MongoBleed (CVE-2025-14847) → The Spring Boot Fix

I thought we left memory leaks back in 2014 with Heartbleed. Turns out, I was wrong.

If you’re running MongoDB 5.0 through 8.0, your database is likely leaking uninitialized heap memory right now. No authentication needed. Attackers just hit port 27017 and your server hands over credentials, session tokens, and whatever else is sitting in RAM.

At www.codegigs.app, I’ve spent the last 48 hours patching this for our enterprise clients. The fix is simple, but if you mess up the config, you’ll kill your app’s performance.

Here is exactly how to stop the bleeding in your Spring Boot environment.

The 5-Minute Fix (Upgrade First)

Before we touch Java code, check your infrastructure. The vulnerability is in the MongoDB server’s zlib compression.

You need to be on these versions or higher:

• 8.2 → 8.2.3
• 8.0 → 8.0.17
• 7.0 → 7.0.28
• 6.0 → 6.0.27

If you use Docker Compose (which you should), update your tag immediately:

# docker-compose.yml
services:
  mongodb:
    # WAS: image: mongo:7.0.12
    # FIX: Explicitly pin the patched version
    image: mongo:7.0.28
    ports:
      - "27017:27017"
    environment:
      - MONGO_INITDB_ROOT_USERNAME=admin
      - MONGO_INITDB_ROOT_PASSWORD=secret

Restart the container. If you can’t upgrade yet (legacy systems are fun, aren’t they?), keep reading for the config workaround.

Am I Actually Vulnerable?

Maybe. But probably.

The CVE (CVE-2025-14847) attacks the zlib compression logic. When your Spring Boot app talks to Mongo, the driver usually negotiates compression to save bandwidth.

If your server has zlib enabled (it does by default) and is exposed to the network, an attacker sends a malformed packet. The server gets confused about buffer lengths and replies with raw memory.

Symptoms to look for:

• Connection spikes (50k+ per minute)
• Logs showing connections without metadata (Event ID 51800 missing)
• Random performance drops

Workaround: Disabling Zlib in Spring Boot (2026 Edition)

If you can’t patch the server immediately, you need to stop using zlib. While the server-side config is the primary fix, you should also align your Spring Boot client to stop requesting it.

In 2026, we’re mostly using Spring Boot 3.4+. Here is the modern configuration.

// MongoConfig.java
// Spring Boot 3.4.1, Spring Data Mongo 5.2
package app.codegigs.config;

import com.mongodb.ConnectionString;
import com.mongodb.MongoClientSettings;
import org.springframework.context.annotation.Configuration;
import org.springframework.data.mongodb.config.AbstractMongoClientConfiguration;

import java.util.Collections;

@Configuration
public class MongoConfig extends AbstractMongoClientConfiguration {

    @Override
    protected String getDatabaseName() {
        return "codegigs_db";
    }

    @Override
    public MongoClientSettings mongoClientSettings() {
        // Force the client to NEVER ask for zlib
        // We switch to Snappy (faster anyway) or disable it
        return MongoClientSettings.builder()
                .applyConnectionString(new ConnectionString("mongodb://admin:secret@localhost:27017/codegigs_db"))
                .compressorList(Collections.emptyList()) // Option A: Disable all compression
                // .compressorList(List.of(MongoCompressor.createSnappyCompressor())) // Option B: Use Snappy
                .build();
    }
}

Why this works

Line 26 is the nuclear option. By passing an empty list to compressorList, your Spring Boot application tells the server “I don’t support compression.”

However, this only protects your app’s connection. It does not patch the server. An attacker can still connect with a Python script and trigger the bleed. You MUST configure the server mongod.conf too:

# mongod.conf
net:
   compression:
      compressors: snappy,zstd  # REMOVE zlib from this list

I missed this step on a staging cluster last week. We patched the Java app but left the server config open. The security scan flagged it 10 minutes later. Felt like an idiot.

Checking Your Dependencies

This vulnerability is weird because it’s a server-side C++ issue, but your Java drivers matter for compatibility. In late 2025, you should be on the 5.x driver series.

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-mongodb</artifactId>
    <version>3.4.1</version>
</dependency>

Check your effective pom. If you see mongodb-driver-sync version 4.x, you’re running old code. It works, but you’re missing out on the automatic zstd support that replaces the vulnerable zlib.

Common Mistakes (Don’t Do This)

1. Firewalling isn’t enough

I hear this constantly: “My database is in a private subnet, so I’m safe.”

No, you’re not. If an attacker gets into a web container (via Log4j 3.0 or whatever new nightmare we have this week), they can pivot to the database. If that DB is vulnerable to MongoBleed, they can dump credentials without a password. Internal threats are still threats.

2. Ignoring the logs

The exploit is noisy. It generates thousands of connections. Set up a Logback filter to catch this.

<configuration>
    <logger name="org.mongodb.driver.connection" level="INFO" />
</configuration>

If you see a flood of “Opened connection” followed instantly by “Closed connection” with no queries in between, someone is probing your zlib handler.

What’s Next?

Patching CVE-2025-14847 is mandatory. Do not wait for the weekend window.

1. Update your Docker images to the patched versions (8.0.17+).
2. Rotate your database credentials. If you were exposed, assume your admin password is gone.
3. Disable zlib in mongod.conf if you can’t patch today.

This stuff happens. The key isn’t writing perfect code, it’s reacting fast when the platform breaks.

For a complete guide on building resilient Spring Boot systems that survive these CVEs, check out the advanced tracks at www.codegigs.app.