-456Microsoft security advisory – May 2026 monthly rollup (AV26-456) – Update 3

On May 12, 2026, Microsoft published security advisories to address vulnerabilities in multiple products. Included were critical updates for the following products: On May 21, 2026, Microsoft published an out-of-band (OOB) security update to address CVE-2026-45659, an additional vulnerability impacting Microsoft SharePoint Enterprise Server 2019, Microsoft SharePoint Server 2016 and Microsoft SharePoint Server Subscription Edition. The CVE was inadvertently omitted from the May 2026 Security Updates.

Official advisory ↗
CERT-FR · French · CERTFR-2026-AVI-0634Vulnérabilité dans les produits Microsoft

Une vulnérabilité a été découverte dans les produits Microsoft. Elle permet à un attaquant de provoquer une exécution de code arbitraire à distance.

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2026-017240マイクロソフトのMicrosoft SharePoint Serverにおける信頼できないデータのデシリアライゼーションに関する脆弱性

Microsoft Office SharePointにおいて、信頼されていないデータのデシリアライズの脆弱性により、認可された攻撃者がネットワーク経由でコードを実行できる可能性があります。

Official advisory ↗
KISA KrCERT/CC · Korean · KNVD-6867美 CISA 발표 주요 Exploit 정보공유(Update. 2026-07-01)

Microsoft SharePoint Server Deserialization of Untrusted Data Vulnerability

Official advisory ↗
03

Patch and workaround

Operational remediation based on structured source evidence.

Status
?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Patch available
Affected
Fixed
The Cyber Centre recommends that organizations upgrade affected Microsoft SharePoint instances to a fixed version: Affected Product Affected Versions Fixed Versions Microsoft SharePoint Enterprise Server 2016 16.0.0 before 16.0.5552.1002 16.0.5552.1002 Microsoft SharePoint Server 2019 16.0.0 before 16.0.10417.20128 16.0.10417.20128 Microsoft SharePoint Server Subscription Edition 16.0.0 before 16.0.19725.20280 16.0.19725.20280 The Cyber Centre recommends organizations: Identify all on-premises SharePoint Server instances, particularly those exposed to the internet. Use or upgrade to supported versions of on-premises Microsoft SharePoint Server. Apply the latest security updates from Microsoft. Important note: Microsoft SharePoint Enterprise Server 2016 Footnote 6 and Server 2019 Footnote 7 will be end of life on July 14, 2026 . Organizations are urged to migrate to a supported version. In addition, the Cyber Centre strongly recommends that organizations review and implement the Cyber Centre’s Top 10 IT Security Actions with an emphasis on the following topics Footnote 8 . Patch operating systems and applications Harden operating systems and applications Isolate web-facing applications Should activity matching the content of this alert be discovered, recipients are encouraged to report via My Cyber Portal , or email contact@cyber.gc.ca .
Action
Apply the fixed release for the affected product branch as recorded by Canadian Centre for Cyber Security. Validate the exact product and build in the linked advisory before deployment.
Workaround
No verified workaround is recorded. If business-safe, reduce exposure to the affected interface and allow only trusted sources until authoritative guidance is available.
04

Evidence and provenance

Published 22 May 2026 · Last source change 11 Aug 2026, 03:55 UTC · CWE-502 · Deserialization of Untrusted Data

CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source
?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.
FIRST · tracked since 2026-08-14
European sourceENISA EUVD · EUVD-2026-31518
Product sourceCISA KEV
Remediation sourceCVE/CNA references
CWE sourceOther authority
NVD statusNVD enriched

Core structured fields are present and their contributing authorities are shown above.

Material change intelligence

What changed after publication

View recent updates ↗
  1. Vendor guidanceAuthoritative vendor guidance changed: removed remediation: cyber.gc.ca/al26-015-critical-vulnerability-impacting-microsoft-sharepoint-server-cve-2026-45659.
    Before
    remediation: cyber.gc.ca/al26-015-critical-vulnerability-impacting-microsoft-sharepoint-server-cve-2026-45659 · vendor advisory: msrc.microsoft.com/CVE-2026-45659
    After
    vendor advisory: msrc.microsoft.com/CVE-2026-45659
    secure@microsoft.com ↗
  2. Affected versionsThe structured affected or fixed version information changed.
    Before
    Microsoft SharePoint Enterprise Server 2016: 16.0.0 < 16.0.5552.1002; Microsoft SharePoint Server 2019: 16.0.0 < 16.0.10417.20128; Microsoft SharePoint Server Subscription Edition: 16.0.0 < 16.0.19725.20280 · Fixed: The Cyber Centre recommends that organizations upgrade affected Microsoft SharePoint instances to a fixed version: Affected Product Affected Versions Fixed Versions Microsoft SharePoint Enterprise Server 2016 16.0.0 before 16.0.5552.1002 16.0.5552.1002 Microsoft SharePoint Server 2019 16.0.0 before 16.0.10417.20128 16.0.10417.20128 Microsoft SharePoint Server Subscription Edition 16.0.0 before 16.0.19725.20280 16.0.19725.20280 The Cyber Centre recommends organizations: Identify all on-premises SharePoint Server instances, particularly those exposed to the internet. Use or upgrade to supported versions of on-premises Microsoft SharePoint Server. Apply the latest security updates from Microsoft. Important note: Microsoft SharePoint Enterprise Server 2016 Footnote 6 and Server 2019 Footnote 7 will be end of life on July 14, 2026 . Organizations are urged to migrate to a supported version. In addition, the Cyber Centre strongly recommends that organizations review and implement the Cyber Centre’s Top 10 IT Security Actions with an emphasis on the following topics Footnote 8 . Patch operating systems and applications Harden operating systems and applications Isolate web-facing applications Should activity matching the content of this alert be discovered, recipients are encouraged to report via My Cyber Portal , or email contact@cyber.gc.ca .
    After
    Microsoft SharePoint Enterprise Server 2016: 16.0.0 < 16.0.5552.1002; Microsoft SharePoint Server 2019: 16.0.0 < 16.0.10417.20128; Microsoft SharePoint Server Subscription Edition: 16.0.0 < 16.0.19725.20280 · Fixed: No fixed version is explicitly recorded in the structured CVE data.
    CISA KEV ↗
  3. Remediation statusRemediation status changed from Patch available to Awaiting fix.
    Before
    Patch available
    After
    Awaiting fix
    secure@microsoft.com ↗
  4. Affected versionsThe structured affected or fixed version information changed.
    Before
    16.0.0 < 16.0.5552.1002; 16.0.0 < 16.0.10417.20128; 16.0.0 < 16.0.19725.20280 · Fixed: No fixed version is explicitly recorded in the structured CVE data.
    After
    Microsoft SharePoint Enterprise Server 2016: 16.0.0 < 16.0.5552.1002; Microsoft SharePoint Server 2019: 16.0.0 < 16.0.10417.20128; Microsoft SharePoint Server Subscription Edition: 16.0.0 < 16.0.19725.20280 · Fixed: No fixed version is explicitly recorded in the structured CVE data.
    CNA ↗
  5. Affected versionsThe structured affected or fixed version information changed.
    Before
    Microsoft SharePoint Enterprise Server 2016: 16.0.0 < 16.0.5552.1002; Microsoft SharePoint Server 2019: 16.0.0 < 16.0.10417.20128; Microsoft SharePoint Server Subscription Edition: 16.0.0 < 16.0.19725.20280 · Fixed: No fixed version is explicitly recorded in the structured CVE data.
    After
    Microsoft SharePoint Enterprise Server 2016: 16.0.0 < 16.0.5552.1002; Microsoft SharePoint Server 2019: 16.0.0 < 16.0.10417.20128; Microsoft SharePoint Server Subscription Edition: 16.0.0 < 16.0.19725.20280 · Fixed: The Cyber Centre recommends that organizations upgrade affected Microsoft SharePoint instances to a fixed version: Affected Product Affected Versions Fixed Versions Microsoft SharePoint Enterprise Server 2016 16.0.0 before 16.0.5552.1002 16.0.5552.1002 Microsoft SharePoint Server 2019 16.0.0 before 16.0.10417.20128 16.0.10417.20128 Microsoft SharePoint Server Subscription Edition 16.0.0 before 16.0.19725.20280 16.0.19725.20280 The Cyber Centre recommends organizations: Identify all on-premises SharePoint Server instances, particularly those exposed to the internet. Use or upgrade to supported versions of on-premises Microsoft SharePoint Server. Apply the latest security updates from Microsoft. Important note: Microsoft SharePoint Enterprise Server 2016 Footnote 6 and Server 2019 Footnote 7 will be end of life on July 14, 2026 . Organizations are urged to migrate to a supported version. In addition, the Cyber Centre strongly recommends that organizations review and implement the Cyber Centre’s Top 10 IT Security Actions with an emphasis on the following topics Footnote 8 . Patch operating systems and applications Harden operating systems and applications Isolate web-facing applications Should activity matching the content of this alert be discovered, recipients are encouraged to report via My Cyber Portal , or email contact@cyber.gc.ca .
    Canadian Centre for Cyber Security ↗
  6. Remediation statusRemediation status changed from Awaiting fix to Patch available.
    Before
    Awaiting fix
    After
    Patch available
    Canadian Centre for Cyber Security ↗
Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Added to CISA KEV
Fixed release recorded from official guidance
ENISA EUVD · EUVD-2026-31518↗Canadian Centre for Cyber Security remediation guidance↗CISA KEV record↗CVE authority or vendor reference↗Official CVE record (CNA and ADP data)↗NVD record↗
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
Free version - for non-commercial use only.CVE-2026-45659 · cve.blacktree.nl