attack-surface.md

Attack Surface Analysis for gin-gonic/gin

Attack Surface: Route Parameter Exploitation (Path Traversal & Injection)

• Description: Attackers manipulate URL parameters to access unintended resources or bypass security controls, specifically exploiting Gin's routing mechanisms.
  • Gin Contribution: Gin's wildcard and parameter routing (e.g., /users/:id, /files/*filepath) are vulnerable without robust input validation within the handler. Gin's routing logic itself does not perform content validation of the parameters. This is a direct consequence of how Gin handles routes.
  • Example: An attacker uses /users/../../etc/passwd with a route defined as /users/:id to attempt path traversal. Or, an attacker injects SQL code into a parameter if the handler uses it directly in a database query without proper escaping (though this is a general vulnerability, the entry point is Gin's parameter handling).
  • Impact: Unauthorized access to sensitive data, bypassing of security controls, potential code execution (if combined with other vulnerabilities like SQL injection).
  • Risk Severity: High to Critical (depending on the exposed data and functionality).
  • Mitigation Strategies:
    • Strict Input Validation (Within Handlers): Implement rigorous input validation inside each route handler. This is crucial because Gin does not validate parameter content. Check for path traversal sequences (.., /), unexpected characters, and data type/format violations.
    • Whitelist Allowed Characters: Define a whitelist of allowed characters for each parameter and reject any input containing characters outside the whitelist.
    • Sanitize Input: Sanitize input to remove or encode potentially dangerous characters, again, within the handler.
    • Avoid Overly Broad Wildcards: Use specific routes whenever possible. If wildcards are necessary, be extremely cautious with input validation.
    • Dedicated Path Traversal Middleware: Implement or use a middleware that specifically checks for and blocks path traversal attempts before they reach the route handler. This adds a layer of defense before Gin's routing logic.

Attack Surface: Mass Assignment (Data Binding)

• Description: Attackers inject unexpected fields into request payloads (JSON, XML, form data) to modify data they shouldn't have access to, directly exploiting Gin's binding features.
  • Gin Contribution: Gin's c.Bind, c.BindJSON, c.BindXML, etc., automatically bind request data to Go structs. This is the direct mechanism of the vulnerability. If the struct contains fields that should not be user-controlled, Gin will still bind them if present in the request.
  • Example: An attacker sends a JSON payload with an isAdmin field set to true when creating a user, hoping to gain administrative privileges. Gin will bind this field if it exists in the target struct.
  • Impact: Unauthorized modification of data, privilege escalation, data corruption.
  • Risk Severity: High to Critical (depending on the affected data).
  • Mitigation Strategies:
    • Use DTOs (Data Transfer Objects): Create separate structs specifically for request binding. Never directly bind to structs used for database interaction or other sensitive operations. This is the primary defense.
    • Whitelist Fields (Struct Tags): Use struct tags (e.g., json:"username,omitempty") to explicitly define which fields are allowed to be bound by Gin. This controls what Gin can bind.
    • Input Validation After Binding: Perform thorough input validation after Gin has performed the binding, to ensure data conforms to expected constraints. This is a secondary check.

Attack Surface: Denial of Service (DoS) via Large Payloads (Binding)

• Description: Attackers send excessively large request bodies to consume server resources, exploiting Gin's lack of default request size limits during binding.
  • Gin Contribution: Gin, by default, does not limit the size of request bodies when using c.Bind, c.BindJSON, etc. This is the direct enabler of the attack.
  • Example: An attacker sends a multi-gigabyte JSON payload to a route that uses c.BindJSON, causing the server to run out of memory.
  • Impact: Server resource exhaustion, application unavailability.
  • Risk Severity: High.
  • Mitigation Strategies:
    • Limit Request Body Size (Middleware): Use middleware to limit the maximum size of request bodies before they reach Gin's binding functions. Example: c.Request.Body = http.MaxBytesReader(c.Writer, c.Request.Body, 1024*1024) (for a 1MB limit). This is the primary defense.
    • Streaming (for very large files): If you must handle very large files, consider using streaming techniques instead of relying on Gin's binding to load the entire request body into memory.

Attack Surface: Untrusted Proxy Header Spoofing

• Description: Attackers manipulate proxy headers (e.g., X-Forwarded-For) to spoof their IP address, bypassing security controls that rely on IP addresses.
  • Gin Contribution: While Gin doesn't trust these headers by default, if gin.SetTrustedProxies is misconfigured (especially with nil), Gin will use the attacker-supplied values. This is a direct configuration issue within Gin.
  • Example: An attacker sets X-Forwarded-For to a trusted IP address to bypass IP-based restrictions that are implemented using Gin's request context information.
  • Impact: Bypassing IP-based restrictions, manipulating logging, potentially gaining unauthorized access.
  • Risk Severity: High (if proxy headers are incorrectly trusted).
  • Mitigation Strategies:
    • Only Trust Known Proxies: Only enable trust for proxy headers if your application is actually behind a trusted proxy and you understand the implications.
    • Use gin.SetTrustedProxies Correctly: Explicitly specify which proxy IP addresses or networks are trusted using gin.SetTrustedProxies. Never use gin.SetTrustedProxies(nil) in a production environment, as this trusts all proxies.