Format String in Actix with Cockroachdb

A format string vulnerability occurs when user-controlled input is directly used as a format argument in functions like format! or write! without explicit format specification. In an Actix web service that interacts with CockroachDB, this typically arises when constructing SQL strings or log messages using unchecked user input. For example, concatenating a request parameter directly into a SQL string and then passing it to a formatting routine can expose the application to injection or information disclosure, because format specifiers such as %s, %x, or %n may interpret the input as format commands rather than literal data.

When using CockroachDB with Actix, developers often build queries using string formatting to insert dynamic values. If a developer writes format!("SELECT * FROM accounts WHERE id = {}", user_id) and user_id contains format-like content, the formatting operation may misinterpret parts of the input as format directives. This can lead to unexpected behavior, including panics or, in broader contexts, injection vectors when the resulting string is passed to a database driver. The risk is compounded when the formatted string is used in logging or error reporting, potentially leaking sensitive data through verbose error messages that include interpreted format tokens.

In a black-box scan, middleBrick checks for indicators of improper formatting by analyzing endpoint behavior with varied inputs that include format specifiers. For CockroachDB integrations in Actix, this includes detecting patterns where SQL strings are constructed using unchecked user input and then formatted or logged. The scanner evaluates whether the application sanitizes or parameterizes inputs before they are embedded into queries or diagnostic output, flagging cases where format operations depend on external data without strict validation or explicit format control.

Even when the immediate database query uses prepared statements, intermediate formatting steps—such as building identifiers or debug output—can still introduce risk if they rely on unchecked string interpolation. middleBrick’s checks for Data Exposure and Input Validation highlight these scenarios, ensuring that format-related issues are surfaced alongside other findings. By correlating runtime behavior with OpenAPI specifications, the scan can identify endpoints where formatting logic might expose sensitive information or create inconsistent query structures when interacting with CockroachDB.

To prevent format string issues when using CockroachDB with Actix, always use parameterized queries and avoid constructing SQL strings through formatting. Instead of interpolating values into SQL, rely on placeholders supported by the CockroachDB driver. This ensures that user input is treated strictly as data and never as executable code or format directives.

use actix_web::{web, HttpResponse};
use cockroachdb_rs::Client;

async fn get_account(
    pool: web::Data,
    path: web::Path<(i32,)>,
) -> HttpResponse {
    let id = path.0;
    // Safe: parameterized query with explicit placeholder
    match pool
        .query_opt("SELECT name, email FROM accounts WHERE id = $1", &[&id])
        .await
    {
        Ok(Some(row)) => {
            let name: String = row.get(0);
            let email: String = row.get(1);
            HttpResponse::Ok().json(json!({ "name": name, "email": email }))
        }
        Ok(None) => HttpResponse::NotFound().body("Not found"),
        Err(e) => {
            // Safe: logging with explicit format, no user input as format string
            tracing::error!(target: "db", error = %e, "Query failed");
            HttpResponse::InternalServerError().finish()
        }
    }
}

Ensure that any dynamic identifiers or table names—which cannot be parameterized—are validated against a strict allowlist before use. Never pass user input directly into format strings that build SQL or log messages. Use format! only with hardcoded templates and explicit format specifiers, and keep user data separate as arguments rather than embedding it in the format string itself.

For logging, prefer structured logging with typed fields so that sensitive data is not inadvertently interpolated. middleBrick’s Input Validation and Data Exposure checks validate that formatted outputs do not contain raw user input, helping to confirm that remediation aligns with secure coding practices for Actix and CockroachDB integrations.