Integrity Failures in Echo Go with Dynamodb

An integrity failure occurs when an application fails to verify that data has not been improperly modified. In the combination of Echo Go and Amazon DynamoDB, this typically arises when application-layer logic does not enforce ownership or version checks before processing updates. Developers often construct update handlers that accept an ID and a payload, then directly call UpdateItem without ensuring the requesting user is authorized for that specific record. This gap enables BOLA/IDOR-style manipulation, where an attacker can change another user's resource simply by altering an identifier in the request.

DynamoDB's schema-less design amplifies this risk. Because items are stored as key-value maps, it is easy to omit an ownership attribute or to forget to validate it on read and write. For example, a developer might store user_id as part of the item but neglect to include it in the condition expression of an update. Without that condition, an attacker can submit a crafted request that updates the item while bypassing any intended user boundary. This is a classic integrity failure: the data changes, but the application incorrectly assumes the operation respects the intended scope.

The Echo framework adds another dimension to this pattern. Routes are often defined with path parameters such as /users/:userID/resources/:resourceID, and handlers parse these values directly into request context. If the handler retrieves the item from DynamoDB using only resourceID and then applies changes without re-confirming that the userID in the path matches the owner stored in the item, the system trusts the client-supplied path values. This trust is the root cause of many integrity flaws, because an attacker can iterate over plausible IDs and observe which succeed, leading to unauthorized modification or deletion of other users' data.

Real-world attack patterns mirror this structure. Consider an update endpoint that modifies a configuration object without checking a version or hash. An attacker could use a tool to replay modified requests, effectively tampering with state that should be immutable for other users. In systems that rely on DynamoDB conditional writes, omitting the condition or using an incorrect attribute name nullifies the safeguard. Additionally, if the application deserializes input into a loosely typed structure and then writes it back, injection of unexpected attributes can corrupt the item's integrity. These scenarios are not theoretical; they align with OWASP API Top 10 controls around BOLA and data integrity, and they map to broader compliance concerns such as PCI-DSS and SOC2 requirements for accurate data handling.

Instrumenting scans with middleBrick helps surface these patterns by correlating OpenAPI definitions with runtime behavior. The scanner checks whether update operations include proper authorization logic and whether responses expose sensitive details that could aid an attacker. While middleBrick does not fix the code, its findings highlight missing ownership checks and insufficient condition expressions in DynamoDB calls. By reviewing the scan output, teams can identify routes where path parameters flow into DynamoDB key expressions without strict validation, enabling developers to tighten the logic before an attacker exploits the weakness.

Remediation centers on enforcing ownership and version checks in every update operation. The safest approach is to treat the client-supplied ID as an input only, and to re-derive the item's key from authenticated context on each request. Use conditional update expressions that verify ownership attributes, and avoid constructing update expressions by string concatenation. Below are concrete Go examples that demonstrate a vulnerable pattern followed by a corrected implementation.

Vulnerable Pattern

An endpoint that accepts a resource ID from the URL and directly updates the item without verifying the authenticated user owns it:

// Assume echoContext is *echo.Context
// and userID is obtained from an auth middleware (but not re-validated)
resourceID := echoContext.Param("resourceID")
updateInput := &UpdateResourceInput{
    Name:  echoContext.Request().Body,
    UserID: userID, // taken from path or context, not verified against item
}
expr := &dynamodb.UpdateItemInput{
    TableName: aws.String("Resources"),
    Key: map[string]*dynamodb.AttributeValue{
        "resource_id": {S: aws.String(resourceID)},
    },
    UpdateExpression: aws.String("SET #name = :n, user_id = :uid"),
    ExpressionAttributeNames: map[string]*string{
        "#name": aws.String("name"),
    },
    ExpressionAttributeValues: map[string]*dynamodb.AttributeValue{
        ":n": {S: aws.String(updateInput.Name)},
        ":uid": {S: aws.String(updateInput.UserID)},
    },
    // Missing ConditionExpression to ensure ownership
}
_, err := dynamoClient.UpdateItem(context.TODO(), expr)

Corrected Implementation

Retrieve the item first to confirm ownership, then perform a conditional update. This ensures that the authenticated user matches the stored owner before any write occurs:

// Authenticated user ID from secure middleware
userID := ctx.Get("user_id").(string)
resourceID := echoContext.Param("resourceID")

// Fetch current item to validate ownership
var currentItem Resource
key := map[string]*dynamodb.AttributeValue{
    "resource_id": {S: aws.String(resourceID)},
}
getOut, err := dynamoClient.GetItem(context.TODO(), &dynamodb.GetItemInput{
    TableName:              aws.String("Resources"),
    Key:                    key,
    ConsistentRead:         aws.Bool(true),
})
if err != nil {
    // handle error
    return echo.ErrInternalServerError
}
if getOut.Item == nil {
    return echo.ErrNotFound
}

// Deserialize item and verify ownership
if err := dynamodbattribute.UnmarshalMap(getOut.Item, &currentItem); err != nil {
    return echo.ErrInternalServerError
}
if currentItem.UserID != userID {
    return echo.NewHTTPError(http.StatusForbidden, "access denied")
}

// Conditional update: ensure item has not changed since read
expr := &dynamodb.UpdateItemInput{
    TableName: aws.String("Resources"),
    Key: key,
    UpdateExpression: aws.String("SET #name = :n, version = version + :inc"),
    ConditionExpression: aws.String("user_id = :uid AND version = :ver"),
    ExpressionAttributeNames: map[string]*string{
        "#name": aws.String("name"),
    },
    ExpressionAttributeValues: map[string]*dynamodb.AttributeValue{
        ":n": {S: aws.String(updateInput.Name)},
        ":uid": {S: aws.String(userID)},
        ":inc": {N: aws.String("1")},
        ":ver": {N: currentItem.Version},
    },
}
_, err = dynamoClient.UpdateItem(context.TODO(), expr)
if err != nil {
    // Handle conditional check failures
    return echo.ErrConflict
}

Additional safeguards include using version numbers or hash-based attributes in condition expressions, avoiding publicly guessable IDs where feasible, and ensuring that any client-supplied filter in query operations includes the owner attribute. middleBrick can assist by flagging endpoints where update actions lack explicit ownership conditions in the associated specification, prompting developers to apply these patterns consistently.