CVE-2026-82059 Overview
CVE-2026-82059 is a denial-of-service vulnerability in MongoDB Server caused by an internal aggregation expression that was incorrectly exposed to any authenticated user. The expression was intended for internal cluster operations but was registered as generally accessible. An authenticated user with read-only privileges can supply a malformed index specification to this expression and trigger an assertion failure in the index key generation code path. In certain build configurations, the assertion terminates the mongod process and disconnects all clients. The issue is classified under CWE-617: Reachable Assertion.
Critical Impact
Any authenticated read-only user can crash the mongod process, causing service-wide denial of service for all connected clients.
Affected Products
- MongoDB Server (see MongoDB SERVER-130571 for affected versions)
- Deployments where authenticated users hold read-only or higher database privileges
- Build configurations where assertion failures terminate the server process
Discovery Timeline
- 2026-09-08 - CVE-2026-82059 published to the National Vulnerability Database (NVD)
- 2026-09-08 - Last updated in NVD database
Technical Details for CVE-2026-82059
Vulnerability Analysis
The flaw sits at the intersection of access control and input validation. MongoDB exposes aggregation expressions to users through the aggregation pipeline framework. A subset of these expressions is reserved for internal cluster communication and coordination. One such internal expression was registered in the general expression parser table with permissions allowing invocation by any authenticated session.
When invoked, the expression forwards its argument into the index key generation subsystem. The subsystem enforces structural invariants on index specifications through runtime assertions. Supplying a malformed specification violates those invariants and triggers an unrecoverable assertion, described in [CWE-617]. In builds compiled with fatal assertion handling, the failure aborts the mongod process rather than returning an error to the caller. Every connected client is disconnected, replica set members must re-elect, and sharded clusters lose the affected shard until the process restarts.
Root Cause
The root cause is an incorrect access classification. The internal aggregation expression should have been restricted to intra-cluster contexts, such as replication and sharding traffic authenticated with cluster credentials. Instead, it was registered with a permission scope reachable by ordinary authenticated users. The downstream index key generation code assumes callers have already validated the specification, so it uses assertions rather than graceful error handling to enforce invariants.
Attack Vector
Exploitation requires network access to a MongoDB instance and valid credentials for any account with basic read privileges. The attacker issues an aggregation command that references the internal expression and embeds a crafted, malformed index specification as its argument. The server accepts the command, dispatches to the index key generator, and hits the assertion. No user interaction is required. The attack does not compromise confidentiality or integrity; it only affects availability, but the impact spans every client connected to the process. Refer to MongoDB SERVER-130571 for the technical details tracked by the vendor.
Detection Methods for CVE-2026-82059
Indicators of Compromise
- Unexpected mongod process termination with assertion failure entries in the server log
- Aggregation commands from non-administrative users that reference undocumented or internal-only expression operators
- Client-side connection resets across all applications talking to a single MongoDB node at the same instant
- Replica set elections or shard failovers not correlated with maintenance activity
Detection Strategies
- Parse mongod logs for fatal assertion messages emitted from index key generation paths and correlate with the invoking session's authentication context
- Enable database auditing and alert on aggregation commands containing unusual or internal-scope expression names issued by non-system accounts
- Baseline aggregation traffic per user role and flag deviations from read-only accounts issuing complex expression arguments
Monitoring Recommendations
- Track mongod uptime, unclean shutdown counters, and replica set election frequency as availability signals
- Forward MongoDB audit logs and process-lifecycle events into a centralized SIEM for cross-node correlation
- Monitor authentication events for read-only accounts that begin issuing aggregation workloads outside their historical patterns
How to Mitigate CVE-2026-82059
Immediate Actions Required
- Apply the MongoDB Server update referenced in SERVER-130571 as soon as a fixed build is available for your release train
- Audit database user roles and remove read privileges from accounts that do not require them
- Restrict network reachability of mongod to trusted application subnets using firewall rules or private networking
- Rotate credentials for any account that shows anomalous aggregation activity
Patch Information
MongoDB tracks the fix under Jira issue SERVER-130571. The remediation reclassifies the affected internal aggregation expression so that it is only accessible in internal cluster contexts and adds input validation to reject malformed index specifications before they reach the assertion. Administrators should upgrade to the patched point release for their supported MongoDB Server major version.
Workarounds
- Enforce least-privilege role assignment so untrusted or application-tier accounts do not hold database-wide read privileges
- Place MongoDB behind an authenticating proxy or query router that rejects aggregation pipelines referencing internal expressions
- Enable replica set deployments with automatic failover to reduce downtime if a node is crashed by exploitation
- Disable direct client access to secondary and arbiter nodes to limit the exposed attack surface
# Configuration example: enforce authentication, TLS, and bind to private interfaces
security:
authorization: enabled
clusterAuthMode: x509
net:
bindIp: 10.0.0.10
tls:
mode: requireTLS
certificateKeyFile: /etc/ssl/mongod.pem
setParameter:
auditAuthorizationSuccess: true
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
