Mongobleed: Everything you need to know
What you’ll learn in this article:
- Mongobleed is a new vulnerability affecting MongoDB databases, named after its similarities to the Heartbleed vulnerability from 2014, which affected the OpenSSL cryptographic library
- The vulnerability can steal passwords, API keys, usernames, tokens, logs, and other sensitive data, triggered before the authentication stage
- Between 86,000 and 200,000 databases are estimated to still be affected, but there is already a patch that protects data admins from further exploitation
We recently covered React2Shell, a vulnerability that left over 640,000 domains still at risk — as of the writing of that article.
Now, a new exploit is putting MongoDB admins’ data at risk.
But before we take a look at Mongobleed, we should take a look at the exploit it’s named after. It’s not just the name — both exploits work almost identically.
💔 Heartbleed
What is it?
Heartbleed (designated as CVE-2014-0160) was a massive exploit in OpenSSL — effectively the default cryptographic library that most of the internet runs on.
Discovered back in 2014, the exploit made it easy to attack servers and steal sensitive information — including private keys, usernames, passwords, and other confidential data.
💔 Heartbleed
How did it work?
If two systems need to remain connected (a server and a browser, for example) after exchanging data, they keep sending each other additional packets of data (usually empty) at set intervals.
For example, one end of the connection could send 4KB of data, and the other end would send 4KB back — a completely reciprocal interaction.
This is called a “heartbeat.”
And the exploit worked like this:
2. Since a server has a limited amount of memory, it needs to make space for the new data it’s processing. That means that some of its own data needs to be sent back to the attacker.
3. The attacker only needs to send a small amount of data — as little as 1 bit — the server would immediately trust the data’s claimed size without checking. The attacker could claim they're sending 64KB — and get 64KB back — while only sending out a single bit.
4. The server wouldn’t care about what it’s sending back. It just needs to send something back. And that includes sending sensitive data.
5. On its own, this isn’t that big of a deal, despite still being a vulnerability.
6. But do this 10,000 times, and you can suddenly harvest immense amounts of data from a vulnerable server.
The best part?
No authentication required. No logs generated. Completely silent.
A practically fool-proof attack.
💔 Heartbleed
How did it affect users?
On the scale of 1 to 10, this is an 11."
— Bruce Schneier
What did it look like in the real world? Here’s just two examples.
- Around 900 users of the Canadian Revenue Agency had their insurance numbers stolen.
- And 4.5M patient records were stolen from Community Health Systems Inc.
Heartbeats that bleed data — Heartbleed.
💔 Heartbleed
Aftermath & solutions
Heartbleed made the industry stop in its tracks and reevaluate its approaches. It was a watershed moment for internet security.
But for the overall cybersecurity landscape? That’s where the true change happened.
It was truly one of the most transformative events in online security.
Heartbleed led to a complete reworking of how we see data and user safety online — a benefit we’re still pulling from today.
Unfortunately, a similar exploit has just been discovered. This time, in MongoDB.
🍃 Mongobleed
What is it?
So, even just the name “Mongobleed” should ring alarm bells in your mind after we’ve just discussed Heartbleed.
But how is it similar?
Discovered on December 12th, disclosed on December 19th, and designated as CVE-2025-14847 — it’s currently wreaking havoc across MongoDB servers.
And the similarities to Heartbleed are numerous.
This exploit is unauthenticated, memory-leaking, and high-impact.
It works almost identically, too.
🍃 Mongobleed
How does it work?
Here's exactly how it works.
2. This time, the data packet is compressed — using zlib.
3. When the compressed data is sent, the server receives two pieces of information:
a: A How large the compressed file is.
b: How large the uncompressed file inside it is.
4. The attacker lies about the size of what’s inside — it’s much, much smaller than the server thinks it is.
5. Therefore, the server returns tons more data than it received — back to the attacker.
6. As before, the information sent back by the server contains fragments of sensitive data.
7. When the attacker overwhelms the server with enough attacks, those tons of fragments can then easily be reconstructed.
Almost identical to Heartbleed. The only real change is the addition of zlib compression.
But that tiny detail?
It makes this exploit even more catastrophic.
🍃 Mongobleed
How is it affecting users?
Not great.
As of December 27th, over 87,000 MongoDB servers were estimated to be vulnerable.
According to security researcher Kevin Beaumont, there could be over 200,000 instances.
— Kevin Beaumont
And according to Wiz, 42% of cloud environments have at least one MongoDB instance running a vulnerable version.
The most high-profile confirmed incident so far was the attack on Ubisoft’s Rainbow Six Siege servers, breached over the 2025 holidays.
Despite Mongobleed’s high-risk profile, this is the only confirmed breach so far — though there will undoubtedly be more coming to light in the near future.
🍃 Mongobleed
What you can do
First, let’s look at the scope, as it’s significant.
MongoDB is one of the world's most popular databases, with widespread adoption across startups, enterprises, and cloud deployments.
● 3.6.0 through 4.4.29
● 5.0.0 through 5.0.31
● 6.0.0 through 6.0.26
● 7.0.0 through 7.0.27
● 8.0.0 through 8.0.16
● 8.2.0 through 8.2.2
Any MongoDB deployment with zlib compression enabled (which is common for performance optimization) is vulnerable. CISA added exactly this combination of factors to their Known Exploited Vulnerabilities catalog on December 29, 2025, confirming active exploitation in the wild.
The fix itself was simple, but the window between disclosure and patching gave malicious actors a significant head start.
1. Update to a patched MongoDB version immediately
End-of-life versions (4.2.x, 4.0.x, 3.6.x) have no patches available to them. Some services — like MongoDB Atlas — automatically provide these patches. If you’re running your own server, you’ll have to do this manually.
2. Disable zlib
If a patched version is available to you, disable zlib compression immediately — this is the workaround, as the exploit only works with zlib-enabled servers.
3. Check if your MongoDB database is exposed to the internet
The vulnerability primarily targets port 27017. If your port 27017 or any other ports are publicly accessible, you're at a much higher risk. Ideally, MongoDB should only be reachable from your application servers, not the open internet.
If you suspect compromise, it’s better to err on the side of caution and assume you have been breached. Here’s what you can do:
1. Look for signs of compromise.
Check server logs for unusual connection patterns, just in case. Keep in mind that Mongobleed doesn’t leave obvious traces, so if you don’t find anything suspicious, that doesn’t automatically mean you’re safe.
2. Rotate credentials
If you’re using a vulnerable version with zlib compression enabled — especially if internet-exposed — then it’s best to assume credentials may have leaked. Rotate passwords, keys, and tokens in order to minimize data theft.
🎓 What's the lesson here?
The real story here is how we approach open-source software security.
OpenSSL, MongoDB, zlib — all open-source.
A huge portion of industry-standard software, standards, and protocols are based on open-source software. That makes them prime targets for exploitation.
While yes, a big part of the open-source ethos is that the code is viewable by anyone — and therefore auditable by anyone — it also opens the door for experimentation and penetration at the hands of malicious actors.
In our React2Shell article, we provided these two figures, quoted from OWASP:
“91% of codebases contain components that have had no new development in over two years”
— Open Worldwide Application Security Project
They are just as relevant here.
Staying up-to-date with both your codebase and with recent developments can be challenging, especially when updating could break your entire operation.
Which is why it’s so essential to be forward-thinking when you build anything.
For databases specifically?
You can always count on us to have your back.
🚀 Check out our demo here.