In late 2025, a critical vulnerability in the widely used NoSQL database MongoDB - now nicknamed MongoBleed because it works exactly like Heartbleed did eleven years ago, and tracked as CVE-2025-14847 - emerged as both a serious security threat and a likely root cause of a major real-world breach. On December 27, 2025, Ubisoft’s Rainbow Six Siege suffered a severe server compromise that forced the company to take the game offline after attackers manipulated internal systems, distributed billions of in-game credits, and tampered with moderation tools. Researchers and incident reports now link this breach to exploitation of the MongoBleed flaw shortly after a proof-of-concept exploit became public. (Tom's Guide)
What MongoBleed Is
MongoBleed is an unauthenticated memory disclosure vulnerability in MongoDB’s zlib compression handler for network messages. When a MongoDB server processes malformed compressed data, it can return uninitialized heap memory to the attacker. This memory may contain sensitive information such as credentials, session tokens, API keys, and internal server state - all without requiring any login or authentication. Because the issue occurs before authentication is checked, even well-secured databases are vulnerable if they are reachable on the network. (wiz.io)
Why It’s Dangerous
A combination of factors makes MongoBleed especially severe:
- Unauthenticated remote exploitation: Attackers need no valid credentials, only network access to a vulnerable MongoDB instance. (Bitsight)
- Broad version exposure: Most MongoDB releases from 2017 through late-2025 were affected if zlib compression was enabled — a common default. (BAYSEC - Insights)
- Active exploitation: A working exploit tool circulated quickly after disclosure, and researchers observed attackers using it against internet-exposed instances. (CyberDesserts)
- Real-world impact: Multiple threat actors reportedly turned this vulnerability into a major intrusion vector targeting Ubisoft, with claims that they used MongoBleed to reach backend systems and potentially even internal repositories. (Tom's Guide)
Connection to the Rainbow Six Siege Breach
The timing of the Rainbow Six Siege incident aligns closely with public disclosures and proof-of-concept code for MongoBleed. On December 27, hackers accessed Ubisoft’s infrastructure, manipulated Rainbow Six Siege accounts — granting massive amounts of in-game currency and issuing fake moderation actions — and caused Ubisoft to take servers offline for remediation. Security reports now describe this breach in terms that match known MongoBleed exploitation behavior, and some cybersecurity sources explicitly point to CVE-2025-14847 as the likely exploited vector. (Tom's Guide)
References
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Tom’s Guide: Massive Rainbow Six Siege breach reportedly linked to MongoBleed flaw
https://www.tomsguide.com/computing/online-security/massive-rainbow-six-siege-breach-reportedly-linked-to-mongobleed-flaw-everything-you-need-to-know (Tom's Guide) -
Security Boulevard: Threat Actors Exploiting Critical ‘MongoBleed’ MongoDB Flaw
https://securityboulevard.com/2025/12/threat-actors-exploiting-critical-mongobleed-mongodb-flaw/ (Security Boulevard) -
Baysec Insights: MongoBleed vulnerability analysis and Rainbow Six Siege incident
https://insights.baysec.eu/mongobleed-cve-2025-14847-vulnerability-analysis-and-the-rainbow-six-siege-incident (BAYSEC - Insights) -
Wiz Blog: MongoBleed (CVE-2025-14847) exploited in the wild
https://www.wiz.io/blog/mongobleed-cve-2025-14847-exploited-in-the-wild-mongodb (wiz.io) -
MongoDB Security Advisory Reporting: MongoDB warns admins to patch severe vulnerability immediately
https://www.bleepingcomputer.com/news/security/mongodb-warns-admins-to-patch-severe-vulnerability-immediately/ (BleepingComputer) -
MongoBleed Detector Tool (CyberPress): Tool to identify MongoBleed vulnerability
https://cyberpress.org/mongobleed-detector-tool-released-to-identify-mongodb-vulnerability-cve-2025-14847/ (Cyber Security News)