CVE-2026-4147: Information Disclosure Vulnerability

CVE-2026-4147 Overview

An authenticated user with the read role may read limited amounts of uninitialized stack memory via specially-crafted issuances of the filemd5 command. This uninitialized memory use vulnerability (CWE-457) allows attackers with minimal authentication to potentially access sensitive data that remains in stack memory from previous operations.

Critical Impact

Authenticated attackers can leverage the filemd5 command to read uninitialized stack memory, potentially exposing sensitive information from prior database operations.

Affected Products

• MongoDB Server (specific versions to be confirmed via vendor advisory)

Discovery Timeline

• 2026-03-17 - CVE CVE-2026-4147 published to NVD
• 2026-03-18 - Last updated in NVD database

Technical Details for CVE-2026-4147

Vulnerability Analysis

This vulnerability stems from improper memory initialization within the MongoDB server when handling the filemd5 command. The filemd5 command is typically used to compute the MD5 hash of files stored in GridFS, MongoDB's specification for storing large files. When crafted requests are sent to this command endpoint, the server fails to properly initialize stack memory before use, allowing portions of uninitialized memory to be returned to the authenticated user.

The attack requires network access and authentication with at least a read role, lowering the barrier for exploitation in multi-tenant environments or where read access is broadly granted. While confidentiality is highly impacted, integrity and availability remain unaffected according to the vulnerability assessment.

Root Cause

The root cause is classified under CWE-457 (Use of Uninitialized Variable). The filemd5 command handler allocates stack memory for processing but fails to properly initialize this memory before use. When certain edge cases or malformed requests are processed, the uninitialized memory contents may be inadvertently included in the response sent back to the client.

This type of vulnerability typically occurs when:

• Stack buffers are allocated but not zero-initialized
• Error handling paths skip initialization steps
• Optimizations remove initialization code that appeared unnecessary

Attack Vector

The attack is network-based and requires an authenticated session with read privileges. An attacker would craft specially-formatted filemd5 command requests designed to trigger code paths where uninitialized stack memory is read and returned. The limited nature of the leak means multiple requests may be needed to extract meaningful data.

The exploitation process involves:

1. Establishing an authenticated connection to the MongoDB instance
2. Sending specially-crafted filemd5 commands with parameters designed to trigger the vulnerable code path
3. Analyzing responses for leaked stack memory contents
4. Repeating the process to accumulate sensitive information fragments

For technical details on this vulnerability, refer to the MongoDB Jira Bug Report.

Detection Methods for CVE-2026-4147

Indicators of Compromise

• Unusual patterns of filemd5 command executions, particularly with malformed or edge-case parameters
• Repeated filemd5 requests from the same authenticated session in rapid succession
• Error logs indicating unexpected behavior in GridFS-related command processing
• Audit log entries showing filemd5 commands against non-existent or invalid GridFS collections

Detection Strategies

• Enable MongoDB profiling to capture all filemd5 command executions and review for anomalous patterns
• Configure audit logging to track command execution with detailed parameter logging
• Implement rate limiting or alerting on excessive filemd5 command usage from individual users
• Deploy network monitoring to detect unusual data patterns in MongoDB wire protocol responses

Monitoring Recommendations

• Review MongoDB slow query logs for unusual filemd5 command patterns
• Monitor for increases in memory-related errors in MongoDB server logs
• Set up alerts for multiple failed or unusual filemd5 operations within short time windows
• Audit read role assignments to ensure principle of least privilege is followed

How to Mitigate CVE-2026-4147

Immediate Actions Required

• Review the MongoDB Jira Bug Report for the latest patch information
• Audit all accounts with read role access and remove unnecessary permissions
• Monitor filemd5 command usage across your MongoDB deployments
• Consider temporarily restricting filemd5 command access if not business-critical

Patch Information

Consult the official MongoDB security advisory and the MongoDB Jira Bug Report for specific patch versions that address this vulnerability. Ensure you update to the patched version as soon as it becomes available for your deployment.

Workarounds

• Implement network segmentation to limit who can access MongoDB instances directly
• Review and restrict read role grants to only essential users and applications
• Enable MongoDB authentication if not already enabled and audit existing credentials
• Consider using a firewall or proxy to filter potentially malicious filemd5 commands until patched

# Review current users with read permissions
mongosh --eval "db.getUsers().forEach(function(user) { printjson(user.roles); })"

# Enable profiling to capture filemd5 commands (level 2 = all operations)
mongosh --eval "db.setProfilingLevel(2, { filter: { 'command.filemd5': { \$exists: true } } })"