Evidence used
- CISA confirms exploitation in the wild.
- The selected CVSS metric records a network-reachable, unauthenticated path with no user interaction.
- EPSS is 15.87% for the current model date.
BlackTreeCVE IntelligenceFull vulnerability report · 2026
CVE-2026-58644High confidence
Microsoft SharePoint Deserialization of Untrusted Data Vulnerability
Microsoft · SharePoint
9.8CriticalCVSS 3.1
Patch now
Patch availableCISA confirms exploitation in the wild and lists 2026-07-19 as the remediation due date.
R
Open reassessment dashboard →Operational reassessment
Published severity in operational context
Published severityCritical→Operational priority:Critical, unchanged from published severity.unchanged
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
- Confirm that the asset runs Microsoft SharePoint and falls inside the recorded affected range.
- Verify the installed build against the product-specific fixed version after deployment.
- Validate exposure, authentication requirements and compensating controls in the actual environment.
- Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
CISA confirms exploitation in the wild and lists 2026-07-19 as the remediation due date.
Patch available01
What, why and how
Microsoft SharePoint contains a deserialization of untrusted data vulnerability that allows an unauthorized attacker to execute code over a network.
What
Microsoft SharePoint contains a deserialization of untrusted data vulnerability that allows an unauthorized 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 without authentication or user interaction. If successful, the issue may execute code or commands in the affected security context.
What
Microsoft SharePoint contains a deserialization of untrusted data vulnerability that allows an unauthorized 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 without authentication or user interaction. 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 in the wild
?
Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.CISA added this CVE to its Known Exploited Vulnerabilities catalogue on 2026-07-16.
Public PoC / exploit material None recorded
?
Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.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
- None: unauthenticated exploitation is possible
- 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:N/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:CCommon 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.PRNonePrivileges required: The attacker does not need an account or existing 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.
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
- 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 14 Jul 2026 · Last source change 8 Oct 2026, 18:13 UTC · CWE-502 · Deserialization of Untrusted Data
CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source FIRST · tracked since 2026-08-14
?
The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.European sourceENISA EUVD · EUVD-2026-43779
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
View recent updates ↗What changed after publication
- Vendor guidanceAuthoritative vendor guidance changed: added remediation: msrc.microsoft.com/CVE-2026-58644; removed remediation: cyber.gc.ca/al26-017-critical-vulnerabilities-impacting-microsoft-sharepoint-server-cve-2026-56164-cve-2026-55040-cve-2026-58644.secure@microsoft.com ↗
- Before
- patch: msrc.microsoft.com/CVE-2026-58644 · remediation: cyber.gc.ca/al26-017-critical-vulnerabilities-impacting-microsoft-sharepoint-server-cve-2026-56164-cve-2026-55040-cve-2026-58644
- After
- patch: msrc.microsoft.com/CVE-2026-58644 · remediation: msrc.microsoft.com/CVE-2026-58644
- Affected versionsThe structured affected or fixed version information changed.CISA KEV ↗
- Before
- Microsoft SharePoint Enterprise Server 2016: 16.0.0 < 16.0.5556.1005; Microsoft SharePoint Server 2019: 16.0.0 < 16.0.10417.20153; Microsoft SharePoint Server Subscription Edition: 16.0.0 < 16.0.19725.20384 · 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 16.0.5561.1001 16.0.5561.1001 Microsoft SharePoint Server 2019 16.0.0 before 16.0.10417.20175 16.0.10417.20175 Microsoft SharePoint Server Subscription Edition 16.0.0 before 16.0.19725.20434 16.0.19725.20434 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 to all affected SharePoint Servers including (Subscription Edition, 2019, and 2016) Monitor SharePoint servers for suspicious activity, including unusual requests, web shells, malicious processes, unauthorized access attempts, and machine key theft indicators Harden SharePoint Deployments: Enable Antimalware Scan Interface (AMSI) integration for SharePoint web applications Configure AMSI Request Body Scan Mode to Full Mode where operationally feasible Restrict or eliminate direct Internet exposure of SharePoint servers whenever possible Limit access to SharePoint Central Administration and management interfaces Monitor for Indicators of Compromise: Organizations should closely monitor SharePoint environments for: Unexpected privilege escalation activity Unauthorized authentication attempts Suspicious IIS machine key access Evidence of deserialization attacks or web shell deployment Microsoft Defender and AMSI detections related to SharePoint exploitation activity Important note: Microsoft SharePoint Enterprise Server 2016 Footnote 11 and Server 2019 Footnote 12 are end of life as of 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 13 . 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 < 16.0.5556.1005; Microsoft SharePoint Server 2019: 16.0.0 < 16.0.10417.20153; Microsoft SharePoint Server Subscription Edition: 16.0.0 < 16.0.19725.20384 · Fixed: An authoritative update reference is available, but the fixed version is not recorded in the structured CVE fields. Check the linked vendor advisory for the applicable release.
- Vendor guidanceAuthoritative vendor guidance changed: added remediation: msrc.microsoft.com/CVE-2026-58644; removed remediation: cyber.gc.ca/al26-017-critical-vulnerabilities-impacting-microsoft-sharepoint-server-cve-2026-56164-cve-2026-55040-cve-2026-58644.secure@microsoft.com ↗
- Before
- patch: msrc.microsoft.com/CVE-2026-58644 · remediation: cyber.gc.ca/al26-017-critical-vulnerabilities-impacting-microsoft-sharepoint-server-cve-2026-56164-cve-2026-55040-cve-2026-58644
- After
- patch: msrc.microsoft.com/CVE-2026-58644 · remediation: msrc.microsoft.com/CVE-2026-58644
- Affected versionsThe structured affected or fixed version information changed.CISA KEV ↗
- Before
- Microsoft SharePoint Enterprise Server 2016: 16.0.0 < 16.0.5556.1005; Microsoft SharePoint Server 2019: 16.0.0 < 16.0.10417.20153; Microsoft SharePoint Server Subscription Edition: 16.0.0 < 16.0.19725.20384 · 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 16.0.5561.1001 16.0.5561.1001 Microsoft SharePoint Server 2019 16.0.0 before 16.0.10417.20175 16.0.10417.20175 Microsoft SharePoint Server Subscription Edition 16.0.0 before 16.0.19725.20434 16.0.19725.20434 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 to all affected SharePoint Servers including (Subscription Edition, 2019, and 2016) Monitor SharePoint servers for suspicious activity, including unusual requests, web shells, malicious processes, unauthorized access attempts, and machine key theft indicators Harden SharePoint Deployments: Enable Antimalware Scan Interface (AMSI) integration for SharePoint web applications Configure AMSI Request Body Scan Mode to Full Mode where operationally feasible Restrict or eliminate direct Internet exposure of SharePoint servers whenever possible Limit access to SharePoint Central Administration and management interfaces Monitor for Indicators of Compromise: Organizations should closely monitor SharePoint environments for: Unexpected privilege escalation activity Unauthorized authentication attempts Suspicious IIS machine key access Evidence of deserialization attacks or web shell deployment Microsoft Defender and AMSI detections related to SharePoint exploitation activity Important note: Microsoft SharePoint Enterprise Server 2016 Footnote 11 and Server 2019 Footnote 12 are end of life as of 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 13 . 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 < 16.0.5556.1005; Microsoft SharePoint Server 2019: 16.0.0 < 16.0.10417.20153; Microsoft SharePoint Server Subscription Edition: 16.0.0 < 16.0.19725.20384 · Fixed: An authoritative update reference is available, but the fixed version is not recorded in the structured CVE fields. Check the linked vendor advisory for the applicable release.
- Vendor guidanceAuthoritative vendor guidance changed: added remediation: msrc.microsoft.com/CVE-2026-58644; removed remediation: cyber.gc.ca/al26-017-critical-vulnerabilities-impacting-microsoft-sharepoint-server-cve-2026-56164-cve-2026-55040-cve-2026-58644.secure@microsoft.com ↗
- Before
- patch: msrc.microsoft.com/CVE-2026-58644 · remediation: cyber.gc.ca/al26-017-critical-vulnerabilities-impacting-microsoft-sharepoint-server-cve-2026-56164-cve-2026-55040-cve-2026-58644
- After
- patch: msrc.microsoft.com/CVE-2026-58644 · remediation: msrc.microsoft.com/CVE-2026-58644
- Affected versionsThe structured affected or fixed version information changed.CISA KEV ↗
- Before
- Microsoft SharePoint Enterprise Server 2016: 16.0.0 < 16.0.5556.1005; Microsoft SharePoint Server 2019: 16.0.0 < 16.0.10417.20153; Microsoft SharePoint Server Subscription Edition: 16.0.0 < 16.0.19725.20384 · 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 16.0.5561.1001 16.0.5561.1001 Microsoft SharePoint Server 2019 16.0.0 before 16.0.10417.20175 16.0.10417.20175 Microsoft SharePoint Server Subscription Edition 16.0.0 before 16.0.19725.20434 16.0.19725.20434 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 to all affected SharePoint Servers including (Subscription Edition, 2019, and 2016) Monitor SharePoint servers for suspicious activity, including unusual requests, web shells, malicious processes, unauthorized access attempts, and machine key theft indicators Harden SharePoint Deployments: Enable Antimalware Scan Interface (AMSI) integration for SharePoint web applications Configure AMSI Request Body Scan Mode to Full Mode where operationally feasible Restrict or eliminate direct Internet exposure of SharePoint servers whenever possible Limit access to SharePoint Central Administration and management interfaces Monitor for Indicators of Compromise: Organizations should closely monitor SharePoint environments for: Unexpected privilege escalation activity Unauthorized authentication attempts Suspicious IIS machine key access Evidence of deserialization attacks or web shell deployment Microsoft Defender and AMSI detections related to SharePoint exploitation activity Important note: Microsoft SharePoint Enterprise Server 2016 Footnote 11 and Server 2019 Footnote 12 are end of life as of 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 13 . 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 < 16.0.5556.1005; Microsoft SharePoint Server 2019: 16.0.0 < 16.0.10417.20153; Microsoft SharePoint Server Subscription Edition: 16.0.0 < 16.0.19725.20384 · Fixed: An authoritative update reference is available, but the fixed version is not recorded in the structured CVE fields. Check the linked vendor advisory for the applicable release.
- Affected versionsThe structured affected or fixed version information changed.CNA ↗
- Before
- 16.0.0 < 16.0.5556.1005; 16.0.0 < 16.0.10417.20153; 16.0.0 < 16.0.19725.20384 · Fixed: An authoritative update reference is available, but the fixed version is not recorded in the structured CVE fields. Check the linked vendor advisory for the applicable release.
- After
- Microsoft SharePoint Enterprise Server 2016: 16.0.0 < 16.0.5556.1005; Microsoft SharePoint Server 2019: 16.0.0 < 16.0.10417.20153; Microsoft SharePoint Server Subscription Edition: 16.0.0 < 16.0.19725.20384 · Fixed: An authoritative update reference is available, but the fixed version is not recorded in the structured CVE fields. Check the linked vendor advisory for the applicable release.
- BlackTree coverageBlackTree article coverage changed from no BlackTree article to 1 BlackTree article.BlackTree editorial ↗
- Before
- no BlackTree article
- After
- 1 BlackTree article
- Affected versionsThe structured affected or fixed version information changed.Canadian Centre for Cyber Security ↗
- Before
- Microsoft SharePoint Enterprise Server 2016: 16.0.0 < 16.0.5556.1005; Microsoft SharePoint Server 2019: 16.0.0 < 16.0.10417.20153; Microsoft SharePoint Server Subscription Edition: 16.0.0 < 16.0.19725.20384 · Fixed: An authoritative update reference is available, but the fixed version is not recorded in the structured CVE fields. Check the linked vendor advisory for the applicable release.
- After
- Microsoft SharePoint Enterprise Server 2016: 16.0.0 < 16.0.5556.1005; Microsoft SharePoint Server 2019: 16.0.0 < 16.0.10417.20153; Microsoft SharePoint Server Subscription Edition: 16.0.0 < 16.0.19725.20384 · 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 16.0.5561.1001 16.0.5561.1001 Microsoft SharePoint Server 2019 16.0.0 before 16.0.10417.20175 16.0.10417.20175 Microsoft SharePoint Server Subscription Edition 16.0.0 before 16.0.19725.20434 16.0.19725.20434 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 to all affected SharePoint Servers including (Subscription Edition, 2019, and 2016) Monitor SharePoint servers for suspicious activity, including unusual requests, web shells, malicious processes, unauthorized access attempts, and machine key theft indicators Harden SharePoint Deployments: Enable Antimalware Scan Interface (AMSI) integration for SharePoint web applications Configure AMSI Request Body Scan Mode to Full Mode where operationally feasible Restrict or eliminate direct Internet exposure of SharePoint servers whenever possible Limit access to SharePoint Central Administration and management interfaces Monitor for Indicators of Compromise: Organizations should closely monitor SharePoint environments for: Unexpected privilege escalation activity Unauthorized authentication attempts Suspicious IIS machine key access Evidence of deserialization attacks or web shell deployment Microsoft Defender and AMSI detections related to SharePoint exploitation activity Important note: Microsoft SharePoint Enterprise Server 2016 Footnote 11 and Server 2019 Footnote 12 are end of life as of 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 13 . 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 .
CVE published
Added to CISA KEV
Fixed release or patch reference recorded
Fixed release recorded from official guidance
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.