CVE-2025-26862

Executive Summary

CVE-2025-26862 is a security advisory affecting PingFederate's HTML Form Adapter when configured in non-default redirectless mode. The vulnerability allows unexpected authentication form rendering, which can enable brute force login attacks. This issue is specific to the PingFederate identity provider and does not involve any web server like Apache or Nginx. The vulnerability has a CVSS score of 0.0, indicating incomplete scoring data, but the potential impact includes unauthorized access through brute force attacks.

Supply Chain & Package Security

This vulnerability is not related to any open-source package manager (NPM, PyPI, Go, Ruby). It affects a proprietary enterprise product from PingIdentity. No supply chain implications are identified.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (Unscored)
• Attack Vector: Network (likely)
• Attack Complexity: Low (likely)
• Privileges Required: None
• User Interaction: None
• Scope: Unchanged
• Confidentiality Impact: High (potential)
• Integrity Impact: High (potential)
• Availability Impact: None

The threat level is considered High due to the potential for brute force attacks leading to account compromise.

Deep Dive & Mechanics

The vulnerability occurs in PingFederate's HTML Form Adapter when operating in redirectless mode. In this mode, the adapter is expected to handle authentication without redirecting the user to a separate login page. However, due to a flaw in the rendering logic, the authentication form may be rendered unexpectedly, allowing attackers to submit authentication attempts directly. This bypasses normal rate limiting or CAPTCHA protections that might be in place for the standard login flow.

The root cause is likely improper state management or input validation in the adapter's form rendering code. When the adapter receives a request in redirectless mode, it may incorrectly process the request and render the form, enabling repeated authentication attempts.

Vulnerable vs. Patched Code

No specific code snippets are available for this vulnerability. The vulnerable component is the HTML Form Adapter in PingFederate when configured with redirectless=true. The patched version would likely include additional checks to ensure the form is only rendered when appropriate, and rate limiting or CAPTCHA enforcement is applied.

Exploitation & Lab Setup

Red Team

To simulate exploitation, set up a PingFederate instance with the HTML Form Adapter configured in redirectless mode. Use a tool like Burp Suite or a custom script to send repeated authentication requests to the adapter endpoint.

import requests

target_url = "https://target-pingfederate/pf/htmlFormAdapter"
payload = {
    "username": "admin",
    "password": "password123"
}

for i in range(1000):
    response = requests.post(target_url, data=payload)
    if response.status_code == 200:
        print(f"Attempt {i}: Success")
    else:
        print(f"Attempt {i}: Failed")

Blue Team

Monitor for excessive authentication attempts to the HTML Form Adapter endpoint. Implement rate limiting and CAPTCHA for redirectless mode. Review logs for repeated failed login attempts.

Indicators of Compromise (IOCs)

• Network: Repeated POST requests to /pf/htmlFormAdapter with authentication parameters.
• Logs: High volume of failed authentication events in PingFederate audit logs.
• System: Unusual CPU or memory usage on PingFederate server due to brute force attempts.

Detection Engineering

YARA Rule

rule Detect_PingFederate_BruteForce {
    meta:
        description = "Detects brute force attempts against PingFederate HTML Form Adapter"
        author = "Valters IT"
        date = "2025-04-01"
    strings:
        $s1 = "htmlFormAdapter" nocase
        $s2 = "redirectless" nocase
        $s3 = "username=" nocase
        $s4 = "password=" nocase
    condition:
        all of ($s*) and #s3 > 10
}

Sigma Rule

title: PingFederate Brute Force Attempt
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects multiple failed authentication attempts to PingFederate HTML Form Adapter
author: Valters IT
logsource:
    category: application
    product: pingfederate
detection:
    selection:
        event_id: "AUTH_FAILED"
        adapter: "htmlFormAdapter"
    condition: selection | count() by src_ip > 10 within 5m
falsepositives:
    - Legitimate users with forgotten passwords
level: high

Suricata Rule

alert http $EXTERNAL_NET any -> $HOME_NET any (msg:"PingFederate Brute Force Attempt"; flow:to_server; content:"POST"; http_method; content:"/pf/htmlFormAdapter"; http_uri; content:"username="; http_client_body; content:"password="; http_client_body; threshold: type both, track by_src, count 10, seconds 300; sid:1000001; rev:1;)

Remediation & Mitigation

1. Disable redirectless mode on the HTML Form Adapter if not required.
2. Implement rate limiting at the application or network level for authentication endpoints.
3. Enable CAPTCHA or multi-factor authentication (MFA) for all login attempts.
4. Monitor logs for unusual authentication patterns and set up alerts.
5. Apply vendor patches when available from PingIdentity.
6. Restrict access to the PingFederate administration interface.

Valters IT
DevSecOps & Cyber Threat Intelligence