medium Threat analysis

Microsoft Defender CVE-2026-45498: KEV Platform DoS Exposure

CISA added Microsoft Defender CVE-2026-45498 to KEV on 2026-05-20. MSRC marks exploitation detected and gives the exact fixed Defender Antimalware Platform version 4.18.26040.7.

Published: 2026-05-26
Read time: 9 min read
Sources: 3

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Executive Summary

CISA added CVE-2026-45498 to KEV on 2026-05-20 with a due date of 2026-06-03 CISA KEV. MSRC marks exploitation detected and identifies 4.18.26040.7 as the first fixed Microsoft Defender Antimalware Platform version, with 4.18.26030.3011 as the last affected platform version reference MSRC.

Key Facts

cve: "CVE-2026-45498"
vendor: "Microsoft"
product: "Microsoft Defender Antimalware Platform"
kev_added: "2026-05-20"
kev_due: "2026-06-03"
vulnerability: "Denial of service"
cwe: ["CWE-400", "NVD-CWE-noinfo"]
affected_versions: ["4.18.26030.3011 <= platform < 4.18.26040.7"]
fixed_versions: ["4.18.26040.7"]
cvss_v31: "4.0 CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L"
msrc_exploited: true
msrc_publicly_disclosed: true

Source Confidence & Evidence Mapping

confirmed: CISA KEV lists CVE-2026-45498 as known exploited CISA KEV.
confirmed: MSRC marks exploitation detected and lists platform version 4.18.26040.7 as the first fixed version MSRC.
confirmed: NVD lists CVSS vector CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L NVD.

Impact Determination

Classification	Criteria	Required evidence	Remediation trigger	Closure condition
Confirmed compromise	Defender service crash, protection interruption, or platform failure appears on a host with affected platform version.	Platform version, host, timestamped Defender/System event, and service state.	Preserve Defender Operational and System events around the interruption.	Platform is at least 4.18.26040.7 and service-crash audit has no unexplained failures.
Presumed exposed	Defender platform is `>= 4.18.26030.3011` and `< 4.18.26040.7`.	`Get-MpComputerStatus` output or EDR inventory.	Keep the host in scope until fixed platform verification succeeds.	Version verifier returns `in_affected_range: false`.
Potentially exposed	Defender exists but platform version is missing.	Host inventory or scanner row naming Defender or CVE-2026-45498.	Collect Defender platform version.	Host resolves to confirmed compromise, presumed exposed, not exposed, or unknown.
Not exposed	Defender platform is absent, disabled in a non-exploitable state per MSRC context, or version is at least 4.18.26040.7.	Version output and Defender state.	None for this CVE.	Evidence is attached to the host record.
Unknown	Host cannot provide Defender version or event exports.	Gap statement naming missing hosts or telemetry.	Keep high-value Windows hosts in scope.	Evidence is recovered or the risk owner accepts the named gap.

Timeline

2026-05-19: MSRC publishes CVE-2026-45498 with exploitation detected MSRC.
2026-05-20: CISA adds CVE-2026-45498 to KEV with due date 2026-06-03 CISA KEV.
2026-05-20: NVD publication timestamp for CVE-2026-45498 NVD.

What Happened

This is a local Defender Antimalware Platform denial-of-service issue. The closure anchor is exact platform version 4.18.26040.7 or newer.

Technical Analysis

MSRC classifies the issue as denial of service with local attack vector and no required privileges MSRC. The useful detection path is platform version plus Defender service interruption telemetry.

Affected Assets and Blast Radius

asset_selectors:
  - "Microsoft Defender"
  - "Microsoft Defender Antimalware Platform"
  - "CVE-2026-45498"
version_selectors:
  affected_start: "4.18.26030.3011"
  fixed_platform: "4.18.26040.7"
windows_event_ids:
  - 5007
  - 5013
  - 7031
  - 7034

Indicators And Detection Selectors

cves: ["CVE-2026-45498"]
product: "Microsoft Defender Antimalware Platform"
affected_platform_range: "4.18.26030.3011 <= platform < 4.18.26040.7"
fixed_platform: "4.18.26040.7"
telemetry_selectors:
  - "MsMpEng.exe"
  - "EventID 5007"
  - "EventID 5013"
  - "EventID 7031"
  - "EventID 7034"

Detection and Hunting

Script: local repository and exported telemetry scope

#!/usr/bin/env python3
import os
import sys
import json
import subprocess
from pathlib import Path

ROOT = sys.argv[1] if len(sys.argv) > 1 else "."
LOG_ROOT = os.environ.get("LOG_ROOT", "")
OUT = Path(os.environ.get("OUT", "hp-microsoft-defender-cve-2026-45498-kev-scope"))
SINCE = "2026-05-26T00:00:00Z"
UNTIL = "2026-05-26T23:59:59Z"

PACKAGES = [
]
VERSIONS = [
]
FILES = [
]
DOMAINS = [
  "www.cisa.gov",
  "msrc.microsoft.com",
  "nvd.nist.gov",
]
URLS = [
  "https://www.cisa.gov/sites/default/files/feeds/known_exploited_vulnerabilities.json",
  "https://msrc.microsoft.com/update-guide/en-US/vulnerability/CVE-2026-45498",
  "https://nvd.nist.gov/vuln/detail/CVE-2026-45498",
]
IPS = [
]
HASHES = [
]
PROCESS_PATTERNS = [
]
NETWORK_PATTERNS = [
]

# Positive signal: repository, lockfile, artifact, process, or network telemetry contains one of the exact incident selectors above.
# Escalation: any match tied to a production build, CI run, deployed asset, or secret-bearing host moves the asset to presumed exposed.

OUT.mkdir(parents=True, exist_ok=True)
indicators_file = OUT / "indicators.txt"

# Collect unique indicators
indicators = set()
for group in [PACKAGES, VERSIONS, FILES, DOMAINS, URLS, IPS, HASHES, PROCESS_PATTERNS, NETWORK_PATTERNS]:
    for val in group:
        if val:
            indicators.add(val)

with open(indicators_file, "w") as f:
    for ind in sorted(indicators):
        f.write(ind + "\n")

print(f"[+] Written unique selectors to {indicators_file}")

# Walk local directory
print(f"[+] Scanning directory: {ROOT} for selectors...")
matches = []
exclude_dirs = {"node_modules", "vendor", "dist", ".git"}
for root, dirs, filenames in os.walk(ROOT):
    dirs[:] = [d for d in dirs if d not in exclude_dirs]
    for filename in filenames:
        filepath = Path(root) / filename
        try:
            content = filepath.read_text(errors="ignore")
            for ind in indicators:
                if ind in content:
                    matches.append(f"{filepath}: found '{ind}'")
        except Exception:
            pass

if matches:
    (OUT / "repository-indicator-matches.txt").write_text("\n".join(matches) + "\n")
    print(f"[!] Found {len(matches)} matches in codebase!")

# Optional Log Scanning
if LOG_ROOT and os.path.exists(LOG_ROOT):
    print(f"[+] Scanning telemetry log directory: {LOG_ROOT}...")
    log_matches = []
    for root, _, filenames in os.walk(LOG_ROOT):
        for filename in filenames:
            filepath = Path(root) / filename
            try:
                content = filepath.read_text(errors="ignore")
                for ind in indicators:
                    if ind in content:
                        log_matches.append(f"{filepath}: found '{ind}'")
            except Exception:
                pass
    if log_matches:
        (OUT / "exported-telemetry-indicator-matches.txt").write_text("\n".join(log_matches) + "\n")
        print(f"[!] Found {len(log_matches)} matches in logs!")

    if PACKAGES:
        registry_dir = OUT / "registry"
        registry_dir.mkdir(exist_ok=True)

print(f"[+] Wrote scope artifacts under {OUT}")

Patch, Mitigation, and Verification

$ErrorActionPreference = "Stop"
$Out = $env:OUT
if ([string]::IsNullOrWhiteSpace($Out)) { $Out = "hp-defender-cve-2026-45498-closure" }
New-Item -ItemType Directory -Force -Path $Out | Out-Null

$Cve = "CVE-2026-45498"
$FixedPlatform = [version]"4.18.26040.7"
$AffectedStart = [version]"4.18.26030.3011"
$Status = Get-MpComputerStatus
$Platform = [version]$Status.AMProductVersion
$Closed = ($Platform -ge $FixedPlatform)

[pscustomobject]@{
  cve = $Cve
  computer = $env:COMPUTERNAME
  platform_version = $Status.AMProductVersion
  affected_start = "4.18.26030.3011"
  fixed_platform = "4.18.26040.7"
  closure_state = $Closed
  msrc_source = "https://msrc.microsoft.com/update-guide/en-US/vulnerability/CVE-2026-45498"
  remediation_trigger = "Platform version below 4.18.26040.7 on a host at or above 4.18.26030.3011 keeps CVE-2026-45498 open."
} | ConvertTo-Json | Out-File -Encoding utf8 -FilePath (Join-Path $Out "defender-cve-2026-45498-closure.json")

# Remediation trigger: platform version below 4.18.26040.7 on a host at or above 4.18.26030.3011 keeps CVE-2026-45498 open.
Write-Host "wrote $Out"

Downstream Abuse Audits

Script: GitHub organization run, release, secret, and workflow audit

#!/usr/bin/env python3
import os
import sys
import json
import subprocess
from pathlib import Path

if "ORG" not in os.environ:
    print("ERROR: Set ORG environment variable to the GitHub organization to audit", file=sys.stderr)
    sys.exit(1)

ORG = os.environ["ORG"]
SINCE = "2026-05-26T00:00:00Z"
UNTIL = "2026-05-26T23:59:59Z"
OUT = Path(os.environ.get("OUT", "hp-microsoft-defender-cve-2026-45498-kev-github-audit"))

SELECTORS = [
  "www.cisa.gov",
  "msrc.microsoft.com",
  "nvd.nist.gov",
  "https://www.cisa.gov/sites/default/files/feeds/known_exploited_vulnerabilities.json",
  "https://msrc.microsoft.com/update-guide/en-US/vulnerability/CVE-2026-45498",
  "https://nvd.nist.gov/vuln/detail/CVE-2026-45498",
]

# Positive signal: a workflow run, release, secret, key, package, or workflow change overlaps the exposure window and references an incident selector.
# Remediation trigger: unauthorized post-exposure write activity or a secret-bearing run matching an incident selector requires token revocation and downstream cloud/registry review.

OUT.mkdir(parents=True, exist_ok=True)
(OUT / "runs").mkdir(exist_ok=True)
(OUT / "logs").mkdir(exist_ok=True)
(OUT / "repos").mkdir(exist_ok=True)

# 1. Write incident-selectors file
selectors_file = OUT / "incident-selectors.txt"
with open(selectors_file, "w") as sf:
    for s in SELECTORS:
        if s:
            sf.write(s + "\n")

# 2. Get list of repos
print(f"[+] Fetching repositories for organization: {ORG}")
repo_res = subprocess.run(["gh", "repo", "list", ORG, "--limit", "1000", "--json", "nameWithOwner"], capture_output=True, text=True)
if repo_res.returncode != 0:
    print(f"[-] Failed to fetch repos: {repo_res.stderr}", file=sys.stderr)
    sys.exit(1)

repos = [r["nameWithOwner"] for r in json.loads(repo_res.stdout)]

for repo in repos:
    safe_repo = repo.replace("/", "__")
    print(f"[+] Auditing repository: {repo}")

    # Check runs in the window
    runs_res = subprocess.run([
        "gh", "api", f"/repos/{repo}/actions/runs",
        "-f", "per_page=100",
        "-f", f"created=>={SINCE}",
        "--paginate"
    ], capture_output=True, text=True)

    if runs_res.returncode == 0:
        try:
            all_runs = json.loads(runs_res.stdout).get("workflow_runs", [])
            filtered_runs = [r for r in all_runs if r["created_at"] <= UNTIL]

            if filtered_runs:
                with open(OUT / "runs" / f"{safe_repo}-runs.jsonl", "w") as rf:
                    for run in filtered_runs:
                        rf.write(json.dumps(run) + "\n")

                        # Fetch log dynamically
                        run_id = str(run["id"])
                        log_res = subprocess.run(["gh", "run", "view", run_id, "--repo", repo, "--log"], capture_output=True, text=True)
                        if log_res.returncode == 0:
                            (OUT / "logs" / f"{safe_repo}-{run_id}.log").write_text(log_res.stdout)

                        # Fetch details
                        view_res = subprocess.run(["gh", "run", "view", run_id, "--repo", repo, "--json", "databaseId,workflowName,headSha,event,createdAt,jobs"], capture_output=True, text=True)
                        if view_res.returncode == 0:
                            (OUT / "runs" / f"{safe_repo}-{run_id}.json").write_text(view_res.stdout)
        except Exception as e:
            print(f"[-] Error parsing runs for {repo}: {e}")

    # Check releases in window
    subprocess.run(["gh", "api", f"/repos/{repo}/releases", "-f", "per_page=100", "--paginate"], capture_output=True)
    # Check repo secrets updated in window
    subprocess.run(["gh", "api", f"/repos/{repo}/actions/secrets", "-f", "per_page=100", "--paginate"], capture_output=True)
    # Check deploy keys
    subprocess.run(["gh", "api", f"/repos/{repo}/keys", "-f", "per_page=100", "--paginate"], capture_output=True)

# Scan output directory for any indicator selector matches
print("[+] Scanning gathered telemetry for indicator matches...")
subprocess.run(["rg", "-n", "--hidden", "--fixed-strings", "-f", str(selectors_file), str(OUT)], capture_output=False)

print(f"[+] Wrote GitHub audit artifacts under {OUT}")

Script: cloud OIDC and deployment credential follow-on audit

#!/usr/bin/env python3
import os
import json
import subprocess
from pathlib import Path

SINCE = "2026-05-26T00:00:00Z"
UNTIL = "2026-05-26T23:59:59Z"
OUT = Path(os.environ.get("OUT", "hp-microsoft-defender-cve-2026-45498-kev-cloud-audit"))
AWS_REGIONS = os.environ.get("AWS_REGIONS", "us-east-1").split(",")

# Positive signal: token exchange or privileged write activity occurs in the exposure window from GitHub, CI/CD, package registry, or deployment automation identity.
# Remediation trigger: unexpected write, deploy, IAM, secret, or registry activity tied to an exposed CI/CD path requires trust-policy disablement and credential rotation.

OUT.mkdir(parents=True, exist_ok=True)

# 1. AWS CloudTrail Audit
print("[+] Querying AWS CloudTrail for Web Identity token exchanges...")
aws_events = []
for region in AWS_REGIONS:
    res = subprocess.run([
        "aws", "cloudtrail", "lookup-events",
        "--region", region,
        "--start-time", SINCE,
        "--end-time", UNTIL,
        "--lookup-attributes", "AttributeKey=EventName,AttributeValue=AssumeRoleWithWebIdentity",
        "--output", "json"
    ], capture_output=True, text=True)

    if res.returncode == 0:
        try:
            events = json.loads(res.stdout).get("Events", [])
            for event in events:
                ct = json.loads(event.get("CloudTrailEvent", "{}"))
                ct["region"] = region
                aws_events.append(ct)
        except Exception as e:
            print(f"[-] Error parsing AWS CloudTrail events: {e}")

if aws_events:
    with open(OUT / "aws-assume-role-with-web-identity.jsonl", "w") as f:
        for ev in aws_events:
            f.write(json.dumps(ev) + "\n")

    # Audit follow-on events for returned access keys
    for ev in aws_events:
        access_key = ev.get("responseElements", {}).get("credentials", {}).get("accessKeyId")
        region = ev.get("region", "us-east-1")
        if access_key:
            print(f"[+] Enumerating AWS events for AccessKey: {access_key}")
            f_res = subprocess.run([
                "aws", "cloudtrail", "lookup-events",
                "--region", region,
                "--start-time", SINCE,
                "--end-time", UNTIL,
                "--lookup-attributes", f"AttributeKey=AccessKeyId,AttributeValue={access_key}",
                "--output", "json"
            ], capture_output=True, text=True)
            if f_res.returncode == 0:
                try:
                    f_events = json.loads(f_res.stdout).get("Events", [])
                    with open(OUT / "aws-follow-on-api-calls.jsonl", "a") as ff:
                        for fe in f_events:
                            ff.write(fe.get("CloudTrailEvent", "{}") + "\n")
                except Exception as e:
                    print(f"[-] Error writing follow-on events: {e}")

# 2. Azure Activity Log Audit
print("[+] Querying Azure activity logs...")
az_res = subprocess.run([
    "az", "monitor", "activity-log", "list",
    "--start-time", SINCE,
    "--end-time", UNTIL,
    "--query", "[?contains(operationName.value, 'write') || contains(operationName.value, 'delete') || contains(operationName.value, 'Microsoft.ManagedIdentity')]",
    "-o", "json"
], capture_output=True, text=True)

if az_res.returncode == 0:
    (OUT / "azure-write-delete-activity.json").write_text(az_res.stdout)

# 3. GCP Logging Audit
print("[+] Querying GCP Cloud Logging...")
gcp_filter = f'timestamp>="{SINCE}" AND timestamp<="{UNTIL}" AND (protoPayload.methodName="google.sts.v1.SecurityTokenService.ExchangeToken" OR protoPayload.methodName:"GenerateAccessToken" OR protoPayload.methodName:"CreateServiceAccountKey" OR protoPayload.methodName:"SetIamPolicy")'
gcp_res = subprocess.run([
    "gcloud", "logging", "read", gcp_filter,
    "--format", "json"
], capture_output=True, text=True)

if gcp_res.returncode == 0:
    (OUT / "gcp-token-and-iam-activity.json").write_text(gcp_res.stdout)

print(f"[+] Wrote cloud audit artifacts under {OUT}")

Script: registry metadata and artifact audit

#!/usr/bin/env python3
import os
import json
import subprocess
from pathlib import Path

SINCE = "2026-05-26T00:00:00Z"
OUT = Path(os.environ.get("OUT", "hp-microsoft-defender-cve-2026-45498-kev-registry-audit"))
PACKAGES = [
]
VERSIONS = [
]

# Positive signal: workflow files or extensions reference the affected action/extension names or versions.
# Remediation trigger: exposed secrets or OIDC federation policies must be immediately rotated.

OUT.mkdir(parents=True, exist_ok=True)

with open(OUT / "affected-versions.txt", "w") as av:
    for version in VERSIONS:
        if version:
            av.write(version + "\n")

    # 1. Search local workspace files for the affected actions/extensions
    print("[+] Scanning workspace workflows for selectors...")
    for file in Path(".").glob(".github/workflows/**/*.yml"):
        subprocess.run(["rg", "-n", "--hidden", "--fixed-strings", "-f", str(OUT / "affected-versions.txt"), str(file)])

    # 2. HOW TO ROTATE EXPOSED GITHUB ACTIONS SECRETS:
    # Overwrite compromised secrets with newly generated credentials:
    # subprocess.run(["gh", "secret", "set", "COMPROMISED_SECRET_NAME", "--body", "my-new-secret-value", "--repo", "my-org/my-repo"])
    # For organization-level secrets:
    # subprocess.run(["gh", "secret", "set", "COMPROMISED_SECRET_NAME", "--org", "my-org", "--visibility", "private"])
    # Revoke compromised OIDC federated trust credentials in AWS/GCP and redeploy the IAM trust policy:
    # subprocess.run(["aws", "iam", "update-assume-role-policy", "--role-name", "my-role-name", "--policy-document", "file://new-clean-trust-policy.json"])

print(f"[+] Wrote registry audit artifacts under {OUT}")