Key Range Buffer Overflow in MongoDB with Aggregation Pipeline

CVE-2026-9749

What is CVE-2026-9749?

A vulnerability exists in MongoDB's aggregation pipeline that can lead to a buffer overflow when using the internal $exchange stage set with key-range partitioning. If a single key range generates a substantial number of documents filling the exchange buffer, the server encounters a condition where it incorrectly detects a full per-consumer buffer. However, the internal 'high watermark' for that specific key range remains unchanged, potentially leading to resource exhaustion or unexpected behavior during data processing.

References