CVE-2025-68932

Executive Summary

CVE-2025-68932 is a critical vulnerability in FreshRSS, a self-hostable RSS aggregator, affecting versions prior to 1.28.0. The vulnerability stems from the use of cryptographically weak random number generators (mt_rand() and uniqid()) to generate remember-me authentication tokens and challenge-response nonces. This weakness allows attackers to predict valid session tokens, leading to persistent session hijacking and account takeover. The remember-me tokens serve as the sole credential for the "keep me logged in" functionality, making this a severe security flaw. The vulnerability has been patched in version 1.28.0.

Supply Chain & Package Security

FreshRSS is a PHP-based application. The vulnerability is in the core authentication logic, not in a third-party package. However, administrators should ensure that all dependencies are up-to-date and that the application is not exposed to untrusted networks without proper security controls.

CVSS Breakdown & Threat Level

• CVSS Score: 9.8 (Critical)
• Attack Vector: Network (AV:N)
• Attack Complexity: Low (AC:L)
• Privileges Required: None (PR:N)
• User Interaction: None (UI:N)
• Scope: Unchanged (S:U)
• Confidentiality Impact: High (C:H)
• Integrity Impact: High (I:H)
• Availability Impact: High (A:H)

Threat Level: Critical. The vulnerability can be exploited remotely without authentication, leading to full account takeover.

Deep Dive & Mechanics

The vulnerability lies in the generation of remember-me authentication tokens and challenge-response nonces. FreshRSS uses mt_rand() and uniqid() for these purposes. mt_rand() is a Mersenne Twister PRNG that is not cryptographically secure; its output can be predicted if enough consecutive values are observed. uniqid() generates a unique identifier based on the current timestamp and is also predictable.

An attacker can:

1. Observe multiple tokens or nonces generated by the server.
2. Use these observations to predict future tokens.
3. Craft a valid remember-me token to hijack a user's session.

The remember-me token is stored in a cookie and is the sole credential for the "keep me logged in" functionality. Once an attacker predicts a valid token, they can impersonate the user indefinitely.

Vulnerable vs. Patched Code

Vulnerable Code (Pre-1.28.0):

// Vulnerable: using mt_rand() and uniqid()
$token = md5(uniqid(mt_rand(), true));

Patched Code (1.28.0+):

// Patched: using random_bytes() for cryptographically secure randomness
$token = bin2hex(random_bytes(32));

The patched version uses random_bytes() which generates cryptographically secure pseudo-random bytes, making token prediction infeasible.

Exploitation & Lab Setup

Red Team

Prerequisites:

• A FreshRSS instance running version < 1.28.0.
• Ability to observe multiple tokens (e.g., by capturing network traffic or analyzing cookies).

Exploitation Steps:

1. Token Collection: Capture multiple remember-me tokens from the FreshRSS cookie.
2. Seed Recovery: Use a tool like php_mt_seed to recover the Mersenne Twister seed from the observed tokens.
3. Token Prediction: Generate future tokens using the recovered seed.
4. Session Hijacking: Set the predicted token in your browser's cookie to hijack the user's session.

Example (Conceptual):

# Capture tokens from network traffic
# Use a tool to recover the mt_rand() seed
# Predict the next token
# Set the cookie and access the application

Blue Team

Detection:

• Monitor for multiple failed login attempts followed by successful session hijacking.
• Look for anomalies in token generation patterns.
• Use the detection rules provided below.

Mitigation:

• Immediately upgrade to FreshRSS version 1.28.0 or later.
• Invalidate all existing remember-me tokens after patching.
• Implement additional authentication factors (e.g., 2FA) if possible.

Indicators of Compromise (IOCs)

• Network: Unusual patterns in FreshRSS cookie values (e.g., tokens that are predictable or match a known seed).
• Logs: Multiple failed login attempts from the same IP, followed by a successful session hijack.
• File: Presence of exploit scripts or tools like php_mt_seed on the server.

Detection Engineering

YARA Rule

rule CVE_2025_68932_FreshRSS_Weak_RNG {
    meta:
        description = "Detects FreshRSS versions using weak random number generators"
        author = "Valters IT"
        date = "2025-01-01"
        reference = "CVE-2025-68932"
    strings:
        $weak_rng1 = "mt_rand" nocase
        $weak_rng2 = "uniqid" nocase
        $token_gen = "remember-me" nocase
    condition:
        all of ($weak_rng*) and $token_gen
}

Sigma Rule

title: CVE-2025-68932 - FreshRSS Weak Random Number Generator
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects attempts to exploit weak RNG in FreshRSS
author: Valters IT
date: 2025-01-01
logsource:
    category: webserver
    product: apache
detection:
    selection:
        c-uri|contains: "/FreshRSS"
        cs-method: "GET"
        sc-status: 200
    condition: selection
falsepositives:
    - Legitimate FreshRSS usage
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-68932 - FreshRSS Weak RNG Exploit Attempt"; flow:to_server,established; content:"FreshRSS"; http_cookie; content:"remember-me"; http_cookie; classtype:attempted-user; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Action: Upgrade to FreshRSS version 1.28.0 or later.
2. Token Invalidation: After upgrading, force all users to re-authenticate and invalidate existing remember-me tokens.
3. Network Segmentation: If possible, place FreshRSS behind a VPN or restrict access to trusted networks.
4. Monitoring: Implement the detection rules above to monitor for exploitation attempts.
5. Backup: Ensure regular backups of the FreshRSS database and configuration.

Valters IT