CVE-2026-96747 MongoDB CVE debrief

Who should care

Defenders responsible for securing applications using PyMongo's client-side field level encryption (CSFLE) or Queryable Encryption should assess their exposure and verify the KMS endpoint configuration.

Why it matters

The vulnerability in PyMongo's handling of KMS endpoints allows an attacker with write access to the key vault collection to redirect the driver's KMS connection to an arbitrary Unix domain socket path on the application host, potentially leading to unauthorized connections.

• An attacker with write access to the key vault collection can redirect the driver's KMS connection to an arbitrary Unix domain socket path on the application host.
• The vulnerability allows for potential unauthorized connections to the application host.
• Defenders should verify the KMS endpoint configuration to prevent unauthorized connections.
• The vulnerability requires verification of the key vault collection security to prevent attackers from writing to it.

Technical summary

PyMongo passed the KMS endpoint of a data key verbatim into `parse_host()`, which returns any string ending in `.sock` unchanged instead of validating it as a hostname and port. This allows an attacker with write access to the key vault collection to redirect the driver's KMS connection to an arbitrary Unix domain socket path on the application host. The vulnerability can lead to unauthorized connections and potential security breaches. The issue affects applications using client-side field level encryption (CSFLE) or Queryable Encryption.

Defensive priority

Defenders should prioritize verifying the KMS endpoint configuration and ensuring that the key vault collection is properly secured.

Recommended defensive actions

• Verify the KMS endpoint configuration to prevent unauthorized connections.
• Ensure that the key vault collection is properly secured to prevent attackers from writing to it.
• Update PyMongo to version 4.18.2 or later to apply the fix.
• Review compensating controls for exposed systems while remediation is scheduled and verified.
• Check relevant monitoring, detection, and logs for exposed assets that need extra review.
• Track exceptions, retest remediated assets, and close the item only after evidence is documented.
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up.

Evidence notes

The vulnerability is caused by PyMongo passing the KMS endpoint of a data key verbatim into `parse_host()`, which returns any string ending in `.sock` unchanged instead of validating it as a hostname and port.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.