CVE-2025-6706: MongoDB Server Use-After-Free Vulnerability

CVE-2025-6706 Overview

CVE-2025-6706 is a use-after-free vulnerability [CWE-416] in MongoDB Server that allows an authenticated user to crash the database or trigger other unexpected behavior. The flaw resides in the Slot Based Execution (SBE) engine and is triggered when a user issues an aggregation framework operation containing a specific combination of rarely-used aggregation pipeline expressions. Exploitation does not require the privilege to shut down the server, so any authenticated principal with query rights can reach the vulnerable code path. The issue affects MongoDB Server 6.0 prior to 6.0.21, 7.0 prior to 7.0.17, and 8.0 prior to 8.0.4 when the SBE engine is enabled.

Critical Impact

An authenticated low-privilege user can crash MongoDB Server through a crafted aggregation pipeline, breaking confidentiality, integrity, and availability of the database service.

Affected Products

• MongoDB Server 6.0 versions prior to 6.0.21
• MongoDB Server 7.0 versions prior to 7.0.17
• MongoDB Server 8.0 versions prior to 8.0.4

Discovery Timeline

• 2025-06-26 - CVE-2025-6706 published to NVD
• 2025-09-15 - Last updated in NVD database

Technical Details for CVE-2025-6706

Vulnerability Analysis

The vulnerability is a use-after-free condition in MongoDB Server's aggregation framework when the SBE engine processes a query. SBE is MongoDB's newer query execution engine, designed to improve performance for aggregation pipelines. A specific combination of seldom-used aggregation pipeline stages and expressions causes the engine to reference memory that has already been released. Dereferencing freed memory can produce a server crash, but use-after-free conditions in C++ runtimes can also lead to memory disclosure or controlled write primitives depending on heap state at the time of reuse.

An authenticated attacker submits the malicious pipeline through a normal aggregate command. No elevated role is required, and the user does not need server shutdown permission. The resulting crash terminates the mongod process, breaking availability for every client connected to that node and triggering replica set failover events.

Root Cause

The root cause is improper lifetime management of an object within the SBE execution path. When the engine evaluates the offending pipeline expression combination, an internal reference outlives the underlying object, leaving a dangling pointer that is later dereferenced.

Attack Vector

Exploitation is performed over the network against the MongoDB wire protocol by any authenticated account that can run aggregation queries. The attacker constructs an aggregate command containing the triggering pipeline expressions and submits it against any database the account can read. Refer to the MongoDB Issue Tracker Entry for vendor-supplied technical context.

// No verified public proof-of-concept is available.
// The vulnerability is triggered by a specific combination
// of aggregation pipeline expressions processed by the
// SBE engine. See SERVER-106746 for vendor details.

Detection Methods for CVE-2025-6706

Indicators of Compromise

• Unexpected mongod process crashes or restarts correlated with client-issued aggregate commands.
• Replica set primary step-downs or failover events without an operational cause.
• Server logs containing fatal assertions or stack traces originating in SBE execution code.
• Repeated aggregation queries from a single authenticated user immediately preceding a crash.

Detection Strategies

• Audit MongoDB slow query and profiler logs for aggregation pipelines using uncommon expression combinations submitted by non-administrative accounts.
• Correlate mongod crash timestamps with the source IP and authenticated user of the last aggregation command processed.
• Inventory MongoDB deployments and flag any node running 6.0 < 6.0.21, 7.0 < 7.0.17, or 8.0 < 8.0.4 with SBE enabled.

Monitoring Recommendations

• Forward mongod logs, audit logs, and process supervisor events to a central SIEM for correlation.
• Alert on abnormal rates of replica set elections, connection resets, or aggregation command failures.
• Track per-user query patterns to surface accounts that suddenly issue complex aggregations they have never run before.

How to Mitigate CVE-2025-6706

Immediate Actions Required

• Upgrade MongoDB Server to 6.0.21, 7.0.17, 8.0.4, or later as appropriate for your release branch.
• Review and reduce the number of database users that hold aggregation privileges, applying least privilege.
• Rotate credentials for any service account whose query history shows suspicious aggregation activity.

Patch Information

MongoDB has released fixed builds in versions 6.0.21, 7.0.17, and 8.0.4. Patch and remediation details are tracked in the vendor advisory at the MongoDB Issue Tracker Entry.

Workarounds

• Disable the SBE engine on affected versions until the patch can be applied, since the crash path requires the SBE engine to be enabled.
• Restrict network access to mongod listeners so that only trusted application tiers can authenticate and submit queries.
• Enforce role-based access control and remove find or aggregation rights from accounts that do not require them.

# Example: disable the SBE engine via server parameter
# Apply to each mongod instance, then restart the service.
mongosh --eval 'db.adminCommand({ setParameter: 1, internalQueryFrameworkControl: "forceClassicEngine" })'

# Verify your server version after patching
mongosh --eval 'db.version()'