CVE-2026-58644: Microsoft SharePoint exploited

Advisory generated from the CVE record, CISA, Exploit Observer and VEDAS: what it is, whether it is exploited, who is affected, and how to fix and detect it.

What it is

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

Description quoted from the CVE record (assigned by microsoft, published 2026-07-14).

Weakness: CWE-502: Deserialization of Untrusted Data

How it can be exploited

Exploitable over the network with low attack complexity needing no privileges and no user interaction. Impact: confidentiality high, integrity high, availability high. CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C

CISA assessment (SSVC): CISA assesses exploitation as active. Automatable: yes. Technical impact: total.

On CISA KEV since: 2026-07-16
US federal deadline: 2026-07-19
Ransomware use: Not known

Public exploit evidence (Exploit Observer)

Also known as: BDU:2026-09928, CNVD-2026-27933, EUVD-2026-43779, GHSA-q6cq-5qpf-q237

VEDAS cluster: VEDAS:BARKBOUND

Exploit Observer links 6 pieces of public exploit code or detection modules that name this CVE or one of its aliases.

Exploit code and modules (6)

Code that names this CVE. A repository can be a working exploit, a scanner, a fake or malware; read it before running anything.

Research and write-ups (2)

Research or write-up: https://avleonov.com/2026/08/07/i121-about-remote-code-execution-microsoft-sharepoint-cve202658644-vulnerability
Research or write-up: https://ptsecurity.com/research/trending-vulnerabilities/CVE-2026-58644

Vulnerability databases and vendor advisories (6)

Catalogue entries, not exploit evidence.

Vulnerability database or vendor advisory: https://euvd.enisa.europa.eu/enisa/EUVD-2026-43779
Vulnerability database or vendor advisory: https://github.com/advisories/GHSA-q6cq-5qpf-q237
Vulnerability database or vendor advisory: https://msrc.microsoft.com/update-guide/en-US/vulnerability/CVE-2026-58644
Vulnerability database or vendor advisory: https://nvd.nist.gov/vuln/detail/CVE-2026-58644
Vulnerability database or vendor advisory: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-58644
Vulnerability database or vendor advisory: https://www.cnvd.org.cn/flaw/show/CNVD-2026-27933

67 more references returned by Exploit Observer did not name this CVE or an alias, so they are left out.

VEDAS data as of 2026-11-01T17:12 UTC; fetched 2026-11-02.

Live scores

EPSS: 0.159
likely to be attacked soon
VEDAS: 0.979
strong exploit evidence
On CISA KEV: Yes, since 2026-07-16
Detection rule: Nuclei · Suricata

EPSS (chance of attack)

VEDAS (exploit evidence)

Thin horizontal line: the “likely” (EPSS 0.10) or “strong” (VEDAS 0.90) threshold. Shaded “no data” areas are periods when cve-scores did not publish.

Who is affected

Product	Affected	Not affected
Microsoft Microsoft SharePoint Enterprise Server 2016	from 16.0.0 before 16.0.5556.1005	Not stated
Microsoft Microsoft SharePoint Server 2019	from 16.0.0 before 16.0.10417.20153	Not stated
Microsoft Microsoft SharePoint Server Subscription Edition	from 16.0.0 before 16.0.19725.20384	Not stated

Version ranges exactly as the CVE record states them. “Before X” means X is the first fixed version.

Exploit Observer also maps it to: microsoft sharepoint_server, microsoft_corp microsoft_sharepoint_enterprise_server_2016, microsoft_corp microsoft_sharepoint_server_2019, microsoft_corp microsoft_sharepoint_server_subscription_edition.

How to fix it

Fixed versions stated in the CVE record: 16.0.5556.1005, 16.0.10417.20153, 16.0.19725.20384.

CISA required action: Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset’s internet exposure and ensuring adherence to BOD 26-04 patching guidelines.

Vendor guidance:

Microsoft SharePoint Remote Code Execution Vulnerability (vendor-advisory, patch)

How to detect it

Nuclei template (active check)

Microsoft SharePoint Server - WS-Federation BinaryFormatter Deserialization RCE
Microsoft SharePoint Server (2016, 2019, Subscription Edition <= 2026.3.1) contains a remote code execution vulnerability in the WS-Federation passive sign-in endpoint (/_trust/default.aspx). The SharePoint authentication module (SPFederationAuthenticationModuleV2) uses a deflate-only DeflateCookieTransform (no...

Name and description quoted from the template, written by VEDAS.

The template sends 3 requests (GET /_trust/default.aspx, POST /_trust/default.aspx, POST /_trust/default.aspx); it decides using dsl matchers. Severity in the template: critical. Marked as not yet verified against a live vulnerable target.

Run it against a host you own or are authorised to test:

bash

nuclei -u https://your-host -t CVE-2026-58644.yaml

Show the template (59 lines)

yaml

id: CVE-2026-58644

info:
  name: "Microsoft SharePoint Server - WS-Federation BinaryFormatter Deserialization RCE"
  author: vedas-arpsyndicate
  severity: critical
  description: |
    Microsoft SharePoint Server (2016, 2019, Subscription Edition <= 2026.3.1) contains a remote code execution
    vulnerability in the WS-Federation passive sign-in endpoint (/_trust/default.aspx). The SharePoint
    authentication module (SPFederationAuthenticationModuleV2) uses a deflate-only DeflateCookieTransform (no...
  reference:
    - https://www.exploit.observer/?keyword=CVE-2026-58644&match=exact
    - https://subdomain.center/?engine=ammonites&keyword=sharepointserver&match=exact
  classification:
    cvss-metrics: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
    cvss-score: 9.8
    cve-id: CVE-2026-58644
    cwe-id: CWE-502
  metadata:
    verified: false
    max-request: 3
  tags: cve,cve2026,sharepointserver,rce
http:
  - raw:
      - |
        GET /_trust/default.aspx HTTP/1.1
        Host: {{Hostname}}
        Connection: close

    matchers:
      - type: dsl
        dsl:
          - 'contains(tolower(header), "microsoftsharepointteamservices")'
        internal: true

  - raw:
      - |
        POST /_trust/default.aspx HTTP/1.1
        Host: {{Hostname}}
        Content-Type: application/x-www-form-urlencoded
        Connection: close

        wa=wsignin1.0&wctx={{url_encode(RootURL + "/")}}&wresult={{url_encode(concat('<t:RequestSecurityTokenResponse xmlns:t="http://schemas.xmlsoap.org/ws/2005/02/trust"><t:RequestedSecurityToken><sc:SecurityContextToken xmlns:sc="http://schemas.xmlsoap.org/ws/2005/02/sc"><sc:Identifier>urn:unique-id:securitycontext:vedas', rand_text_alpha(12), '</sc:Identifier><Cookie xmlns="http://schemas.microsoft.com/ws/2006/05/security">', replace_regex(javascript_response, ":.*", ""), '</Cookie></sc:SecurityContextToken></t:RequestedSecurityToken></t:RequestSecurityTokenResponse>'))}}

      - |
        POST /_trust/default.aspx HTTP/1.1
        Host: {{Hostname}}
        Content-Type: application/x-www-form-urlencoded
        Connection: close

        wa=wsignin1.0&wctx={{url_encode(RootURL + "/")}}&wresult={{url_encode(concat('<t:RequestSecurityTokenResponse xmlns:t="http://schemas.xmlsoap.org/ws/2005/02/trust"><t:RequestedSecurityToken><sc:SecurityContextToken xmlns:sc="http://schemas.xmlsoap.org/ws/2005/02/sc"><sc:Identifier>urn:unique-id:securitycontext:vedas', rand_text_alpha(12), '</sc:Identifier><Cookie xmlns="http://schemas.microsoft.com/ws/2006/05/security">', replace_regex(javascript_response, ".*:", ""), '</Cookie></sc:SecurityContextToken></t:RequestedSecurityToken></t:RequestSecurityTokenResponse>'))}}

    stop-at-first-match: true

    matchers-condition: and
    matchers:
      - type: dsl
        dsl:
          - 'contains(tolower(header), "x-vedas")'

CVE-2026-58644.yaml on GitHub

Suricata rules (network detection)

1 rule that alert on traffic matching this exploit: VEDAS CVE-2026-58644 Microsoft SharePoint Server - WS-Federation BinaryFormatter Deserialization RCE Attempt. Add them to your Suricata rule set and reload.

Show the rules

suricata

alert http $EXTERNAL_NET any -> $HTTP_SERVERS $HTTP_PORTS (msg:"VEDAS CVE-2026-58644 Microsoft SharePoint Server - WS-Federation BinaryFormatter Deserialization RCE Attempt"; flow:established,to_server; http.uri; content:"default.aspx"; nocase; http.request_body; content:"concat("; nocase; fast_pattern; classtype:web-application-attack; reference:cve,CVE-2026-58644; reference:url,https://www.exploit.observer/?keyword=CVE-2026-58644&match=exact; reference:url,https://subdomain.center/?engine=ammonites&keyword=sharepointserver&match=exact; sid:1019639; rev:1;)

CVE-2026-58644.rules on GitHub

References

Vendor advisories and patches

Microsoft SharePoint Remote Code Execution Vulnerability (vendor-advisory, patch)

Government sources

https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-58644 (government-resource)

Other databases

Where this comes from

This advisory is generated automatically by VEDAS from: CVE.org record, CISA KEV, cve-scores (EPSS and VEDAS), Exploit Observer, vedas-signatures. Text in quotes is reproduced from the source; everything else is a fixed template filled with source fields. Nothing here is written by a language model. Check the vendor advisory before acting, and read how VEDAS and Exploit Observer work, and their limits.