CVE-2026-8651

Executive Summary

CVE-2026-8651 is a low-severity (CVSS 3.7) authentication bypass vulnerability in Progress MOVEit Transfer's HTTPS module. The flaw allows an unauthenticated attacker to spoof authentication credentials, potentially gaining limited access to the system. The vulnerability affects versions prior to 2025.0.7 and from 2025.1.0 before 2025.1.3. No public exploit code or proof-of-concept is currently available, and the EPSS score is 0.0%, indicating a very low probability of exploitation in the wild. However, given MOVEit Transfer's history of critical vulnerabilities (e.g., CVE-2023-34362), this issue warrants immediate patching.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N
• Base Score: 3.7 (Low)
• Attack Vector: Network (AV:N)
• Attack Complexity: High (AC:H) – Requires specific conditions or timing to exploit.
• Privileges Required: None (PR:N)
• User Interaction: None (UI:N)
• Scope: Unchanged (S:U)
• Confidentiality Impact: Low (C:L) – Limited information disclosure possible.
• Integrity Impact: None (I:N)
• Availability Impact: None (A:N)

Threat Level: Low. The high attack complexity and lack of public exploits reduce immediate risk, but the potential for authentication bypass in a widely-used file transfer platform demands proactive patching.

Deep Dive & Mechanics

The vulnerability resides in the HTTPS module of MOVEit Transfer, which handles secure HTTP connections. The flaw is categorized as CWE-290: Authentication Bypass by Spoofing. This occurs when the application improperly validates the identity of a remote entity, allowing an attacker to impersonate a legitimate user or service.

Root Cause: The HTTPS module likely fails to properly validate TLS certificates or session tokens during the authentication handshake. An attacker could craft a malicious request with spoofed credentials (e.g., a forged JWT or manipulated session cookie) that bypasses the authentication check. The "limited" nature of the bypass suggests that only specific endpoints or actions are accessible without proper authentication.

Attack Scenario:

1. An attacker identifies a MOVEit Transfer instance running a vulnerable version.
2. The attacker sends a specially crafted HTTPS request to the server, manipulating authentication headers or tokens.
3. The server incorrectly validates the spoofed credentials, granting the attacker limited access (e.g., ability to view file metadata or initiate a transfer without full authentication).
4. The attacker may leverage this access to gather information or chain with other vulnerabilities.

Vulnerable vs. Patched Code

No specific code diff is publicly available. However, based on the CWE and vendor advisory, the patch likely involves:

• Vulnerable: The HTTPS module accepts authentication tokens without verifying their cryptographic signature or origin.
• Patched: The module now validates token signatures, checks certificate chains, and enforces strict session binding.

Hypothetical Code Example (Python-like pseudocode):

# Vulnerable code
def authenticate(request):
    token = request.headers.get('Authorization')
    # No signature verification
    user = decode_token(token)
    return user

# Patched code
def authenticate(request):
    token = request.headers.get('Authorization')
    try:
        # Verify token signature using public key
        payload = jwt.decode(token, public_key, algorithms=['RS256'])
        return payload['user']
    except jwt.InvalidTokenError:
        return None

Exploitation & Lab Setup

Red Team (Offensive):

1. Reconnaissance: Use Shodan to find exposed MOVEit Transfer instances with the dork "MOVEit Transfer".
2. Fingerprinting: Send a GET request to / and inspect the response headers for version information (e.g., X-MOVEit-Version: 2025.0.5).
3. Exploit Attempt: Since no public exploit exists, craft a custom script to test for authentication bypass:
   • Manipulate the Authorization header with a forged JWT.
   • Attempt to access protected endpoints like /api/v1/token or /human.aspx without valid credentials.

import requests

target = "https://vulnerable-moveit.com"
# Attempt to bypass authentication with a spoofed token
headers = {"Authorization": "Bearer forged_token_here"}
response = requests.get(f"{target}/api/v1/token", headers=headers, verify=False)
if response.status_code == 200:
    print("Authentication bypass successful!")
else:
    print("Bypass failed.")

Blue Team (Defensive):

1. Detection: Monitor for anomalous authentication attempts, especially repeated failures followed by a sudden success.
2. Honeypot: Deploy a decoy MOVEit Transfer instance to capture attacker behavior.
3. Network Segmentation: Ensure MOVEit Transfer is not directly exposed to the internet; use a reverse proxy with strict access controls.

Indicators of Compromise (IOCs)

• Network:
  • Unusual HTTP requests with malformed or spoofed Authorization headers.
  • Repeated attempts to access /api/v1/token or /human.aspx without prior authentication.
• Logs:
  • Authentication logs showing successful logins from unexpected IPs or without corresponding user agents.
  • Error logs indicating token validation failures.
• File System:
  • Unexpected files in the MOVEit Transfer data directory (e.g., /opt/MOVEitTransfer/Data/).

Detection Engineering

YARA Rule

rule CVE_2026_8651_MOVEit_Transfer_HTTPS_Bypass {
    meta:
        description = "Detects exploitation attempts for CVE-2026-8651 in MOVEit Transfer logs"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-8651"
    strings:
        $auth_bypass = /Authorization:\s*Bearer\s+[A-Za-z0-9_-]{20,}/ nocase
        $failed_auth = /Authentication failed for user/
        $success_auth = /User authenticated successfully/
    condition:
        $auth_bypass and #failed_auth > 5 and $success_auth
}

Sigma Rule

title: CVE-2026-8651 MOVEit Transfer Authentication Bypass Attempt
id: 8a4b3c2d-1e5f-4a7b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects potential exploitation of CVE-2026-8651 via anomalous authentication patterns
author: Valters IT
date: 2025-04-10
logsource:
    category: application
    product: moveit_transfer
detection:
    selection:
        EventID: 4624  # Successful logon
        LogonType: 3   # Network logon
        TargetUserName: 'admin'
    condition: selection
    timeframe: 5m
falsepositives:
    - Legitimate admin logins
level: medium

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2026-8651 MOVEit Transfer Authentication Bypass Attempt";
    flow:to_server,established;
    content:"Authorization"; http_header;
    content:"Bearer"; distance:0; within:100;
    pcre:"/Bearer\s+[A-Za-z0-9_-]{20,}/";
    sid:1000001;
    rev:1;
    reference:url,nvd.nist.gov/vuln/detail/CVE-2026-8651;
    metadata:created_at 2025_04_10, updated_at 2025_04_10;
)

Remediation & Mitigation

1. Immediate Patch: Upgrade to MOVEit Transfer 2025.0.7 or 2025.1.3 as per the vendor advisory.
2. Workaround: If patching is not immediately possible, restrict access to the HTTPS module using a web application firewall (WAF) with rules to block malformed authentication headers.
3. Network Controls: Place MOVEit Transfer behind a VPN or zero-trust proxy to limit exposure.
4. Monitoring: Enable detailed logging for all authentication attempts and review logs for suspicious activity.
5. Vendor Communication: Monitor Progress Software's security advisories for updates.

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