CVE-2025-21298 — Windows (OLE Component)¶

Key facts

CVE-2025-21298 (Microsoft) is a Critical vulnerability: Windows (OLE Component). This entry ships ready-to-deploy detection and prevention rules (Snort, YARA, Nginx, Apache) plus a detection-only PoC and a Docker test lab.


CVE	CVE-2025-21298
Severity	Critical
Vendor	Microsoft
Product	Windows (OLE Component)
Detection / prevention	Snort, YARA, Nginx, Apache
PoC	poc.py
Source	2025/CVE-2025-21298/

Details¶

CVE-2025-21298 (Microsoft) is a Critical vulnerability: Windows (OLE Component). This entry ships a detection-only proof-of-concept (PoC), a Docker test lab, and ready-to-deploy detection and prevention rules (Snort, YARA, Nginx, Apache) — see Detection and prevention below. Source: NVD record.

Windows OLE Remote Code Execution Vulnerability¶

Overview¶

Field	Value
CVE ID	CVE-2025-21298
Severity	Critical (CVSS 9.8)
Vendor	Microsoft
Product	Windows (OLE Component)
Vulnerability Type	Remote Code Execution
Exploitation	Remote, User Interaction Required

Description¶

A critical vulnerability exists in Windows OLE (Object Linking and Embedding) that allows remote code execution when a user views specially crafted email content in Microsoft Outlook or previews malicious files. The vulnerability can be exploited via email preview without requiring the user to open attachments.

Affected Versions¶

Windows 10 (all supported versions)
Windows 11 (all supported versions)
Windows Server 2016, 2019, 2022

Impact¶

Remote Code Execution
System compromise via email preview
No user click required (preview pane exploitation)
Potential for wormable attacks

¶

Verification Process¶

The PoC uses a multi-stage verification approach:

Step 1: Product/Version Detection (Passive)¶

[*] Query target endpoint
[*] Detect product signatures and extract version
[*] Check if version is in vulnerable range

Step 2: Active Vulnerability Testing¶

Method	Description	Detection
Error-based	Tests for error messages indicating vulnerability	Error indicators in response
Timing-based	Measures response delay with payload	Response time significantly longer
Response-based	Checks for expected patterns in response	Vulnerability indicators present

Verification Flow¶

┌─────────────────────────────────────────────────────────────┐
│                    Product Detection                         │
│  Query target → Detect product/version                      │
│  Check if version in vulnerable range                       │
└─────────────────────────────────────────────────────────────┘
                              ↓
┌─────────────────────────────────────────────────────────────┐
│               Active Vulnerability Testing                   │
│                                                              │
│  1. Error-based Test                                         │
│     └─ Send payload → Check for error indicators            │
│     └─ If error found → CONFIRMED VULNERABLE                │
│                                                              │
│  2. Timing-based Test                                        │
│     └─ Send delay payload → Measure response time           │
│     └─ If delayed → CONFIRMED VULNERABLE                    │
│                                                              │
│  3. Response-based Test                                      │
│     └─ Send payload → Check response content                │
│     └─ If pattern matches → CONFIRMED VULNERABLE            │
└─────────────────────────────────────────────────────────────┘

Usage¶

# Full vulnerability check (version + active testing)
python3 poc.py -t https://target.com -c

# Version-only check (passive, no payloads sent)
python3 poc.py -t https://target.com -c --version-only

References¶

https://nvd.nist.gov/vuln/detail/CVE-2025-21298
https://msrc.microsoft.com/update-guide/

Disclaimer¶

This POC is for educational and authorized security testing only.

Detection and prevention¶

Ready-to-deploy defensive rules for CVE-2025-21298, for authorized testing and blue-team detection engineering:

Snort IDS signature — prevention/snort.rules
YARA detection rule — prevention/yara.yar
Nginx mitigation — prevention/nginx.conf
Apache HTTPD mitigation — prevention/httpd.conf
Detection-only PoC — poc.py
Rule notes — prevention/README.md

References: NVD — CVE-2025-21298 · full write-up on the searchable site

Detection & prevention rules¶

Snort IDS signatureYARA detection ruleNginx mitigationApache HTTPD mitigation

# CVE-2025-21298 - Windows OLE RCE Snort Detection Rules
# Severity: Critical (CVSS 9.8)

# Detect RTF files in email
alert tcp $EXTERNAL_NET any -> $HOME_NET $SMTP_PORTS (
    msg:"CVE-2025-21298 RTF File in Email";
    flow:to_server,established;
    content:"Content-Type|3a|"; nocase;
    content:"application/rtf"; nocase; distance:0;
    classtype:attempted-admin;
    sid:2025212981;
    rev:1;
    metadata:cve CVE-2025-21298, severity critical;
)

# Detect OLE object header in email
alert tcp $EXTERNAL_NET any -> $HOME_NET $SMTP_PORTS (
    msg:"CVE-2025-21298 OLE Object in Email";
    flow:to_server,established;
    content:"|D0 CF 11 E0 A1 B1 1A E1|";
    classtype:attempted-admin;
    sid:2025212982;
    rev:1;
    metadata:cve CVE-2025-21298, severity critical;
)

# Detect malicious RTF OLE embedding
alert tcp $EXTERNAL_NET any -> $HOME_NET $SMTP_PORTS (
    msg:"CVE-2025-21298 Malicious RTF OLE Object";
    flow:to_server,established;
    content:"{\\rtf"; nocase;
    content:"\\object"; nocase; distance:0;
    content:"\\objocx"; nocase; distance:0;
    classtype:attempted-admin;
    sid:2025212983;
    rev:1;
    metadata:cve CVE-2025-21298, severity critical;
)

# Detect RTF file download
alert tcp $HOME_NET any -> $EXTERNAL_NET $HTTP_PORTS (
    msg:"CVE-2025-21298 RTF File Download";
    flow:to_client,established;
    content:"Content-Type|3a|"; nocase;
    content:"application/rtf"; nocase;
    classtype:policy-violation;
    sid:2025212984;
    rev:1;
    metadata:cve CVE-2025-21298, severity medium;
)

# Detect potential OLE exploitation response
alert tcp any any -> $HOME_NET any (
    msg:"CVE-2025-21298 Potential OLE Exploitation";
    content:"|D0 CF 11 E0|";
    content:"Package"; distance:0; within:200;
    classtype:attempted-admin;
    sid:2025212985;
    rev:1;
    metadata:cve CVE-2025-21298, severity critical;
)

:material-file-download: prevention/snort.rules

/*
 * CVE-2025-21298 - Windows OLE RCE YARA Detection Rules
 * Severity: Critical (CVSS 9.8)
 */

rule CVE_2025_21298_Malicious_RTF {
    meta:
        description = "Detects malicious RTF files exploiting CVE-2025-21298"
        author = "Security Research"
        date = "2025-01-14"
        cve = "CVE-2025-21298"
        severity = "critical"

    strings:
        // RTF header
        $rtf_header = "{\\rtf1" ascii

        // OLE object embedding
        $ole1 = "\\object" ascii nocase
        $ole2 = "\\objocx" ascii nocase
        $ole3 = "\\objemb" ascii nocase
        $ole4 = "\\objdata" ascii nocase

        // Suspicious OLE classes
        $class1 = "Package" ascii wide
        $class2 = "OLE2Link" ascii wide
        $class3 = "Equation.3" ascii wide

        // Malicious patterns
        $mal1 = /\\bin[0-9]{5,}/ ascii
        $mal2 = "\\*\\objclass" ascii

    condition:
        $rtf_header at 0 and
        (any of ($ole*)) and
        (any of ($class*) or any of ($mal*))
}

rule CVE_2025_21298_OLE_Header {
    meta:
        description = "Detects suspicious OLE compound files"
        author = "Security Research"
        date = "2025-01-14"
        cve = "CVE-2025-21298"
        severity = "high"

    strings:
        // OLE file header
        $ole_header = { D0 CF 11 E0 A1 B1 1A E1 }

        // Malicious stream indicators
        $stream1 = "\\x01Ole" ascii
        $stream2 = "\\x01CompObj" ascii
        $stream3 = "Package" ascii wide

        // Shellcode patterns
        $shell1 = { 90 90 90 90 }  // NOP sled
        $shell2 = { FC E8 }        // Common shellcode start

    condition:
        $ole_header at 0 and
        (any of ($stream*) or any of ($shell*))
}

rule CVE_2025_21298_Email_Payload {
    meta:
        description = "Detects email payloads for CVE-2025-21298"
        author = "Security Research"
        date = "2025-01-14"
        cve = "CVE-2025-21298"
        severity = "critical"

    strings:
        // Email headers
        $email1 = "Content-Type:" ascii nocase
        $email2 = "application/rtf" ascii nocase
        $email3 = "text/rtf" ascii nocase

        // RTF content
        $rtf = "{\\rtf" ascii

        // OLE indicators
        $ole1 = "\\object" ascii
        $ole2 = "objdata" ascii

        // Base64 encoded OLE header
        $b64_ole = "0M8R4KGxGuE" ascii

    condition:
        any of ($email*) and ($rtf or $b64_ole) and any of ($ole*)
}

rule CVE_2025_21298_Outlook_Exploit {
    meta:
        description = "Detects Outlook-specific exploitation of CVE-2025-21298"
        author = "Security Research"
        date = "2025-01-14"
        cve = "CVE-2025-21298"
        severity = "critical"

    strings:
        // Calendar/meeting request patterns
        $cal1 = "BEGIN:VCALENDAR" ascii
        $cal2 = "METHOD:REQUEST" ascii
        $cal3 = "X-ALT-DESC" ascii

        // HTML with OLE
        $html1 = "<object" ascii nocase
        $html2 = "classid=" ascii nocase
        $html3 = "application/x-oleobject" ascii nocase

        // RTF in alternative body
        $rtf = "{\\rtf" ascii

    condition:
        (any of ($cal*) and $rtf) or
        (2 of ($html*))
}

:material-file-download: prevention/yara.yar

# CVE-2025-21298 - Windows OLE Prevention Rules for Nginx
# Use for email gateways and web proxies

# Block RTF file uploads
location /upload {
    # Block RTF and related file types
    if ($content_type ~* "(application/rtf|text/rtf|application/x-rtf)") {
        return 415;
    }

    # Check file extension
    if ($request_uri ~* "\.(rtf|doc|docx|ole)$") {
        # Log and inspect
        access_log /var/log/nginx/ole-uploads.log;
    }

    client_max_body_size 25M;
}

# Block OLE object content types in responses
location / {
    # Proxy response filtering (requires additional module)
    # Block potentially malicious content types

    # Add security headers
    add_header X-Content-Type-Options "nosniff" always;
    add_header X-Download-Options "noopen" always;
}

# Email attachment proxy rules
location /mail/attachments/ {
    # Log all attachment access
    access_log /var/log/nginx/mail-attachments.log;

    # Block known dangerous types
    if ($upstream_http_content_type ~* "(application/rtf|application/oleobject)") {
        return 403;
    }
}

:material-file-download: prevention/nginx.conf

# CVE-2025-21298 - Windows OLE Prevention Rules for Apache HTTPD

# Block RTF file uploads
<LocationMatch "^/upload">
    # Block RTF content type
    SetEnvIfNoCase Content-Type "application/rtf" block_rtf=1
    SetEnvIfNoCase Content-Type "text/rtf" block_rtf=1

    <If "env('block_rtf') == '1'">
        Require all denied
    </If>
</LocationMatch>

# ModSecurity Rules
<IfModule mod_security2.c>
    # Block RTF file uploads
    SecRule FILES_NAMES "@rx \\.rtf$" \
        "id:2025212981,phase:2,deny,status:403,\
        msg:'CVE-2025-21298 RTF File Upload Blocked',\
        severity:CRITICAL"

    # Block OLE object content type
    SecRule REQUEST_HEADERS:Content-Type "@rx application/(rtf|oleobject)" \
        "id:2025212982,phase:1,deny,status:415,\
        msg:'CVE-2025-21298 OLE Content Type Blocked',\
        severity:HIGH"

    # Detect RTF magic bytes in upload
    SecRule REQUEST_BODY "@rx ^\\{\\\\rtf" \
        "id:2025212983,phase:2,deny,status:403,\
        msg:'CVE-2025-21298 RTF Content Detected',\
        severity:CRITICAL"

    # Block malformed OLE headers
    SecRule REQUEST_BODY "@rx \\xD0\\xCF\\x11\\xE0" \
        "id:2025212984,phase:2,log,\
        msg:'CVE-2025-21298 OLE File Header Detected'"
</IfModule>

# Response headers
Header always set X-Content-Type-Options "nosniff"
Header always set X-Download-Options "noopen"

:material-file-download: prevention/httpd.conf

Frequently asked questions¶

What is CVE-2025-21298?¶