Microsoft SharePoint Server CVE-2026-45659: KEV exploited vulnerability

Suspected
Discovered Jul 1, 2026

Microsoft SharePoint Server contains a deserialization of untrusted data vulnerability which allows an authorized attacker to execute code over a network. CISA added it to KEV on 2026-07-01, making it an in-scope exploited-vulnerability coverage item.

1
Affected Packages
3
Observables
3
Sources

Defender Action Panel

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microsoft:sharepoint_server
Immediate action
Audit locks, CI runners, developer workstations, and credential exposure.
Hunting
Has hunting script
CVE-2026-45659
SharePoint Server
Microsoft

Analysis

Executive Summary

CVE-2026-45659 is tracked here because CISA added it to the Known Exploited Vulnerabilities catalog on 2026-07-01 with a remediation due date of 2026-07-04 [1]. The affected product is Microsoft SharePoint Server. CISA describes the vulnerability as: Microsoft SharePoint Server contains a deserialization of untrusted data vulnerability which allows an authorized attacker to execute code over a network. [1]

This is not a generic CVE roundup entry. The publish decision is based on KEV status, which is a direct source asserting known exploitation. Vendor, NVD, and product pages are used as enrichment and patch-routing sources, not as the sole proof of exploitation [2].

Key Facts

CVE: CVE-2026-45659

Vendor: Microsoft

Product: SharePoint Server

Vulnerability name: Microsoft SharePoint Server Deserialization of Untrusted Data Vulnerability

CISA KEV added: 2026-07-01

CISA remediation due date: 2026-07-04

Known ransomware campaign use: Unknown

CWE: CWE-502

Evidence Assessment

  • confirmed: CISA KEV lists CVE-2026-45659 for Microsoft SharePoint Server and states this class of entry is a known exploited vulnerability [1].
  • confirmed: CISA's required action is to apply vendor mitigations, follow BOD 26-04 risk-prioritized update handling, and discontinue use if mitigations are unavailable [1].
  • confirmed: CISA's notes point defenders to the vendor/product advisory or product page and NVD enrichment for CVE-2026-45659 [2].
  • unknown: The public KEV record does not identify specific victims, exploit timestamps, malware family, attacker infrastructure, or file hashes for this item.
  • confirmed: Affected/fixed version guidance: affected SharePoint Server Subscription Edition before 16.0.19725.20280; SharePoint Server 2016 and 2019 before the May 2026 security updates; fixed/remediated Subscription Edition 16.0.19725.20280 or later; May 2026 SharePoint Server 2016/2019 security updates per MSRC. Evidence: MSRC CVE-2026-45659 API and NVD CPE configuration..

Affected and Fixed Versions

  • Package/product coordinate: microsoft:sharepoint_server
  • Affected: SharePoint Server Subscription Edition before 16.0.19725.20280; SharePoint Server 2016 and 2019 before the May 2026 security updates
  • Fixed/remediated: Subscription Edition 16.0.19725.20280 or later; May 2026 SharePoint Server 2016/2019 security updates per MSRC
  • Version evidence: MSRC CVE-2026-45659 API and NVD CPE configuration.

Impact Determination

Analysis table
ClassificationCriteriaRequired evidenceRequired actionClosure condition
Confirmed affectedMicrosoft SharePoint Server asset is present in scope and version/fix state matches SharePoint Server Subscription Edition before 16.0.19725.20280; SharePoint Server 2016 and 2019 before the May 2026 security updates.Asset inventory, product version evidence, vendor advisory mapping, patch records, and exposure records.Apply vendor mitigation or remove exposure; preserve relevant application, web, authentication, and EDR telemetry for the exploitation window.Product is patched or retired, exposure is removed, and post-remediation scans show no vulnerable versions.
Presumed exposedProduct is present but version state, internet exposure, or mitigation status is unknown.CMDB, vulnerability scanner, WAF/proxy logs, EDR inventory, and change tickets.Treat as at-risk until version and mitigation status are proven.Inventory and patch evidence are complete.
Not observedNo asset, package, appliance, or service record references Microsoft SharePoint Server or CVE-2026-45659.Current asset inventory and vulnerability scan coverage.Keep monitoring KEV and vendor advisories.Coverage timestamp and query scope are archived.

Timeline

  • 2026-07-01: CISA adds CVE-2026-45659 to KEV and sets a remediation due date of 2026-07-04 [1].
  • 2026-07-01: This local refresh creates a conservative Halting Problems research folder and defensive scope scanner for microsoft-sharepoint-server-cve-2026-45659-kev.

Remediation Guidance

For Microsoft SharePoint Server, remediation should be tied to the vendor source listed by CISA, not a generic patch checklist. The minimum closure packet is: the vendor advisory consulted, affected assets enumerated, version or mitigation evidence recorded, internet exposure checked, logs preserved for the likely exploitation window, and compensating controls documented when patching is delayed. CISA's KEV due date of 2026-07-04 should drive urgency [1].

Open Questions

  • Are there public exploitation indicators beyond KEV status, such as IPs, hashes, paths, payload names, or campaign names?
  • Which local assets expose Microsoft SharePoint Server to untrusted networks?
  • Are product logs sufficient to distinguish scanning from successful exploitation?

IOC and Source-Selector Handling

No incident-specific attacker infrastructure, hashes, payload paths, victim list, or campaign attribution is currently published for CVE-2026-45659 in the reviewed public sources. CISA, NVD, vendor, GHSA, MSRC, Adobe, Joomla, and SimpleHelp URLs are retained as source_selectors / hunt_selectors for asset-export matching only; they are not treated as compromise IOCs.

Evidence sources to preserve

  • IIS logs for SharePoint web applications
  • SharePoint ULS logs
  • Windows Event Logs and PowerShell logs
  • EDR process/file telemetry on SharePoint servers
  • service account and authentication logs

Product-specific hunts

  • Review suspicious POST/deserialization/RCE-like request patterns to SharePoint application endpoints where safe indicators are available.
  • Search for unexpected PowerShell, cmd, w3wp child processes, new web-accessible files, or modified SharePoint layouts/features.
  • Correlate SharePoint service account activity with new persistence, credential access, or lateral movement.

Containment actions

  • Apply Microsoft security updates or isolate affected SharePoint servers from untrusted networks.
  • Preserve IIS, ULS, Windows event, EDR, and configuration snapshots before remediation.
  • Rotate impacted service account credentials if exploit success, web shell activity, or suspicious process execution is found.

Evidence Handling Requirements

  • Record all investigation and remediation times in UTC and tie them to the CISA KEV added date and due date.
  • Preserve forensic copies or snapshots before destructive cleanup when feasible.
  • Record chain of custody: collector, timestamp, source host/service, hash where applicable, storage location, and transfer history.
  • Preserve product logs, reverse proxy/WAF logs, identity/session logs, EDR telemetry, and ticket/change records for the exposure and remediation windows.
  • Record analyst owner, business owner, affected asset identifiers, and whether the asset was internet-exposed.

Strengthened Remediation and Closure Gates

  • Confirm vendor fixed version or documented retirement for every affected asset.
  • Remove or restrict untrusted exposure until the fixed version or mitigation is verified.
  • Perform a post-fix version query or vulnerability scan and archive evidence.
  • Review for exploit success, persistence, suspicious files, unauthorized sessions, credential exposure, and product-specific downstream abuse.
  • Rotate credentials/sessions/secrets when product logs, EDR, or identity telemetry indicate possible unauthorized access.
  • Monitor for product-specific suspicious activity for a documented post-recovery period.

Sources

Timeline

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Timeline
DateEventDescriptionSource
Jul 1, 2026DiscoveryDiscovery recorded for Microsoft SharePoint Server CVE-2026-45659: KEV exploited vulnerability.msrc.microsoft.com
Jul 1, 2026First seenFirst seen recorded for Microsoft SharePoint Server CVE-2026-45659: KEV exploited vulnerability.msrc.microsoft.com
Invalid DatePatch or fixPatch or fix recorded for Microsoft SharePoint Server CVE-2026-45659: KEV exploited vulnerability.msrc.microsoft.com
Jul 1, 2026Microsoft SharePoint Server CVE-2026-45659: KEV exploited vulnerabilityUnknownmsrc.microsoft.com
Jul 1, 2026DisclosureDisclosure recorded for Microsoft SharePoint Server CVE-2026-45659: KEV exploited vulnerability.msrc.microsoft.com

Affected Software

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Affected Software
PackageEcosystemVersion RangeStatusConfidenceSource
microsoft:sharepoint_serverenterprise-softwareSharePoint Server Subscription Edition before 16.0.19725.20280; SharePoint Server 2016 and 2019 before the May 2026 security updates (fixed: Subscription Edition 16.0.19725.20280 or later; May 2026 SharePoint Server 2016/2019 security updates per MSRC; evidence: MSRC CVE-2026-45659 API and NVD CPE configuration.)Malicious65%msrc.microsoft.com; nvd.nist.gov; cisa.gov

IOC Clipboard

3 IOCs
commandCVE-2026-45659
commandSharePoint Server
commandMicrosoft

Tested Hunting Scripts

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Tested Hunting Scripts
TitleLanguageDescriptionRepositorySource
Microsoft SharePoint Server asset, advisory, and telemetry selector scanPythonDo exported records reference CVE-2026-45659 or Microsoft SharePoint Server during the KEV remediation window?scripts/microsoft_sharepoint_server_cve_2026_45659_kev_scope_scan.py opens in a new tabmsrc.microsoft.com

Hunt Manifest: Microsoft SharePoint Server asset, advisory, and telemetry selector scan

Title
Microsoft SharePoint Server asset, advisory, and telemetry selector scan
Question
Do exported records reference CVE-2026-45659 or Microsoft SharePoint Server during the KEV remediation window?
Telemetry Family
Python
Repository
scripts/microsoft_sharepoint_server_cve_2026_45659_kev_scope_scan.py
Show tested hunting scriptscripts/microsoft_sharepoint_server_cve_2026_45659_kev_scope_scan.py
scripts/microsoft_sharepoint_server_cve_2026_45659_kev_scope_scan.py opens in a new tabPython
#!/usr/bin/env python3
"""Defensive scope scanner for CVE-2026-45659 (Microsoft SharePoint Server).

This script scans exported web, EDR, asset, ticket, or CMDB text/JSON/CSV data for
source and product selectors from the Halting Problems research note. It does not
contact the network and does not execute target artifacts.
"""
from __future__ import annotations

import argparse
import json
import os
from pathlib import Path

CVE_ID = 'CVE-2026-45659'
VENDOR = 'Microsoft'
PRODUCT = 'SharePoint Server'
VULNERABILITY_NAME = 'Microsoft SharePoint Server Deserialization of Untrusted Data Vulnerability'
SOURCE_DOMAINS = ['www.cisa.gov', 'msrc.microsoft.com', 'nvd.nist.gov']
AFFECTED_VERSION_RANGE = 'SharePoint Server Subscription Edition before 16.0.19725.20280; SharePoint Server 2016 and 2019 before the May 2026 security updates'
FIXED_VERSION = 'Subscription Edition 16.0.19725.20280 or later; May 2026 SharePoint Server 2016/2019 security updates per MSRC'
PACKAGE_COORDINATE = 'microsoft:sharepoint_server'
SOURCE_URLS = ['https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=cve-2026-45659', 'https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-45659', 'https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk', 'https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk', 'https://nvd.nist.gov/vuln/detail/CVE-2026-45659']
PRODUCT_MARKERS = ['CVE-2026-45659', 'Microsoft', 'SharePoint Server', 'Microsoft SharePoint Server Deserialization of Untrusted Data Vulnerability']
OUT_DEFAULT = "hp-microsoft-sharepoint-server-cve-2026-45659-kev-scope"
TEXT_EXTENSIONS = {".txt", ".log", ".json", ".jsonl", ".csv", ".tsv", ".yaml", ".yml", ".xml", ".html", ".md"}


def iter_files(root: Path):
    exclude_dirs = {".git", "node_modules", "vendor", "dist", "build", ".venv", "__pycache__"}
    for current, dirs, files in os.walk(root):
        dirs[:] = [d for d in dirs if d not in exclude_dirs]
        for name in files:
            path = Path(current) / name
            if path.suffix.lower() in TEXT_EXTENSIONS or path.stat().st_size < 2_000_000:
                yield path


def read_text(path: Path) -> str:
    try:
        return path.read_text(encoding="utf-8", errors="ignore")
    except OSError:
        return ""


def main() -> int:
    parser = argparse.ArgumentParser(description=f"Scope local exports for {CVE_ID} selectors.")
    parser.add_argument("root", nargs="?", default=".", help="Directory containing exported logs, asset inventory, tickets, or notes.")
    parser.add_argument("--out", default=OUT_DEFAULT, help="Output directory for report.json and matched files list.")
    args = parser.parse_args()

    root = Path(args.root).resolve()
    out = Path(args.out).resolve()
    out.mkdir(parents=True, exist_ok=True)

    indicators = set()
    for group in (SOURCE_DOMAINS, SOURCE_URLS, PRODUCT_MARKERS, [AFFECTED_VERSION_RANGE, FIXED_VERSION, PACKAGE_COORDINATE]):
        for val in group:
            if val:
                indicators.add(str(val))

    hits = []
    for path in iter_files(root):
        text = read_text(path)
        lower = text.lower()
        matched = sorted(ind for ind in indicators if ind.lower() in lower)
        if matched:
            hits.append({"path": str(path.relative_to(root)), "selectors": matched})

    report = {
        "event": {"cve_id": CVE_ID, "vendor": VENDOR, "product": PRODUCT, "vulnerability_name": VULNERABILITY_NAME, "package": PACKAGE_COORDINATE, "affected": AFFECTED_VERSION_RANGE, "fixed": FIXED_VERSION},
        "scan_root": str(root),
        "files_with_hits": len(hits),
        "hits": hits,
        "interpretation": {
            "positive": bool(hits),
            "positive_signal": "At least one exported record references the CVE, product, vendor advisory, CISA KEV, or NVD selector.",
            "next_steps": "Use the matched paths to scope vulnerable assets, confirm patch state, and preserve relevant web/EDR/authentication telemetry for incident review." if hits else "No local selector matches were found in the supplied export; confirm the export covers the affected product inventory and remediation window."
        }
    }
    (out / "report.json").write_text(json.dumps(report, indent=2), encoding="utf-8")
    matched_text = "\n".join(hit["path"] for hit in hits) + ("\n" if hits else "")
    (out / "matched_files.txt").write_text(matched_text, encoding="utf-8")
    print(json.dumps({"cve_id": CVE_ID, "files_with_hits": len(hits), "report": str(out / "report.json")}, indent=2))
    return 1 if False else 0


if __name__ == "__main__":
    raise SystemExit(main())

Provenance & Sources

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Provenance & Sources
SourceTypeReliabilityClaimsEvidence
msrc.microsoft.comSecurity Researcher95%1Microsoft SharePoint Server contains a deserialization of untrusted data vulnerability which allows an authorized attacker to execute code over a network. CISA added it to KEV on 2026-07-01, making it an in-scope exploited-vulnerability coverage item.
nvd.nist.govSecurity Researcher95%1Microsoft SharePoint Server contains a deserialization of untrusted data vulnerability which allows an authorized attacker to execute code over a network. CISA added it to KEV on 2026-07-01, making it an in-scope exploited-vulnerability coverage item.
cisa.govSecurity Researcher95%3Microsoft SharePoint Server contains a deserialization of untrusted data vulnerability which allows an authorized attacker to execute code over a network. CISA added it to KEV on 2026-07-01, making it an in-scope exploited-vulnerability coverage item.