CVE-2026-1847 is a vulnerability classified under CWE-770 (Allocation of Resources Without Limits or Throttling) affecting MongoDB Server versions 7.0 and 8.0. The issue arises when certain large documents are inserted into a MongoDB replica set. In such cases, the secondary nodes in the replica set may fail to fetch the oplog (operation log) from the primary node. The oplog is critical for replication consistency and synchronization across the replica set. When secondaries cannot fetch the oplog, replication stalls, which can cascade into server instability and ultimately cause the MongoDB server to crash. This vulnerability impacts the availability of the database service by disrupting replication processes. The CVSS 4.0 vector indicates network attack vector (AV:N), low attack complexity (AC:L), no privileges required (PR:L - low privileges), no user interaction (UI:N), and high impact on availability (VA:H) with no impact on confidentiality or integrity. The vulnerability does not require user interaction but does require some level of privileges on the database server. No patches were listed at the time of this report, and no known exploits have been observed in the wild. The vulnerability highlights a lack of resource throttling or limits when handling large document insertions, which can be exploited to degrade or deny service by exhausting replication resources.

For European organizations, the impact of CVE-2026-1847 can be significant, especially for those relying on MongoDB replica sets for critical applications such as financial services, healthcare, government services, and large-scale web platforms. The stalling of replication and potential server crashes can lead to downtime, data unavailability, and disruption of dependent services. This can affect business continuity, cause financial losses, and damage reputation. In regulated industries, such outages may also lead to compliance violations. The vulnerability primarily affects availability, but prolonged replication issues could indirectly impact data integrity if failover mechanisms are improperly handled. Organizations with distributed MongoDB deployments across multiple data centers or cloud environments may experience cascading failures if replication stalls are not detected and mitigated promptly.

1. Monitor MongoDB replica set health continuously, focusing on replication lag and oplog fetching status to detect early signs of replication stalls. 2. Implement strict limits on document sizes at the application or database level to prevent insertion of excessively large documents that could trigger the vulnerability. 3. Restrict database user privileges to the minimum necessary to reduce the risk of exploitation by low-privilege users. 4. Deploy rate limiting or throttling mechanisms on write operations to prevent resource exhaustion from large document insertions. 5. Prepare incident response plans for rapid failover or recovery in case of replication failure or server crashes. 6. Stay updated with MongoDB vendor advisories and apply patches or updates as soon as they become available to address this vulnerability. 7. Consider architectural adjustments such as sharding or splitting large documents to reduce the risk of triggering replication stalls. 8. Use network segmentation and firewall rules to limit exposure of MongoDB servers to untrusted networks.