MongoBleed: MongoDB Zlib Vulnerability (CVE-2025-14847) and how to remediate it

A high-severity vulnerability known as MongoBleed (CVE-2025-14847), was recently identified and patched in MongoDB, the widely used open-source NoSQL database. The issue, named for its ability to “bleed” uninitialized memory from the server, stems from improper handling of zlib-compressed wire protocol messages and allows unauthenticated remote attackers to leak sensitive process memory from vulnerable MongoDB instances.

The root cause of this vulnerability lies in MongoDB’s handling of zlib-compressed messages. Due to improper validation during decompression, the server may return uninitialized heap memory to the client. An attacker can exploit this behavior remotely and without authentication to leak sensitive data from the MongoDB process.

A proof-of-concept (PoC) exploit for MongoBleed was quickly released by Joe DeSimone, highlighting the ease with which this vulnerability can be exploited.

The mongobleed.py proof-of-concept demonstrates MongoBleed by abusing MongoDB’s handling of zlib-compressed wire protocol messages. The script sends a crafted OP_COMPRESSED message that advertises a large uncompressed size while containing only a minimal compressed payload.

In vulnerable MongoDB versions, the server allocates a buffer based on this claimed size but only partially fills it during decompression. Due to improper validation, MongoDB later treats the entire buffer as valid, causing uninitialized heap memory to be included in the response.

The PoC repeatedly sends these malformed messages while varying size parameters to leak different regions of heap memory over multiple requests. This occurs prior to authentication and requires only network access to the MongoDB port, demonstrating a reliable unauthenticated memory disclosure primitive rather than a crash or code-execution flaw.

The potential impact of this vulnerability is significant. Successful exploitation could allow an attacker to:

• Sensitive Memory Disclosure: Leak uninitialized heap memory from the MongoDB server process, potentially exposing credentials, authentication material, configuration data, or other in-memory secrets.
• Secondary Compromise Risk: Use leaked secrets as a stepping stone for further attacks, such as unauthorized database access or lateral movement within the environment.

The exploitation of this vulnerability aligns with the following tactics and techniques:

• TA0006 – Credential Access: Successful exploitation may expose authentication material or secrets residing in MongoDB’s process memory.
• TA0009 – Collection: Attackers can collect sensitive information by repeatedly triggering memory disclosure and aggregating leaked heap contents.
• T1005 – Data from Local System: Uninitialized memory returned by the server may contain locally stored or in-process data relevant to the MongoDB instance.

This flaw impacts the following MongoDB versions:

• MongoDB 8.2.0 through 8.2.2
• MongoDB 8.0.0 through 8.0.16
• MongoDB 7.0.0 through 7.0.27
• MongoDB 6.0.0 through 6.0.26
• MongoDB 5.0.0 through 5.0.31
• MongoDB 4.4.0 through 4.4.29
• All MongoDB Server v4.2 versions
• All MongoDB Server v4.0 versions
• All MongoDB Server v3.6 versions

To mitigate the risk associated with CVE-2025-14847, the following actions are strongly recommended:

• Upgrade Immediately: Upgrade to one of the fixed versions: 8.2.3, 8.0.17, 7.0.28, 6.0.27, 5.0.32, and 4.4.30.
• Disable zlib Compression: If an immediate upgrade is not possible, disable zlib compression on the MongoDB server. This can be done by starting mongod or mongos with a networkMessageCompressors or a net.compression.compressors option that explicitly omits zlib. Example safe values include snappy, zstd, or disabled.

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