Full Report
TL;DR: I found a cool way to get rid of pre-conditions in NOSQL syntax injections
Analysis Summary
# Vulnerability: MongoDB Syntax Injection Technique to Bypass Query Pre-conditions
## CVE Details
- CVE ID: N/A (This appears to be new research/technique disclosure rather than a specific, patched vendor vulnerability. No CVE was assigned in the source material.)
- CVSS Score: N/A
- CWE: CWE-843: Access of Object Member in its assumed type error (Related to improper use of JavaScript evaluation context, potentially CWE-94: Improper Control of Generation of Code ('Code Injection') in context of `$where` clause)
## Affected Systems
- Products: MongoDB (specifically database queries utilizing JSON filter syntax and the `$where` clause)
- Versions: Unspecified, but generally affects MongoDB instances supporting the documented query syntax patterns (i.e., versions prior to any potential defensive mitigation for these specific injection patterns).
- Configurations: Applications that construct MongoDB query filters using unsanitized user input, particularly those relying on string concatenation or interpolation.
## Vulnerability Description
The research details two primary methods for NoSQL (specifically MongoDB) injection: Operator Injection (limited to the field being injected) and Syntax Injection (allowing alteration of the query structure).
The core finding focuses on bypassing **pre-conditions** embedded in JSON query filters when syntax injection is possible:
1. **In `$where` clauses:** Exploiter can use JavaScript logic (e.g., `this.username=='...' || 1`) alongside careful string termination handling (e.g., using `||1%00` or `||'x'`) to force evaluations to `true`, bypassing pre-existing filter conditions on other fields or complex JavaScript logic.
2. **In JSON Filter Syntax:** When injecting into a specific field value (e.g., `{"username": "INJECT_HERE"}`), the attacker can close the initial string delimiter (`"`) and inject subsequent, structure-altering key/value pairs. The trailing quote from the original input is bypassed by:
* Adding a benign key/value pair and omitting its closing quote (e.g., `,"status":"active`).
* A superior method: Injecting a `$where` clause that evaluates to true (e.g., `,"$where":"1"`) to neutralize the trailing quote/structure error.
The attacker notes that **post-conditions** (conditions defined *after* the injection point in the filter, e.g., a password hash) are generally not bypassable due to MongoDB's "last value wins" behavior for duplicate keys.
## Exploitation
- Status: PoC available (The article clearly outlines several functional exploitation payloads.)
- Complexity: Medium (Requires specific knowledge of MongoDB query structure and JavaScript evaluation quirks within `$where`.)
- Attack Vector: Network (If input is taken remotely via an application layer).
## Impact
- Confidentiality: High (If the injection allows retrieval of all documents regardless of pre-conditions.)
- Integrity: High (If the injection allows modification of filter logic, potentially leading to unintended data manipulation or validation bypasses if the application layer relies on these conditions.)
- Availability: Medium (Potential for denial of service via complex or resource-intensive queries, though the goal described is data retrieval.)
## Remediation
### Patches
- No specific vendor patches are cited as this is a research disclosure on technique. Mitigation must be applied by application developers.
### Workarounds
- **Input Validation & Sanitization:** Rigorously validate and sanitize all user-supplied input destined for MongoDB query construction. Treat input as pure data, never executable code or structural elements.
- **Use of Parametrized Queries/APIs:** Utilize MongoDB driver features that abstract query construction, ensuring user input is always treated as literal values rather than executable query components. Avoid dynamic string concatenation for query building entirely, especially where `$where` is involved.
- **Remove `$where` Clause Usage:** Disable or prohibit the use of the `$where` operator in production environments, as it allows arbitrary JavaScript execution against documents.
## Detection
- **Monitoring for `$where` Usage:** Flag any database access logs or query strings containing the literal string `"$where":` or JavaScript evaluation syntax.
- **Payload Signatures:** Monitor for injection payloads designed to bypass string termination, such as the appearance of specific logical operators (`||1`, `%00`, or unexpected structural closers like `","status":`).
- **Resource Profiling:** Excessive or unusually large query result sets returned from a function previously restricted by pre-conditions could indicate successful injection.
## References
- Analyst Blog Post detailing MongoDB injection bypass techniques. (No external links provided in source)