MongoBleed (CVE-2025-14847) Information Leak Vulnerability Exploited in the Wild

Overview

A critical high-severity vulnerability, tracked as CVE-2025-14847 and nicknamed MongoBleed, has been disclosed in MongoDB Server and is already being actively exploited in the wild. This flaw enables unauthenticated remote attackers to “bleed” uninitialized heap memory from the database server, potentially exposing sensitive information, including database credentials, API keys, session tokens, and Personally Identifiable Information (PII).

MongoBleed is particularly dangerous because it can be exploited over the network without valid credentials or user interaction. The vulnerability is now confirmed to be actively exploited in the wild, and the U.S. Cybersecurity and Infrastructure Security Agency (CISA) has added it to its Known Exploited Vulnerabilities (KEV) Catalog. Approximately 87,000 to 200,000 MongoDB instances are estimated to be exposed to the internet, making this a widespread threat.

The Threat

The successful exploitation of CVE-2025-14847 allows remote, unauthenticated attackers to “bleed” uninitialized heap memory from the MongoDB server process. This flaw can lead to the exposure of highly sensitive secrets, including plaintext database credentials, cloud API keys (such as AWS access keys), session tokens, and customer Personally Identifiable Information (PII). Given that MongoDB often houses core business data for critical sectors like fintech and healthcare, a compromise can result in massive data exfiltration, regulatory penalties, and a complete loss of confidentiality.

• Affected Product: MongoDB Server
• Vulnerability Type: Uninitialized Memory Read (Improper Handling of Length Parameter Inconsistency – CWE-130)
• CVSS Score: 8.7 (High)
• Active Exploitation: The vulnerability is currently being exploited in the wild and was added to CISA’s Known Exploited Vulnerabilities (KEV) Catalog on December 29, 2025.
• Attack Surface: Beyond the 87,000+ internet-exposed instances, many cloud environments contain at least one vulnerable internal MongoDB resource. These internal servers are at high risk if an attacker breaches the network and moves laterally.
• Affected Versions:
  • MongoDB 8.2 before 8.2.3
  • MongoDB 8.0 before 8.0.17
  • MongoDB 7.0 before 7.0.28
  • MongoDB 6.0 before 6.0.27
  • MongoDB 5.0 before 5.0.32
  • MongoDB 4.4 before 4.4.30
  • Legacy Versions: All 3.6, 4.0, and 4.2 versions are permanently vulnerable as they are End-of-Life (EOL) and will not receive patches.

Technical Breakdown

The root cause of MongoBleed lies in the zlib network message decompression logic within MongoDB’s network transport layer, specifically in ‘message_compressor_zlib.cpp’.:

1. Improper Length Handling: When a client sends a compressed network message, the server allocates a memory buffer to hold the decompressed data.
2. The Over-Read: In vulnerable versions, the server incorrectly returns the size of the allocated buffer ‘(output.length())’ instead of the actual length of the decompressed data.
3. Memory Disclosure: By sending a specially crafted, undersized compressed packet, an attacker causes the server to respond with a buffer that includes the small decompressed payload followed by adjacent, uninitialized heap memory.

This “over-read” is functionally similar to the infamous Heartbleed bug, allowing attackers to scrape fragments of the server’s memory repeatedly to reconstruct sensitive data.

Immediate Recommendations

Due to the active exploitation and ease of use of public Proof-of-Concept (PoC) exploits, immediate action is mandatory:

1. Patch Immediately: Upgrade self-managed MongoDB instances to the authoritative fixed versions (8.2.3, 8.0.17, 7.0.28, 6.0.27, 5.0.32, or 4.4.30).
2. Disable zlib Compression (Workaround): If patching is delayed, disable zlib compression by starting mongod or mongos with the –networkMessageCompressors option explicitly omitting zlib.
3. Restrict Network Exposure: Block inbound access to MongoDB (default port 27017) at the network perimeter; databases should only be reachable via VPNs or trusted management segments.
4. Rotate Secrets: Because credentials and session tokens may have been resident in memory, assume they are compromised and rotate all database passwords and API keys after patching.

How XM Cyber Can Help with CVE-2025-14847

The rapid exploitation of MongoBleed is driving security teams into a frantic race to patch every instance, reminiscent of past crises like Heartbleed. XM Cyber helps organizations move beyond this reactive “patch everything” treadmill by identifying which specific vulnerabilities actually jeopardize your critical assets.

XM Cyber External Attack Surface Management (EASM)
XM EASM identifies external-facing MongoDB instances vulnerable to this risk through continuous monitoring and automated scanning. The platform highlights which external instances provide the most direct paths to your internal network and critical systems, ensuring your most exposed entry points are addressed first.

XM Cyber Vulnerability Risk Management (VRM)
While internet-facing servers are high-priority targets, the massive volume of internal MongoDB instances creates a significant surface for lateral movement. CVE-2025-14847 is fully supported in the XM Cyber Vulnerability Risk Management (VRM), so you can identify all instances of the CVE-2025-14847 vulnerability across your organization.

Ready to shift from reactive patching to strategic risk reduction? Contact us to learn how.