CVE-2026-9754: MongoDB filemd5 Stack Memory Information Disclosure

Technical summary

This vulnerability stems from improper initialization of stack memory in MongoDB's filemd5 command handler. When an authenticated user with read-level privileges issues a malformed or specially crafted filemd5 command, the server may return portions of uninitialized stack memory in the response. This is a classic use-of-uninitialized-memory flaw (CWE-457) that occurs in a network-accessible command path. The CVSS 3.1 score of 6.5 reflects a network-based attack vector, low attack complexity, requirement for prior authentication and a read role, and a consequence limited to confidentiality breach with no impact to integrity or availability.

Business impact

The practical risk depends on what sensitive data might be present in MongoDB process memory at the time of exploitation. In environments where the database server runs alongside application logic, encryption keys, API tokens, or personally identifiable information could theoretically be leaked through repeated queries. The requirement for authenticated access and a read role limits the threat to insider threats, compromised application accounts, or authenticated network users. For most organizations, the impact is contained unless the MongoDB instance processes highly sensitive data and is accessible to untrusted authenticated users.

Affected systems

MongoDB (vendor: mongodb, product: mongodb) is affected. The vulnerability is present in versions prior to the patches released by MongoDB. Verify the exact affected version range and available patches against the MongoDB security advisory. All MongoDB deployments where authenticated users hold read roles should be considered potentially vulnerable until patched.

Exploitability

Exploitation requires valid database credentials with at least read role privileges and network access to the MongoDB instance. The attack is straightforward—an authenticated user simply issues specially crafted filemd5 commands—making it low complexity once authentication is gained. However, the requirement for pre-existing credentials means mass exploitation is unlikely; this is primarily an insider or post-compromise threat. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, indicating no widespread active exploitation has been reported.

Remediation

Apply the security patch released by MongoDB for CVE-2026-9754. Verify the patch version against the MongoDB security advisory. In addition, enforce the principle of least privilege by granting read role access only to users and applications that genuinely require it. Restrict network access to MongoDB instances using firewalls and VPN controls, and audit user activities and role assignments regularly.

Patch guidance

Contact MongoDB or consult the official MongoDB security advisory to determine the patched version(s) and your current version. Patch releases are typically cumulative and can be applied during a maintenance window. Test patches in a non-production environment first. If patching is delayed, compensate by tightening access controls and monitoring for suspicious filemd5 command usage.

Detection guidance

Monitor MongoDB logs and audit trails for unusual or repeated filemd5 command invocations, especially from read-role accounts. Network-based detection is difficult because filemd5 is a legitimate command; focus on behavioral anomalies such as high frequency, unusual parameters, or execution by service accounts that do not normally use this command. Intrusion detection signatures may be difficult to create given the low-level nature of the flaw; log analysis and role-based access reviews are more practical.

Why prioritize this

Although the CVSS score is medium (6.5) and active exploitation is not documented, this vulnerability should be patched in the normal maintenance cycle. The risk is elevated for organizations with sensitive data in MongoDB, strict insider threat concerns, or compliance requirements around data confidentiality. For general deployments, prioritize this below critical and high severity vulnerabilities but ahead of low-severity issues.

Risk score, explained

The CVSS 3.1 score of 6.5 reflects the combination of network accessibility (AV:N), low attack complexity (AC:L), mandatory authentication and read role requirement (PR:L), no user interaction (UI:N), and high confidentiality impact (C:H) but no integrity or availability impact (I:N/A:N). The score appropriately captures that this is a real information disclosure risk but mitigated by the authentication barrier and the limited scope of leaked data.

Frequently asked questions