Security

Mongobleed PoC Leaks Memory via MongoDB zlib Bug

Mongobleed PoC Exploit for MongoDB CVE-2025-14847
Memory Leak

• Key Takeaways:

  • A public PoC called “mongobleed” exploits CVE-2025-14847, a memory-leak in MongoDB’s zlib decompression.
  • Attackers can extract uninitialized server memory without authentication, exposing logs, /proc data, connection UUIDs and client IPs.
  • Affected branches include MongoDB 5.0–8.2; fixes are available (see versions 5.0.32, 6.0.27, 7.0.28, 8.0.17, 8.2.3).
  • Immediate actions: apply patches, disable unauthenticated access, and monitor port 27017 for anomalous scans.

What is Mongobleed?

Mongobleed is a Python-based proof-of-concept (PoC) exploit published on GitHub that targets CVE-2025-14847. Its author, Joe Desimone, released the code to demonstrate how a decompression bug can be used to “bleed” sensitive memory from running MongoDB instances.

The flaw affects how MongoDB processes compressed messages that use zlib. Attackers can trigger server-side allocation of oversized buffers and then read uninitialized portions as BSON data.

How the exploit works

An attacker sends a specially crafted compressed message claiming an inflated uncompressedSize. MongoDB allocates a large buffer based on that claim, but zlib decompresses only the provided data into the buffer's start.

Because the server treats the whole buffer as valid, BSON parsing interprets uninitialized memory as field names until null bytes appear. As Desimone explains in the repo, “Mongobleed systematically scans memory regions by crafting malformed BSON documents with varying length fields.”

Observed leaked data

Proofs in the repo show fragments such as WiredTiger configuration, /proc/meminfo entries (e.g., "MemAvailable"), Docker paths, connection UUIDs and client IPs, and TCP counters like SyncookiesFailed.

Affected versions and fixes

MongoDB branches affected include 5.0.x through 8.2.x. Upstream fixes were released in these versions: 5.0.32, 6.0.27, 7.0.28, 8.0.17 and 8.2.3. MongoDB’s upstream commits validate decompressed lengths before buffer processing to block the leak.

Tool details and reproduction

The PoC is a simple Python script. Basic usage scans offsets 20–8192:

python3 mongobleed.py --host

Deeper scans extend to ~50,000 offsets and write leaked memory to a binary file. The author also provides a Docker Compose test setup to reproduce findings locally. Repo: https://github.com/joe-desimone/mongobleed

Recommendations

Apply the vendor patches immediately on exposed instances and follow defense-in-depth: disable unauthenticated access, require authentication and TLS, restrict access to port 27017 with network controls, and monitor logs for scanning patterns.

Quick mitigation steps

  • Patch to the fixed MongoDB releases listed above.
  • Block or firewall port 27017 from untrusted networks.
  • Audit deployments in cloud and container environments for outdated MongoDB versions.

OX Security first disclosed the bug; Desimone’s public PoC aims to accelerate awareness. Organizations should treat this as a high-priority remediation and hunt for signs of exploitation in logs and network telemetry.

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