An early end to the holidays: ‘Heartbleed of MongoDB’ is now under active exploit

December 30, 2025 TH Author

A high-severity MongoDB Server vulnerability, for which proofs of concept emerged over Christmas week, is now under active exploitation, according to the US Cybersecurity and Infrastructure Security Agency.

It wouldn’t be the holiday break without a potentially devastating security vulnerability popping up to crash the PTO party, and this one definitely fits the bill, with one expert calling it “basically Heartbleed for MongoDB.”

Yeah, it’s that serious.

Identified as CVE-2025-14847, this CVSS 8.7 vulnerability in the widely used open-source MongoDB Server stems from mismatched length fields in zlib-compressed protocol headers. If exploited with a malformed packet, an unauthenticated remote attacker can read uninitialized heap memory. As OX Security pointed out on Christmas Eve, that means an attacker could expose user info, passwords, API keys, and more.

“Although the attacker might need to send a large amount of requests to gather the full database, and some data might be meaningless, the more time an attacker has the more information could be gathered,” OX said. You know – time like they’d have over the Christmas holiday while the threat watchers are busy sucking down eggnog.

Dubbed MongoBleed by the Elastic Security researcher who published a proof of concept on December 26, the vulnerability was actually identified back on December 15 and patched by the MongoDB crew shortly thereafter. It affects a wide range of MongoDB Server versions, with MongoDB urging affected users to upgrade to fixed releases immediately.

“If you cannot upgrade immediately, disable zlib compression on the MongoDB Server,” the MongoDB maker urged.

Any internet-exposed MongoDB Server running a vulnerable version is open to attack, and OX noted that private servers reachable through lateral movement by attackers are also ripe for the plucking, should they be ferreted out.

The specifics of the vulnerability stem from the network transport layer of MongoDB, which OX noted can be forced to allocate or process undersized buffers during decompression of network messages. The zlib message compressor used by MongoDB, prior to the patch deployed to fix the issue, was coded to return the output length instead of just the actual length of decompressed data, meaning it could be tricked into spilling whatever was in the allocated memory instead of just the real length of the decompressed data. Oops.

“This type of vulnerability is a frequent attack vector for malicious cyber actors and poses significant risks to the federal enterprise,” CISA noted in its Monday addition of MongoBleed to its known exploited vulnerabilities catalog.

Welcome back from the holiday break, whether you returned as scheduled or to deal with this actively exploited vulnerability, which appeared on the web just as Santa was prepping to deliver gifts. Hopefully he uses a different database provider, or has his systems patched already. ®