CVE-2025-14847: MongoDB zlib Compression Memory Disclosure

Executive Summary

A critical unauthenticated vulnerability (CVE-2025-14847) has been identified in MongoDB Server, affecting how the database processes zlib-compressed network traffic.

Under specific conditions, a remote attacker can trigger MongoDB to return uninitialized heap memory as part of a server response. Because this data originates from process memory, it may contain fragments of previously handled data, internal state, or sensitive values.

No authentication is required. The only prerequisite is network access to a MongoDB instance with compression enabled.

This issue turns internal memory into attacker-observable output.

What Is MongoDB?

MongoDB is a widely used NoSQL document database, commonly deployed as a core backend component in modern applications. It is frequently used for:

• Application data storage
• User profiles and session data
• Internal service state
• Analytics and logging pipelines

MongoDB supports network-level compression to reduce bandwidth usage between clients and servers. One of the supported compression algorithms is zlib, which is where this vulnerability originates.

Because MongoDB is often exposed inside cloud environments – sometimes unintentionally – flaws in its network protocol handling have a large blast radius.

What Versions Are Affected?

CVE-2025-14847 affects multiple MongoDB major releases:

Vulnerable versions include:

• MongoDB 3.6.x
• MongoDB 4.0.x
• MongoDB 4.2.x
• MongoDB 4.4.x ≤ 4.4.29
• MongoDB 5.0.x ≤ 5.0.31
• MongoDB 6.0.x ≤ 6.0.26
• MongoDB 7.0.x ≤ 7.0.26
• MongoDB 8.0.x ≤ 8.0.16
• MongoDB 8.2.x ≤ 8.2.2
  

Fixed versions:

• 4.4.30
• 5.0.32
• 6.0.27
• 7.0.28
• 8.0.17
• 8.2.3

Root Cause: What Goes Wrong

The vulnerability exists in MongoDB’s handling of compressed protocol messages.

At a high level:

• MongoDB accepts zlib-compressed requests at the network layer
• Certain malformed compressed frames cause a length mismatch during decompression
• As a result, MongoDB may include uninitialized heap memory in its response

The leaked memory originates from the MongoDB process itself and was never intended to be returned to clients.

Impact: What Data Can Leak?

Depending on heap layout and request timing, leaked memory may contain:This memory was never meant to be returned to the client. Depending on timing and heap layout, leaked data may include:

• Parts of previous query results
• Internal server state
• Recently handled sensitive values
• Residual authentication-related data

No authentication is required. Network access alone is sufficient.

How to Identify If You Are Vulnerable

1. Check Your MongoDB Version

If you are running any MongoDB version listed above and have not upgraded to a fixed release, you should assume exposure.

2. Check Whether Compression Is Enabled

MongoDB enables network compression through client and server negotiation. If your deployment supports or allows zlib compression, the vulnerable code path may be reachable.

3. Check Network Exposure

Risk increases significantly if MongoDB is:

• Accessible from untrusted networks
• Exposed to VPC peers or shared cloud environments
• Reachable by CI/CD systems, agents, or third-party services

Any network path into MongoDB expands the attack surface for unauthenticated exploitation.

How to Prevent It

1. Upgrade MongoDB

The most effective mitigation is upgrading to a fixed MongoDB release listed above. This ensures proper validation and safe handling of compressed network data.

2. Restrict Network Access

MongoDB should never be broadly reachable. Apply:

• Firewall rules
• Security group restrictions
• Private network isolation

Only trusted application components should be able to connect.

3. Disable zlib Compression (If Possible)

If upgrades are delayed, disabling zlib compression can reduce exposure until patches are applied.

4. Monitor for Anomalous Protocol Behavior

Unexpected compressed requests, malformed frames, or abnormal response sizes should be treated as suspicious signals.

Securing MongoDB Deployments with Upwind

Patching is critical, but visibility matters just as much. Upwind helps teams manage risks like CVE-2025-14847 by identifying vulnerable MongoDB versions across cloud environments, detecting exposed database services and unintended network paths, monitoring runtime behavior for anomalous protocol activity, and highlighting risky configurations that unnecessarily expand blast radius.