MongoDB $exchange Stage Buffer Update Failure Enables DoS
CVE-2026-9749 Published on June 9, 2026
Using MaxKey() may crash the server
This issue can occur when running an aggregation pipeline that uses the internal $exchange stage configured with key-range partitioning and order-preserving delivery. If a single key range produces enough documents to fill its exchange buffer (that is, many results are routed to the same consumer), the server reaches the code path where a full per-consumer buffer is detected but the internal "high watermark" for that key range is not updated as intended.
Vulnerability Analysis
CVE-2026-9749 can be exploited with network access, and requires small amount of user privileges. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality and integrity, and a high impact on availability.
Weakness Type
What is an assertion failure Vulnerability?
The product contains an assert() or similar statement that can be triggered by an attacker, which leads to an application exit or other behavior that is more severe than necessary.
CVE-2026-9749 has been classified to as an assertion failure vulnerability or weakness.
Products Associated with CVE-2026-9749
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Affected Versions
MongoDB Server:- Version 8.3.0 and below 8.3.3 is affected.
- Version 8.2.0 and below 8.2.10 is affected.
- Version 8.0.0 and below 8.0.24 is affected.
- Version 7.0.0 and below 7.0.35 is affected.