Executive Summary

On December 19, 2025, MongoDB disclosed CVE-2025-14847, a high-severity (CVSS 8.7) information disclosure vulnerability nicknamed "MongoBleed." This flaw affects MongoDB database servers that use zlib for network message compression. A remote, unauthenticated attacker can exploit this vulnerability by sending a specially crafted message to the server. This triggers a memory leak, causing the server to return uninitialized heap memory, which may contain sensitive data from other concurrent sessions. This leaked data can include plaintext passwords, API keys, session tokens, and other critical secrets. The vulnerability is being actively exploited in the wild, and a proof-of-concept (PoC) is publicly available, dramatically increasing the risk. MongoDB has released patched versions and advises customers to upgrade immediately or implement workarounds. Due to the nature of the data leak, rotating all credentials after patching is a critical remediation step.

Vulnerability Details

CVE-2025-14847, or "MongoBleed," is an unauthenticated memory leak vulnerability rooted in the way MongoDB's server handles zlib-compressed client messages.

• Vulnerability Type: Uninitialized Data Exposure
• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: None
• User Interaction: None

The exploit works when an attacker sends a message to the server that is flagged for zlib decompression. The message is malformed in a way that it declares a very large uncompressed size, but the actual compressed payload is small. The server allocates a large buffer in memory based on the declared size but only fills a small portion of it with the decompressed data. When sending the response, the server incorrectly sends back the entire buffer, including the large, uninitialized portion. This uninitialized memory can contain fragments of data from other processes and sessions being handled by the server, effectively 'bleeding' sensitive information.

Affected Systems

The vulnerability affects a wide range of MongoDB server versions where zlib is enabled for network compression:

• MongoDB 8.0: Versions 8.0.0 - 8.0.4
• MongoDB 7.0: Versions 7.0.0 - 7.0.10
• MongoDB 6.0: Versions 6.0.0 - 6.0.12
• MongoDB 5.0: Versions 5.0.0 - 5.0.23
• MongoDB 4.4: Versions 4.4.0 - 4.4.28
• Older, end-of-life versions are also affected and will not receive patches.

Exploitation Status

Active exploitation has been confirmed. A public proof-of-concept (PoC) was released shortly after the disclosure, making it trivial for attackers to scan for and exploit vulnerable servers. Any publicly accessible MongoDB instance running an affected version with zlib compression enabled should be considered at extremely high risk of compromise.

Impact Assessment

The impact of MongoBleed is severe, despite being an information disclosure flaw rather than RCE:

• Credential Compromise: The primary risk is the leakage of plaintext credentials, API keys, and session tokens that are in the server's memory. This allows attackers to bypass authentication and gain legitimate, privileged access to databases and connected applications.
• PII Exposure: If the server is processing personally identifiable information (PII), fragments of this data could be leaked, leading to a data breach.
• Stepping Stone for Further Attacks: Armed with stolen credentials, an attacker can log into the database, exfiltrate entire collections, or pivot to attack other applications that trust the database server.
• System Reconnaissance: The memory leak could expose details about the server's configuration and internal architecture, aiding attackers in planning more sophisticated attacks.

Cyber Observables for Detection

Detecting exploitation requires monitoring for specific network patterns.

Detection & Response

D3FEND Reference: D3-NTA: Network Traffic Analysis

1. Network Intrusion Detection System (NIDS): Deploy NIDS signatures that are designed to detect the specific malformed MongoDB message structure used in the MongoBleed exploit. This is the most effective way to detect active attempts.
2. Firewall Log Analysis: Review firewall logs for connection attempts to your MongoDB instances from unexpected IP addresses. While not definitive proof of exploitation, it can indicate that your server is being targeted.
3. Assume Compromise: Given the unauthenticated nature of the exploit and the confirmation of active scanning, if you find a vulnerable, exposed server, you must assume that credentials have been compromised.

Mitigation

D3FEND Reference: D3-SU: Software Update, D3-CR: Credential Rotation

1. Upgrade Immediately (Priority 1): The primary mitigation is to upgrade to a patched MongoDB version:
   • 8.0.5 or newer
   • 7.0.11 or newer
   • 6.0.13 or newer
   • 5.0.24 or newer
   • 4.4.29 or newer
2. Workaround: Disable Zlib (If Upgrade is Impossible): If you cannot upgrade immediately, you can mitigate the vulnerability by disabling zlib network compression. This can be done by modifying the net.compression.compressors setting in your MongoDB configuration file to remove zlib and use other options like snappy or zstd.

   net:
     compression:
       compressors: snappy,zstd
   

3. Rotate All Credentials (CRITICAL): After upgrading or applying the workaround, you must rotate all credentials that could have been exposed. This includes database user passwords, application API keys, and any secrets stored in or accessed by applications connecting to the database. Failure to do this step leaves you vulnerable to an attacker who may have already stolen credentials.
4. Restrict Network Access: As a security best practice, MongoDB instances should not be exposed directly to the internet. Restrict access to a trusted set of application servers and administrative hosts using firewall rules.