How to fix Improper Error Handling
in Poem
Executive Summary
Improper error handling in Poem allows attackers to fingerprint your stack by leaking internal logic, database schemas, or environment details via raw 500 responses. In Rust, the '?' operator is convenient but dangerous if your internal error types implement 'IntoResponse' by dumping their debug representation. To secure a Poem application, you must implement a sanitization layer that maps internal failures to generic, safe HTTP responses.
The Vulnerable Pattern
use poem::{handler, web::Path, Result, error::InternalServerError};#[handler] async fn get_data(Path(id): Path(String)) -> Result
{ // VULNERABILITY: Directly leaking internal DB error messages to the client let db_error = format!(“Query failed: SELECT * FROM secrets WHERE id = ’{}’. Connection to 192.168.1.50 timed out.”, id); // InternalServerError here serializes the string directly into the response body Err(InternalServerError(db_error))
}
The Secure Implementation
The vulnerable snippet uses Poem's default error helpers to pass raw strings back to the client, which often contains sensitive infrastructure metadata. The secure version uses a custom error enum with the 'thiserror' crate and implements Poem's 'ResponseError' trait. This creates a hard boundary: internal errors are logged to stderr for developers, while the 'as_response' method ensures the client only receives a sanitized, non-descriptive error message and a generic status code. This prevents information disclosure and aids in maintaining a clean security posture.
use poem::{handler, web::Path, Response, IntoResponse, error::ResponseError, http::StatusCode}; use thiserror::Error;#[derive(Error, Debug)] enum AppError { #[error(“Internal Database Error”)] DbFail(String), }
// Implement ResponseError to sanitize the output impl ResponseError for AppError { fn as_response(&self) -> Response { match self { // Log the actual error internally, but return a generic message to the user AppError::DbFail(internal_msg) => { eprintln!(“LOG [CRITICAL]: {}”, internal_msg); Response::builder() .status(StatusCode::INTERNAL_SERVER_ERROR) .body(“An unexpected error occurred. Reference ID: ERR-500”) } } } }
#[handler] async fn get_data(Path(id): Path(String)) -> Result<String, AppError> { let internal_context = format!(“DB Timeout on node 1: ID {}”, id); Err(AppError::DbFail(internal_context)) }
Your Poem API
might be exposed to Improper Error Handling
74% of Poem apps fail this check. Hackers use automated scanners to find this specific flaw. Check your codebase before they do.
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