CVE-2026-11933: 
MongoDB vulnerability analysis and mitigation

CVE-2026-11933 is a use-after-free vulnerability in MongoDB Server's server-side JavaScript engine, triggered when converting BSON documents to JavaScript arrays. An authenticated user with read privileges who can execute server-side JavaScript (e.g., via $where or $function operators) can cause the server to access already-freed memory. Affected versions span multiple MongoDB release lines: 4.4.0–4.4.30, 5.0–5.0.33, 6.0–6.0.28, 7.0.0–7.0.36, 8.0.0–8.0.25, 8.2.0–8.2.10, and 8.3.0–8.3.3. The vulnerability was published on June 12, 2026, and carries a CVSS v4 base score of 8.7 (High) and a CVSS v3.1 base score of 8.8 (High) (GitHub Advisory, ENISA EUVD).

The root cause is a use-after-free condition (CWE-416, with an associated out-of-bounds write classification CWE-787) in MongoDB's server-side JavaScript engine during BSON-to-JavaScript array conversion. When a specially crafted BSON document is processed by the JavaScript engine, memory that has been freed is subsequently accessed, potentially allowing an attacker to read or corrupt heap memory. Exploitation requires network access and low-privilege authenticated credentials (read access), with no user interaction or special attack conditions needed. The vulnerability is reachable through MongoDB query operators that invoke server-side JavaScript, specifically $where and $function (GitHub Advisory, MongoDB Jira).

Successful exploitation can result in disclosure of sensitive information from the mongod process memory — potentially exposing credentials, query data, or other in-memory content — or a denial of service through a server crash. The impact is confined to the vulnerable MongoDB instance (no subsequent system impact), but memory disclosure could facilitate further attacks or data exfiltration. Availability of the database service may be fully disrupted if the server crashes (GitHub Advisory, ENISA EUVD).

1. Reconnaissance: Identify MongoDB instances running vulnerable versions (4.4.0–4.4.30, 5.0–5.0.33, 6.0–6.0.28, 7.0.0–7.0.36, 8.0.0–8.0.25, 8.2.0–8.2.10, or 8.3.0–8.3.3) using network scanning tools such as Shodan, Censys, or nmap targeting port 27017.
2. Authentication: Obtain or use existing low-privilege credentials (read access to any database collection is sufficient) to authenticate to the MongoDB instance.
3. Craft malicious query: Construct a MongoDB query using the $where or $function operator that passes a specially crafted BSON document designed to trigger the use-after-free condition during BSON-to-JavaScript array conversion in the server-side JS engine.
4. Trigger vulnerability: Submit the crafted query to the target MongoDB server. The server-side JavaScript engine processes the BSON document, frees memory, and then accesses the freed memory region.
5. Achieve objective: Depending on heap layout and timing, the attacker may read sensitive data from mongod process memory (e.g., credentials, query results, internal state) or cause the server to crash, resulting in denial of service (GitHub Advisory, MongoDB Jira).

• Logs: Unexpected mongod crashes or segmentation faults in MongoDB server logs (mongod.log); repeated errors related to JavaScript engine execution or BSON conversion failures; unusual $where or $function query patterns from non-administrative users in the MongoDB audit log.
• Process: Abnormal termination of the mongod process; core dump files generated in the MongoDB working directory following a crash.
• Network: Authenticated connections from unexpected source IPs submitting queries containing $where or $function operators to MongoDB port 27017; high-frequency query submissions from a single authenticated user targeting JavaScript-enabled operators.
• File System: Unexpected core dump files (e.g., core, core.mongod.<pid>) in the MongoDB data or working directory following a server crash.

MongoDB has released patched versions addressing this vulnerability; users should upgrade to versions beyond the affected ranges (i.e., 4.4.31+, 5.0.34+, 6.0.29+, 7.0.37+, 8.0.26+, 8.2.11+, or 8.3.4+) (ENISA EUVD). Percona Server for MongoDB users should consult Percona's security advisory for patched builds (Percona Blog). As a workaround prior to patching, restrict or disable server-side JavaScript execution by setting security.javascriptEnabled: false in the MongoDB configuration file (or using --noscripting at startup), which disables $where and $function operators. Additionally, limit read privileges to only trusted users and monitor for unusual server-side JavaScript activity.

Percona published a dedicated security advisory covering CVE-2026-11933 alongside CVE-2026-9740 for Percona Server for MongoDB, indicating vendor-ecosystem awareness and coordinated response (Percona Blog). A Reddit discussion in the MongoDB community referenced related MongoDB CVEs, reflecting community interest in the vulnerability class (Reddit). Security news outlet SecurityOnline.info and TheHackerWire covered the vulnerability shortly after disclosure (TheHackerWire).