CVE-2023-50969

Executive Summary

CVE-2023-50969 identifies a security bypass vulnerability in Thales Imperva SecureSphere WAF version 14.7.0.40. The flaw allows remote attackers to bypass WAF rules by sending a crafted POST request. This is distinct from CVE-2021-45468, which targeted a similar bypass vector. The vulnerability has a CVSS score of 0.0 (likely unassigned or placeholder), but the EPSS score is also 0.0%, indicating low exploitation probability at this time. No public proof-of-concept or exploit code has been released. The vendor patch status is unknown, leaving affected systems exposed.

This vulnerability is not related to a WordPress plugin or component; it is a network security appliance (WAF) issue.

Supply Chain & Package Security

This vulnerability does not affect NPM, PyPI, Go, or Ruby packages. It is a proprietary hardware/software appliance from Thales (Imperva).

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (Unassigned)
• CVSS Vector: UNKNOWN
• Attack Vector (AV): Network (likely)
• Attack Complexity (AC): Low (likely)
• Privileges Required (PR): None (likely)
• User Interaction (UI): None (likely)
• Scope (S): Unchanged (likely)
• Confidentiality (C): High (likely, as WAF bypass can expose protected data)
• Integrity (I): High (likely, as rules can be bypassed)
• Availability (A): Low (likely, not directly affecting availability)
• Threat Level: Medium (due to lack of patch and potential for bypass)

Deep Dive & Mechanics

The vulnerability resides in the request parsing logic of the Imperva SecureSphere WAF. By crafting a specific POST request, an attacker can cause the WAF to misinterpret the request structure, thereby bypassing security rules that would normally block malicious payloads (e.g., SQL injection, XSS, path traversal). The exact mechanism is not publicly documented, but it likely involves HTTP request smuggling, parameter pollution, or encoding tricks that the WAF fails to normalize correctly.

The WAF version 14.7.0.40 is affected. The vulnerability is distinct from CVE-2021-45468, which was a similar bypass but likely exploited a different parsing flaw.

Vulnerable vs. Patched Code

No patch is available. The vulnerable code is proprietary and not publicly accessible. The following is a conceptual example of how a bypass might work:

Vulnerable (WAF rule bypass):

POST /api/login HTTP/1.1
Host: target.com
Content-Type: application/x-www-form-urlencoded
Content-Length: 45

username=admin&password=123456&%00admin=true

The WAF might fail to decode the null byte (%00) and treat the parameter as admin=true, bypassing authentication checks.

Patched (expected behavior):

POST /api/login HTTP/1.1
Host: target.com
Content-Type: application/x-www-form-urlencoded
Content-Length: 35

username=admin&password=123456

The WAF would properly reject the null byte and enforce rules.

Exploitation & Lab Setup

Red Team (Attacker)

1. Setup: Use a local instance of Imperva SecureSphere WAF 14.7.0.40 (if available) or a cloud-based test environment.
2. Craft Payload: Create a POST request with a malicious payload that would normally be blocked (e.g., SQL injection: ' OR 1=1--).
3. Bypass Technique: Encode the payload using HTTP parameter pollution or chunked transfer encoding to confuse the WAF.
4. Execute: Send the crafted request using tools like Burp Suite, curl, or custom Python scripts.

Example curl command:

curl -X POST http://target.com/vulnerable-endpoint \
  -H "Content-Type: application/x-www-form-urlencoded" \
  -d "username=admin&password=123456&%00admin=true"

Blue Team (Defender)

1. Detection: Monitor for unusual POST requests with unexpected encoding (e.g., null bytes, double encoding, chunked transfer encoding).
2. Mitigation: If possible, upgrade to a patched version (once available). Implement additional WAF rules to block known bypass patterns.
3. Honeypot: Deploy a honeypot endpoint that mimics the vulnerable behavior to detect scanning attempts.

Indicators of Compromise (IOCs)

• Network: POST requests with unusual encoding (null bytes, double URL encoding, chunked transfer encoding).
• Logs: WAF logs showing rule bypass events or unexpected request parsing.
• Payloads: Requests containing %00, %2500, or other encoding tricks.
• Source IPs: Unknown or suspicious IP addresses sending crafted POST requests.

Detection Engineering

YARA Rule

rule CVE_2023_50969_WAF_Bypass {
    meta:
        description = "Detects crafted POST requests attempting to bypass Imperva SecureSphere WAF"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2023-50969"
    strings:
        $null_byte = "%00"
        $double_encoding = "%25"
        $chunked = "Transfer-Encoding: chunked"
    condition:
        http.method == "POST" and
        any of ($null_byte, $double_encoding, $chunked)
}

Sigma Rule

title: CVE-2023-50969 WAF Bypass Attempt
id: 8a9b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects POST requests with suspicious encoding patterns targeting Imperva SecureSphere WAF
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: imperva_securesphere
detection:
    selection:
        http_method: POST
        http_uri|contains: 
            - '%00'
            - '%2500'
            - 'Transfer-Encoding: chunked'
    condition: selection
falsepositives:
    - Legitimate use of null bytes in rare cases
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2023-50969 WAF Bypass Attempt"; flow:to_server; http_method; content:"POST"; http_uri; content:"%00"; nocase; sid:1000001; rev:1;)

Remediation & Mitigation

• Immediate: Apply any available patches from Thales. If no patch exists, consider upgrading to a newer version of SecureSphere WAF.
• Workaround: Implement additional WAF rules to block requests containing null bytes, double encoding, or chunked transfer encoding.
• Monitoring: Enable detailed logging and alerting for POST requests with unusual encoding.
• Network Segmentation: Place the WAF behind a network firewall that can filter suspicious traffic.
• Vendor Contact: Reach out to Thales support for patch status and mitigation guidance.

Valters IT
DevSecOps & Cyber Threat Intelligence