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Critical MongoDB Advisory: Fix CVE-2025-14847 (MongoBleed) Before It Bites

Publication date: 2025-12-29
WARNING

We hope you all had a wonderful Christmas and are looking forward to the new year. Unfortunately, as the final days of 2025 demonstrate once again, cybersecurity never sleeps. While many organizations were operating with reduced staff over the holidays, attackers were quick to capitalize on a newly disclosed and highly impactful vulnerability in MongoDB.

Over the past days, multiple national cyber authorities have issued warnings about active exploitation of CVE-2025-14847, better known as MongoBleed. The Dutch National Cyber Security Centre (NCSC) warned that exploitation was expected shortly after proof-of-concept code appeared online, and the Australian Cyber Security Centre (ACSC) has since confirmed it is aware of active global exploitation and urges organizations to patch immediately and investigate for potential compromise.

What is MongoBleed?

CVE-2025-14847 is a high-severity information disclosure vulnerability (CVSS 8.7) in MongoDB Server. It allows a remote, unauthenticated attacker to read uninitialized heap memory from a MongoDB process. The root cause lies in improper handling of length parameters in zlib-compressed MongoDB protocol headers. By sending malformed compressed network packets, an attacker can trigger MongoDB to return memory buffers that may include credentials, session tokens, API keys, internal pointers, or other sensitive in-memory data.

For a detailed, annotated breakdown from our side — including an EPSS graph, an attack flow graph, a Q&A, and an AI assistant — see our BaseFortify CVE report: https://basefortify.eu/cve_reports/2025/12/cve-2025-14847.html.

What makes this vulnerability especially dangerous

MongoBleed is particularly serious because exploitation happens pre-authentication and does not require user interaction. Even if each response leaks only a small fragment of memory, repeated requests can allow an attacker to collect increasingly valuable data over time. The Dutch NCSC notes that an exploit has been published and it expects active exploitation in the short term, while the ACSC states it is aware of active global exploitation and recommends urgent action.

Affected versions

This vulnerability affects a broad range of MongoDB releases. According to NVD and MongoDB’s own guidance, impacted versions include MongoDB Server v8.2 prior to 8.2.3, v8.0 prior to 8.0.17, v7.0 prior to 7.0.28, v6.0 prior to 6.0.27, v5.0 prior to 5.0.32, v4.4 prior to 4.4.30, and MongoDB Server versions 4.2, 4.0, and 3.6 (within the affected ranges described by the advisory sources).

How to check if you are vulnerable

Step 1: Check your MongoDB version.

mongod --version

If you only have client access, you can try:

mongo --eval 'db.version()'

If the version matches an affected range and you have not upgraded to a fixed release (listed below), you should treat the instance as vulnerable.

Step 2: Check whether zlib compression is enabled. (It is commonly enabled by default in many deployments.)

mongo --eval 'db.adminCommand({ getParameter: 1, networkMessageCompressors: 1 })'

If you see zlib in the returned compressors list, the vulnerable code path is relevant.

Step 3: Confirm whether your server is exposed. From a location outside your network (or via a controlled external scanner), check whether TCP/27017 is reachable. If you manage the host directly, you can at least verify what it is listening on:

sudo ss -lntp | grep 27017

If you see MongoDB listening on 0.0.0.0:27017 or a public interface address, review firewall rules and cloud security groups immediately.

Remediation and mitigation

Upgrade immediately. MongoDB has released patched versions that fully address CVE-2025-14847. Upgrade to one of the following fixed versions: 8.2.3, 8.0.17, 7.0.28, 6.0.27, 5.0.32, or 4.4.30.

If upgrading is not immediately possible, MongoDB and the NCSC recommend temporarily disabling zlib compression and using an alternative compressor such as snappy or zstd, or disabling compression entirely. (Exact configuration varies by environment; see the MongoDB references below for the official options via networkMessageCompressors / net.compression.compressors.)

In parallel, reduce network exposure where possible (private networking, allowlists, VPN access) and monitor for unusual pre-authentication connection patterns. Given confirmed active exploitation, it is also prudent to investigate for potential compromise, especially on internet-reachable instances.

What this means for organizations

MongoBleed is a reminder that low-level implementation details (like compression and message parsing) can have high-impact consequences. Even well-managed environments can be caught off-guard when defaults introduce unexpected attack paths. The most practical takeaway is to combine fast patching with exposure review: know where MongoDB exists, which versions are running, and which instances are reachable from where.

How BaseFortify can help

With BaseFortify, organizations don’t need to chase every alert manually. You simply enter the software components you rely on (for example: MongoDB and the version you are running), and BaseFortify continuously matches those components against newly published and updated CVEs. When a match is found—such as CVE-2025-14847 affecting MongoDB—it automatically triggers a clear mitigation track: you see the severity and exploit signals, get practical remediation guidance (patch versions, configuration mitigations like disabling zlib), and can track the status of your response. If you want to unlock these features, register here: https://basefortify.eu/register.

Sources and further reading

As we move into the new year, CVE-2025-14847 is a timely reminder that attackers do not pause for holidays. If you rely on MongoDB, now is the time to verify versions, reduce exposure, patch urgently, and investigate where appropriate.