A high-severity vulnerability in MongoDB has been disclosed that could allow unauthenticated attackers to read uninitialized heap memory from affected database servers.

Tracked as CVE-2025-14847 with a CVSS score of 8.7, the flaw stems from improper handling of length inconsistencies in Zlib-compressed protocol headers. While no exploitation has been confirmed publicly, the issue presents a serious risk of sensitive in-memory data exposure.

MongoDB has released patches across supported versions and urges administrators to upgrade immediately or apply mitigations if patching is not feasible.

Memory disclosure vulnerabilities remain a persistent risk in network-facing software, particularly in complex systems that handle compressed or encoded data.

In database platforms, even partial memory exposure can be dangerous. Heap memory may contain internal state information, memory pointers, or fragments of previously processed data. When such information is accessible without authentication, it can significantly weaken the security posture of an otherwise well-hardened environment.

MongoDB identified and disclosed a flaw affecting its server-side Zlib compression implementation.

The vulnerability allows a remote, unauthenticated client to send malformed compressed messages with mismatched length fields. When processed, the server may respond with portions of uninitialized heap memory.

The issue affects a wide range of MongoDB Server versions, including multiple releases across the 3.6 through 8.2 branches. MongoDB has confirmed the issue is fully resolved in patched releases, including 8.2.3, 8.0.17, 7.0.28, 6.0.27, 5.0.32, and 4.4.30.

At the core of the issue is length parameter inconsistency in Zlib-compressed protocol headers.

When the declared length of compressed data does not match the actual payload size, MongoDB’s server-side handling may fail to properly initialize memory buffers before responding to the client.

As a result, the server can inadvertently return heap memory that was never intended to be exposed. This memory may include remnants of previously allocated data structures, internal pointers, or operational metadata.

Importantly, this behavior occurs prior to authentication, making the flaw accessible to any network-reachable client.

While the vulnerability does not enable direct code execution, its impact should not be underestimated.

Exposure of heap memory can provide attackers with insights into server internals, memory layout, or application state. Such information is often leveraged as a stepping stone for more advanced attacks, including exploitation chaining or targeted denial-of-service efforts.

Organizations running publicly accessible MongoDB instances face the highest risk, particularly if compression is enabled and patching is delayed.

Unauthenticated memory disclosure vulnerabilities undermine fundamental trust boundaries.

Even in the absence of active exploitation, the existence of a remotely triggerable heap leak raises concerns about data confidentiality, compliance, and defense-in-depth assumptions. For enterprises relying on MongoDB for critical workloads, timely remediation is essential to maintaining security assurances.

Security firm OP Innovate emphasized that CVE-2025-14847 could expose sensitive in-memory data, including internal state and memory pointers.

MongoDB echoed this assessment, strongly recommending immediate upgrades. For environments where updates cannot be applied right away, MongoDB advises disabling Zlib compression and using alternative compressors such as Snappy or Zstandard.