Radware’s Cyber Threat Intelligence (CTI) team is monitoring the active exploitation of CVE-2025-14847, nicknamed "MongoBleed." This critical vulnerability affects the zlib decompression logic in MongoDB, allowing unauthenticated attackers to extract sensitive data from server memory remotely [1].
Key Attack Insights:
- Unauthenticated Data Exfiltration: The vulnerability resides in the wire protocol compression layer, specifically within the zlib library integration. It allows attackers to trigger a memory leak by sending malformed, compressed network packets without requiring valid credentials or user interaction. [2]
- Widespread Impact and Active Exploitation: The flaw affects multiple major versions of MongoDB Server. Research indicates that 42% of cloud environments contain at least one vulnerable instance, and proof-of-concept (PoC) exploits are currently being used in the wild [2]
- Distinct Behavioral Signatures: Exploitation attempts leave a specific forensic footprint in server logs. Attacks are characterized by high-velocity connection bursts that lack standard client metadata events, distinguishing them from legitimate application traffic. [3]
Figure 1: CVE-2025-14844 – a high-severity disclosure vulnerability in MongoDB’s zlib decompression logic (source: Gemini)
Background
Disclosed in late December 2025, CVE-2025-14847 has been assigned a CVSS v4.0 severity score of 8.7 (High). The vulnerability, compared by researchers to the infamous "Heartbleed" bug, impacts the availability and confidentiality of data residing in MongoDB instances.[3]
Because the flaw exists in the pre-authentication phase of the connection handling, any internet-exposed MongoDB server with zlib compression enabled is immediately at risk. Attackers can exploit this to scrape credentials, session tokens, and Personally Identifiable Information (PII) directly from the heap memory.[1]
The Flaw: Zlib Decompression Mishandling
The root cause of MongoBleed is a logic error in MongoDB's handling of decompressed data lengths. Specifically, the vulnerability exists within the message_compressor_zlib.cpp file. [2]
When a client sends a compressed message, the server attempts to decompress it. In vulnerable versions, the code incorrectly returned the size of the allocated buffer (output.length()) rather than the actual length of the decompressed data. By sending a specially crafted, undersized packet, an attacker can force the server to respond with a buffer that includes the decompressed payload, along with adjacent, uninitialized heap memory. This "over-read" is returned to the attacker, thereby leaking any sensitive data that happens to reside in that memory space.[4]
Affected Versions The vulnerability spans years of MongoDB releases. The following versions are confirmed vulnerable: [1]
- 8.2.x: 8.2.0 - 8.2.2
- 8.0.x: 8.0.0 - 8.0.16
- 7.0.x: 7.0.0 - 7.0.27
- 6.0.x: 6.0.0 - 6.0.26
- 5.0.x: 5.0.0 - 5.0.31
- 4.4.x: 4.4.0 - 4.4.29
- Legacy Versions: All versions of 4.2, 4.0, and 3.6 are vulnerable and, as of this writing, have no patch available.
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Reasons for Concern
Radware’s CTI team identifies several factors that elevate the risk level of this vulnerability:
- Zero-Authentication Barrier: Unlike many exploits that require prior access or valid credentials, this vulnerability allows any remote attacker to read server memory anonymously. This "pre-authentication" nature makes it trivial for threat actors to scrape API keys and passwords necessary for lateral movement.
- Legacy Debt and Unpatchable Systems: While patches exist for newer versions, widely deployed End-of-Life (EOL) versions—specifically 3.6, 4.0, and 4.2—remain permanently vulnerable with no fix available. Organizations running these legacy systems must rely solely on mitigation strategies like disabling compression or network isolation.
- Detection Blind Spots: The exploit is primarily detectable via MongoDB server logs, which many organizations do not forward to a central SIEM. Furthermore, identifying the attack requires complex logic—monitoring for "silent" connections that lack metadata and exhibit extreme velocity—which is challenging to implement in standard signature-based detection engines.
What to search for in the logs?
While patching is the primary defense, log analysis is critical for identifying past or ongoing exploitation. Logs can identify active exploitation through two specific anomalies:
- Absence of Client Metadata: Legitimate MongoDB drivers (Node.js, PyMongo, etc.) automatically send a "client metadata" handshake immediately after connecting (Event ID 51800). The current MongoBleed exploit connects (Event ID 22943) and disconnects (Event ID 22944) without ever sending this metadata. A metadata rate of 0% across multiple connections is a high-fidelity indicator of attack.
- High-Velocity Bursts: Legitimate traffic typically generates persistent connections or lower connection rates (e.g., single digits per minute). To effectively scrape memory, attackers must rapidly establish tens of thousands of connections. Forensic analysis of attack traffic has shown velocities exceeding 111,000 connections per minute, compared to legitimate production traffic of roughly 0.2 to 3.2 connections per minute.
Recommandations
Radware recommends organizations take immediate steps to secure their data infrastructure:
Patch Immediately: Upgrade to the fixed versions released by MongoDB: 8.2.3, 8.0.17, 7.0.28, 6.0.27, 5.0.32, or 4.4.30.
- Disable Compression (Workaround): If immediate patching is not feasible, or if running end-of-life versions (4.2 and older), disable zlib compression in the configuration. This can be done by omitting zlib from networkMessageCompressors or net.compression.compressors.
- Network Segmentation: Ensure MongoDB instances are not exposed to the public internet. Use firewalls and VPNs to restrict access solely to trusted application servers.
- Forensic Review: Utilize tools like Velociraptor or SIEM queries to hunt for the specific log patterns described above (High connection count + Zero metadata events) to determine if data was exfiltrated prior to patching.
Resources List
[1] Eric Capuano, "Hunting MongoBleed (CVE-2025-14847)," Eric’s Substack, December 27, 2025. https://blog.ecapuano.com/p/hunting-mongobleed-cve-2025-14847
[2] Wiz Research Team, "MongoBleed (CVE-2025-14847) exploited in the wild," Wiz Blog, December 28, 2025. https://www.wiz.io/blog/mongobleed-cve-2025-14847-exploited-in-the-wild-mongodb
[3] National Vulnerability Database, "CVE-2025-14847 Detail," NIST, December 19, 2025. https://nvd.nist.gov/vuln/detail/CVE-2025-14847
[4] OX Research Team, "MongoDB Unauthenticated Attacker Sensitive Memory Leak," OX Security, December 24, 2025. https://www.ox.security/blog/attackers-could-exploit-zlib-to-exfiltrate-data-cve-2025-14847/