Security Intelligence
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At a glance: A newly disclosed vulnerability in MongoDB Server, tracked as CVE‑2025‑14847, places organizations running unpatched instances at elevated risk, particularly when the service is reachable from untrusted networks. Rapid patching, strict network access controls, and disabling Zlib compression when upgrades are delayed are recommended to reduce exposure. Although the vulnerability does not provide full database access or remote code execution, it enables unauthenticated attackers to extract sensitive memory fragments that may support follow‑on attacks.
Threat summary
On 24 December 2025, new reporting detailed a vulnerability in MongoDB Server. MongoDB is a widely deployed NoSQL database platform used for application backends, analytics workloads, and distributed data services. The vulnerability affects nearly all major MongoDB Server branches released since version 3.6, including all versions of 4.0 and 4.2, and all unpatched releases of 4.4, 5.0, 6.0, 7.0, 8.0, and 8.2.
The flaw, tracked as CVE‑2025‑14847, involves improper handling of mismatched length fields in Zlib‑compressed protocol headers. Zlib is a widely used compression library that reduces the size of data sent over the network. Each compressed message includes a header that tells the server how to decompress the data, including expected lengths. In this case, MongoDB trusted these length values. When an attacker sends a message with incorrect or mismatched length fields, the server’s decompression logic can become confused and return uninitialized heap memory instead of valid data.
An unauthenticated remote client can exploit this by opening a simple Transmission Control Protocol (TCP) connection to the MongoDB service port and sending a crafted compressed message. Establishing such a connection is trivial for any remote party with network reachability, and threat actors routinely scan the internet for exposed database ports. The attacker cannot control which memory fragments are returned, but repeated requests can reveal leftover data from the server’s working memory. These fragments may include pieces of previous operations, internal state information, or sensitive material not meant to be exposed. The Common Vulnerability Scoring System v4.0 score is 8.7 (High).
The worst‑case scenario involves an attacker repeatedly exploiting the flaw to gather enough leaked memory fragments to recover sensitive information. These fragments may include pieces of previous queries, authentication‑related data, internal state information, or portions of cryptographic material. While the vulnerability does not directly grant full database access or remote code execution, the leaked data can reveal secrets that enable more advanced follow‑on attacks. Over time, this can escalate into unauthorized access, impersonation, or bypassing security controls that rely on the confidentiality of those values.
MongoDB released patched versions across all supported branches, including 8.2.3, 8.0.17, 7.0.28, 6.0.27, 5.0.32, and 4.4.30.
Insights & mitigations
Mitigations include upgrading to the patched MongoDB Server versions released in December 2025. For environments where immediate upgrades are not possible, MongoDB’s official workaround recommends disabling Zlib compression on the server by starting mongod or mongos with a networkMessageCompressors or net.compression.compressors setting that omits Zlib. Safe values include snappy, zstd, or disabled. Restricting network access to MongoDB ports through firewall rules, private network segmentation, or virtual private networks further reduces exposure. Reviewing deployments for unintended internet reachability and monitoring for anomalous connection attempts to MongoDB ports are recommended.
Field Effect MDR users will be alerted via ARO if exposed servers are detected in their environment.
Field Effect MDR reduces the risk of exploitation by providing continuous network visibility, asset discovery, and behavioral analytics help surface early indicators of probing or exploitation attempts.
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