Introduction
A critical pre-authentication memory leak is a severe security vulnerability that allows attackers to extract sensitive memory data before any user authentication takes place.
MongoBleed (CVE-2025-14847) is a critical security vulnerability affecting MongoDB Server that allows a remote, unauthenticated attacker to extract sensitive data directly from a database server’s memory. Unlike traditional database vulnerabilities that rely on authentication bypass or misconfiguration, MongoBleed occurs before authentication, making it especially dangerous for any MongoDB instance reachable over a network.
The vulnerability has gained significant attention because public proof-of-concept exploits are already available, and exploitation requires no special privileges or credentials. In practice, an attacker only needs network access to the MongoDB service to begin leaking memory contents.
Understanding the Root Cause
MongoDB supports network message compression to reduce bandwidth usage and improve performance. One of the supported compression algorithms is zlib, which compresses messages before they are transmitted between client and server.
When MongoDB receives a compressed message, it relies on a size value provided in the message header to determine how much memory should be allocated for decompression. The flaw exists because MongoDB trusts this size value without sufficient validation.
An attacker can deliberately craft a compressed message that claims to decompress into a much larger buffer than the actual payload provides. MongoDB allocates memory based on this incorrect size, but only part of the allocated memory is initialized with real data. The remaining portion contains uninitialized heap memory—data left over from previous operations.
Under certain error conditions or response paths, MongoDB returns this memory back to the client, unintentionally leaking internal server memory.
This behavior is conceptually similar to the infamous Heartbleed vulnerability, where uninitialized memory was returned due to improper bounds checking.
What Data Can Be Exposed
Because the vulnerability leaks raw heap memory, the exposed data is unpredictable but potentially severe. Depending on server activity and memory reuse, leaked data may include:
- Database usernames and passwords
- Application secrets and API keys
- Authentication tokens and session identifiers
- Configuration values
- Recently processed query data
- Personally identifiable information (PII)
Even environments that rely on encryption at rest or strict database permissions are not immune, as secrets often exist in plaintext in memory during normal operation.
Exploitation in the Real World
MongoBleed is particularly concerning because exploitation does not require authentication and happens at the network protocol level. The release of public exploit code has significantly lowered the barrier for attackers, making automated scanning and exploitation feasible at scale.
Attackers can repeatedly send crafted compressed packets to a vulnerable MongoDB instance and gradually extract chunks of memory. Over time, this can yield enough sensitive information to pivot deeper into the environment or compromise connected applications.
The vulnerability impacts a wide range of MongoDB releases across multiple major versions. Supported branches received patches, but older end-of-life versions remain vulnerable. permanently vulnerable. Any MongoDB instance with zlib compression enabled and exposed to untrusted networks should be considered at risk.
Affected Versions
The vulnerability impacts a wide range of MongoDB releases across multiple major versions. Supported branches received patches, but older end-of-life versions remain permanently vulnerable. Any MongoDB instance with zlib compression enabled and exposed to untrusted networks should be considered at risk.
| Affected Version | Fixed Version |
|---|---|
| MongoDB Server v3.6 (All Versions) | Upgrade to MongoDB 8.2.3, 8.0.17, 7.0.28, 6.0.27, 5.0.32, 4.4.30 or later |
| MongoDB Server v4.0 (All Versions) | Upgrade to MongoDB 8.2.3, 8.0.17, 7.0.28, 6.0.27, 5.0.32, 4.4.30 or later |
| MongoDB Server v4.2 (All Versions) | Upgrade to MongoDB 8.2.3, 8.0.17, 7.0.28, 6.0.27, 5.0.32, 4.4.30 or later |
| MongoDB 4.4.0 through 4.4.29 | Upgrade to MongoDB 4.4.30 or later |
| MongoDB 5.0.0 through 5.0.31 | Upgrade to MongoDB 5.0.32 or later |
| MongoDB 6.0.0 through 6.0.26 | Upgrade to MongoDB 6.0.27 or later |
| MongoDB 7.0.0 through 7.0.26 | Upgrade to MongoDB 7.0.28 or later |
| MongoDB 8.0.0 through 8.0.16 | Upgrade to MongoDB 8.0.17 or later |
| MongoDB 8.2.0 through 8.2.2 | Upgrade to MongoDB 8.2.3 or later |
