ISSUE SUMMARY
There is a risk of in-memory corruption on MongoDB 4.2.7 when incremental backup is enabled.

USER IMPACT
For this bug to occur:

• The deployment must be running MongoDB 4.2.7.
• The deployment is managed by Ops Manager 4.2.13+ or managed in Cloud Manager with MongoDB agent version v10.14.0+.
• Incremental backups are enabled.
• The deployment has collection files larger than 2GB on disk.
• These collections are modified anytime after backups are enabled.

If these conditions are met (and only if all these conditions are met), there is a chance that MongoDB will improperly overwrite memory. The most likely results of this bug are failed operations or process crashes. It is possible that a document in memory may be corrupted in a way that allows it to be returned to a client or persisted to disk without an explicit failure.

SUGGESTED ACTION
All users on MongoDB 4.2.7 with incremental backup should upgrade to MongoDB 4.2.8 to avoid encountering this issue. If you have experienced a process crash and your deployment meets the above conditions, it may be advisable to validate the collections on the process to ensure that the data is consistent.

AFFECTED VERSIONS
This issue affects version 4.2.7.

FIX VERSION
The fix is included in 4.2.8.