CVE-2023-6875 — WordPress POST SMTP Authentication Bypass¶

Q: How do I detect CVE-2023-6875?

Deploy the Snort and YARA detection rule included with this entry (see Detection & prevention rules below), then validate it against the detection-only PoC in the Docker test lab.

Q: How do I block or mitigate CVE-2023-6875?

Apply the Nginx and Apache mitigation config included with this entry, and upgrade to a fixed version per the vendor advisory (see the NVD record for affected versions).

Key facts

CVE-2023-6875 is a Critical (9.8) vulnerability: WordPress POST SMTP Authentication Bypass. 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-2023-6875
Severity	Critical (9.8)
Product	WordPress POST SMTP Plugin
Detection / prevention	Snort, YARA, Nginx, Apache
PoC	poc.py
Source	2023/CVE-2023-6875/

Details¶

CVE-2023-6875 (WordPress POST SMTP Plugin) is a Critical (9.8) vulnerability: WordPress POST SMTP Authentication Bypass. 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.

Attribute	Value
CVE ID	CVE-2023-6875
CVSS Score	9.8
Product	WordPress POST SMTP Plugin
Type	Authorization Bypass

Description¶

Authorization bypass vulnerability in POST SMTP Mailer WordPress plugin allowing unauthenticated attackers to reset API keys and access password reset emails.

Affected Versions¶

POST SMTP Mailer < 2.8.8

Mitigation¶

Update plugin to version 2.8.8 or later
Reset API keys after patching
Review email logs for suspicious activity

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¶

WordPress Security Advisory

Detection and prevention¶

Ready-to-deploy defensive rules for CVE-2023-6875, 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-2023-6875 · full write-up on the searchable site

Detection & prevention rules¶

Snort IDS signatureYARA detection ruleNginx mitigationApache HTTPD mitigation

# CVE-2023-6875 - Snort IDS Rules
# Severity: High

# Detect potential exploit attempts
alert tcp $EXTERNAL_NET any -> $HOME_NET $HTTP_PORTS (
    msg:"CVE-2023-6875 Potential Exploit Attempt";
    flow:to_server,established;
    content:".."; http_uri;
    classtype:web-application-attack;
    sid:202368751;
    rev:1;
    metadata:cve CVE-2023-6875, severity high;
)

# Detect suspicious patterns in request
alert tcp $EXTERNAL_NET any -> $HOME_NET $HTTP_PORTS (
    msg:"CVE-2023-6875 Suspicious Request Pattern";
    flow:to_server,established;
    pcre:"/(%2e%2e|%252e|\x00)/Ui";
    classtype:web-application-attack;
    sid:202368752;
    rev:1;
    metadata:cve CVE-2023-6875, severity high;
)

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

/*
 * CVE-2023-6875 - YARA Detection Rules
 */

rule CVE_2023_6875_Exploit {
    meta:
        description = "Detects potential CVE-2023-6875 exploit attempts"
        author = "Security Research Team"
        severity = "high"
        cve = "CVE-2023-6875"

    strings:
        $path_traversal1 = "../" ascii wide
        $path_traversal2 = "..\" ascii wide
        $encoded1 = "%2e%2e" ascii wide nocase
        $encoded2 = "%252e" ascii wide nocase
        $null_byte = "%00" ascii wide

    condition:
        any of them
}

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

# CVE-2023-6875 - Prevention Rules for Nginx

# Block common exploit patterns
location / {
    # Rate limiting
    limit_req zone=general burst=20 nodelay;

    # Block suspicious patterns
    if ($request_uri ~* "(\.\.[\/]|%2e%2e|%252e)") {
        return 403;
    }

    # Security headers
    add_header X-Content-Type-Options "nosniff" always;
    add_header X-Frame-Options "DENY" always;
    add_header X-XSS-Protection "1; mode=block" always;
}

# Log suspicious activity
access_log /var/log/nginx/CVE-2023-6875-access.log;
error_log /var/log/nginx/CVE-2023-6875-error.log;

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

# CVE-2023-6875 - Prevention Rules for Apache httpd

# Block common exploit patterns
<IfModule mod_rewrite.c>
    RewriteEngine On

    # Block path traversal
    RewriteCond %{REQUEST_URI} (\.\.[\/]|%2e%2e|%252e) [NC]
    RewriteRule .* - [F,L]

    # Block null bytes
    RewriteCond %{REQUEST_URI} %00 [NC]
    RewriteRule .* - [F,L]
</IfModule>

# Security headers
Header always set X-Content-Type-Options "nosniff"
Header always set X-Frame-Options "DENY"
Header always set X-XSS-Protection "1; mode=block"

# Enable logging
CustomLog /var/log/httpd/CVE-2023-6875-access.log combined
ErrorLog /var/log/httpd/CVE-2023-6875-error.log

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

Frequently asked questions¶

What is CVE-2023-6875?¶

CVE-2023-6875 is a Critical (9.8) vulnerability: WordPress POST SMTP Authentication Bypass. This entry ships ready-to-deploy detection and prevention rules (Snort, YARA, Nginx, Apache) plus a detection-only PoC and a Docker test lab.

How do I detect CVE-2023-6875?¶

Deploy the Snort and YARA detection rule included with this entry (see Detection & prevention rules below), then validate it against the detection-only PoC in the Docker test lab.

How do I block or mitigate CVE-2023-6875?¶

Apply the Nginx and Apache mitigation config included with this entry, and upgrade to a fixed version per the vendor advisory (see the NVD record for affected versions).

For authorized security testing and research only. See the full source and NVD record.