Command Injection in Spring Boot with Dynamodb

Command Injection in a Spring Boot application that uses Amazon DynamoDB can occur when untrusted input is passed to system-level operations or to constructs that eventually reach an operating system shell. Although DynamoDB is a managed NoSQL service and does not execute shell commands, an application layer that builds dynamic queries, invokes scripts, or calls external processes can introduce injection points that bypass DynamoDB’s own safety mechanisms.

In Spring Boot, common patterns that may lead to Command Injection include using Runtime.getRuntime().exec() or ProcessBuilder with concatenated strings that incorporate user-controlled data, such as request parameters, headers, or DynamoDB attribute values. For example, if an attribute stored in DynamoDB (e.g., a file path or a system identifier) is later used to construct a shell command without proper validation or escaping, an attacker may inject additional shell operators and commands.

Consider a scenario where a DynamoDB table stores metadata about backup scripts, including a path or a host identifier. A Spring Boot service retrieves this item and uses it to invoke a local script via exec:

String scriptPath = item.get("scriptPath").getS();
String command = "/usr/local/bin/backup.sh " + scriptPath;
Process process = Runtime.getRuntime().exec(command);

If the scriptPath attribute is attacker-controlled (e.g., via a maliciously crafted DynamoDB entry or an API-supplied parameter), an input such as '; rm -rf / # could lead to arbitrary command execution. This specific combination is risky because DynamoDB itself does not validate how retrieved data is used downstream; the vulnerability resides in the application logic that interprets data as shell commands.

Another vector involves environment variables or system properties populated from DynamoDB items and later used by shell commands executed through Spring Boot’s integration with native tools or scripts. For instance, passing unsanitized input into a command that includes variable expansion increases the risk of breaking out of expected argument boundaries.

Even if DynamoDB Streams or Lambda triggers are used, the consumer code must avoid treating event data as safe. A Lambda function triggered by DynamoDB Streams that forwards record keys to a shell-based processing utility without input validation effectively propagates the risk of Command Injection.

To mitigate Command Injection when integrating Spring Boot with DynamoDB, avoid building shell commands from DynamoDB-derived data. Prefer using typed SDK calls and strict input validation. Below are concrete patterns and code examples that demonstrate secure handling.

1. Use the AWS SDK for Java v2 without shelling out

Instead of constructing shell commands, use the DynamoDB client directly to perform operations. This eliminates the command chain entirely:

DynamoDbClient ddb = DynamoDbClient.builder().region(Region.US_EAST_1).build();
GetItemRequest request = GetItemRequest.builder()
    .tableName("MyTable")
    .key(Map.of("id", AttributeValue.builder().s(requestedId).build()))
    .build();
Map item = ddb.getItem(request).item();

This approach ensures that data from DynamoDB is treated as structured data, not executable content.

2. Validate and sanitize before any external invocation

If external processes are unavoidable, perform strict allowlist validation on any DynamoDB-derived input. For example, if a script path is required, validate it against a predefined set of safe values:

Set allowedScripts = Set.of("backup.sh", "cleanup.sh");
String scriptName = item.get("scriptName").getS();
if (!allowedScripts.contains(scriptName)) {
    throw new IllegalArgumentException("Invalid script");
}
// Use a list-based exec form to avoid shell parsing
ProcessBuilder pb = new ProcessBuilder("/usr/local/bin/" + scriptName);
Process process = pb.start();

Using a list-based form of exec or ProcessBuilder prevents the shell from interpreting metacharacters, but the safest path is to avoid the shell altogether.

3. Avoid environment variables and system properties from untrusted sources

If environment variables must be set from DynamoDB values, sanitize them rigorously and avoid concatenation into command strings:

String safeValue = Pattern.compile("^[a-zA-Z0-9_\\-]+$").matcher(item.get("envValue").getS()).results()
    .map(MatchResult::group)
    .collect(Collectors.joining());
if (safeValue.isEmpty()) {
    throw new IllegalArgumentException("Unsafe environment value");
}
ProcessBuilder pb = new ProcessBuilder("mycommand");
pb.environment().put("SAFE_VAR", safeValue);
Process process = pb.start();

4. Secure downstream consumers of DynamoDB Streams

When using DynamoDB Streams with Lambda, treat event data as untrusted. Do not pass record keys or attributes directly to shell utilities. Validate and transform data within the Lambda runtime using safe libraries:

public class Handler implements RequestHandler {
    public Void handleRequest(DynamodbEvent event, Context context) {
        for (DynamodbEventRecord record : event.getRecords()) {
            String pk = record.getDynamodb().getKeys().get("pk").getS();
            // Process pk using SDK calls, not shell commands
        }
        return null;
    }
}

These patterns ensure that DynamoDB data remains within the managed data layer and does not become a conduit for operating system command execution.