Injection Flaws in Echo Go with Dynamodb

Injection flaws occur when untrusted data is sent to an interpreter as part of a command or query. In the context of an Echo Go service that uses the AWS SDK for DynamoDB, the risk arises when input from HTTP requests is directly interpolated into DynamoDB expressions or raw query parameters without proper validation or escaping.

DynamoDB itself does not use SQL, but it supports a JSON-based query language and condition expressions. When building these expressions by concatenating user-controlled values, developers can inadvertently create injection-like behavior. For example, an attacker may supply a parameter such as id with a value like 123 OR attribute_exists(aws:username) that is improperly embedded into a KeyConditionExpression or FilterExpression. Because Echo Go typically binds URL path parameters, query strings, or JSON payloads directly into DynamoDB API calls, malformed or malicious input can change the logical structure of the request.

Consider a handler that retrieves an item using a user-supplied partition key:

c := db.Query(&dynamodb.QueryInput{    TableName: aws.String("Users"),    KeyConditionExpression: aws.String("user_id = :uid"),    ExpressionAttributeValues: map[string]types.AttributeValue{        ":uid": &types.AttributeValueMemberS{Value: r.PathParam("user_id")},    },})

If the Echo route is defined as GET /users/:user_id, an attacker could send a request to /users/123%20AND%20attribute_exists(aws:username). If the server does not validate or sanitize user_id, the resulting expression becomes user_id = 123 AND attribute_exists(aws:username), which may return unintended items or expose metadata. This pattern is relevant to the BOLA/IDOR and Input Validation checks performed by middleBrick, which can detect whether untrusted input reaches DynamoDB expressions.

Additionally, injection-like issues can occur in scan operations where FilterExpression is built dynamically. For instance, concatenating a sort key value without parameterization can produce expressions that always evaluate to true, leading to excessive data retrieval and potential data exposure. middleBrick’s Data Exposure and Input Validation checks are designed to surface these risks by correlating runtime behavior with the OpenAPI specification.

Because Echo Go does not inherently sanitize inputs, the responsibility falls on the developer to validate and use safe construction patterns. middleBrick’s findings often reveal that what appears to be a simple key lookup can become a vector for logic manipulation when DynamoDB expressions are composed insecurely. Understanding this interaction helps teams write safer API code and avoid common pitfalls mapped to frameworks such as OWASP API Top 10.

To prevent injection-like issues in Echo Go with DynamoDB, use parameterized expressions and strict input validation. Never concatenate user input directly into query or filter expressions. Instead, rely on expression attribute values and validate input against expected patterns before use.

1. Use parameterized key condition expressions with strict type checking:

userId := r.PathParam("user_id")    if !isValidUserID(userId) {        return echo.ErrBadRequest    }    exprVals := map[string]types.AttributeValue{        ":uid": &types.AttributeValueMemberS{Value: userId},    }    out, err := db.Query(context.TODO(), &dynamodb.QueryInput{        TableName: aws.String("Users"),        KeyConditionExpression: aws.String("user_id = :uid"),        ExpressionAttributeValues: exprVals,    })

2. Validate input using allowlists. For identifiers, prefer UUID or numeric patterns:

func isValidUserID(id string) bool {    matched, _ := regexp.MatchString(`^[0-9a-f-]{36}$`, id)    return matched}

3. For filter expressions, prefer placeholders and avoid dynamic string assembly. If dynamic filtering is required, construct the expression safely:

// Build expression safely using known attribute names    attrName := "status"    // Ensure attrName is from a fixed set, not user input    filterExpr := aws.String(fmt.Sprintf("%s = :status", attrName))    out, err := db.Scan(context.TODO(), &dynamodb.ScanInput{        TableName: aws.String("Orders"),        FilterExpression: filterExpr,        ExpressionAttributeValues: map[string]types.AttributeValue{            ":status": &types.AttributeValueMemberS{Value: "shipped"},        },    })

4. Use middleware to normalize and validate path and query parameters before they reach handlers. Echo’s middleware can reject malformed input early:

func ValidateUserID(next echo.HandlerFunc) echo.HandlerFunc {    return func(c echo.Context) error {        id := c.Param("id")        if !isValidUserID(id) {            return echo.NewHTTPError(http.StatusBadRequest, "invalid user id")        }        return next(c)    }}

5. For operations that require dynamic expression building (such as admin tools), prefer using the DynamoDB ConditionExpression builder pattern rather than raw string concatenation, and log only sanitized representations.

By combining strict input validation, parameterized expressions, and safe construction patterns, teams can mitigate injection-related risks in Echo Go services that interact with DynamoDB. middleBrick can support this process by identifying insecure expression construction in the API spec and runtime behavior, enabling developers to address issues before deployment.