add sql-direct writeup

picoctf/web/sql-direct/sql-direct-writeup.md

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+# sql-direct
+
+## Summary
+
+This challenge requires connecting directly to a PostgreSQL database server and using basic SQL syntax to discover and query a table containing the flag. No exploitation is needed, but the goal is to enumerate the database schema and retrieve the flag using SQL commands.
+
+**Artifacts:**
+- Remote PostgreSQL instance at `saturn.picoctf.net:55688`
+
+---
+
+## Context
+
+The challenge provides a hostname, port, username (`postgres`), and password (`postgres`) to connect to a live PostgreSQL database named `pico`. PostgreSQL (also called Postgres) is an open-source relational database management system. Data is organized into **databases**, which contain **tables** comprised of **columns** and **rows**.
+
+`psql` is the official commandline interface for interacting with PostgreSQL. It allows you to run SQL queries and psql meta-commands (prefixed with `\`) directly from the terminal.
+
+---
+
+## Vulnerability
+
+ In this challenge, the database is intentionally exposed with public credentials, and the flag is stored in plaintext inside a table. The vulnerability is simply unauthenticated (or publicly credentialed) access to a database containing sensitive data.
+
+---
+
+## Exploitation
+
+### Step 1 — Connect to the database
+
+Using `psql` with the provided credentials:
+
+```
+$ psql -h saturn.picoctf.net -p 55688 -U postgres pico
+Password for user postgres:
+psql (18.3 (Homebrew), server 15.2 (Debian 15.2-1.pgdg110+1))
+Type "help" for help.
+
+pico=#
+```
+
+The `pico` argument specifies the database name. After entering the password `postgres`, we are dropped into an interactive psql session.
+
+### Step 2 — Explore available psql commands
+
+I ran `help` to show the available meta-commands:
+
+```
+pico=# help
+Type:  \copyright for distribution terms
+       \h for help with SQL commands
+       \? for help with psql commands
+       \g or terminate with semicolon to execute query
+       \q to quit
+```
+
+Notably, `\?` lists all psql meta-commands. Among them:
+
+```
+\d[S+] NAME    describe table, view, sequence, or index
+```
+
+Running `\d` with no argument lists all relations (tables, views, etc.) in the current database.
+
+### Step 3 — Enumerate the database schema
+
+```
+pico=# \d
+         List of relations
+ Schema | Name  | Type  |  Owner
+--------+-------+-------+----------
+ public | flags | table | postgres
+(1 row)
+```
+
+There is one table: `flags`, owned by `postgres` in the `public` schema. This pointed to the next obvious course of action in uncovering the flag.
+
+### Step 4 — Dump the table contents
+
+I then used a `SELECT *` query to retrieve all rows and columns from the `flags` table:
+
+```
+pico=# select * from flags;
+ id | firstname | lastname  |                address
+----+-----------+-----------+----------------------------------------
+  1 | Luke      | Skywalker | picoCTF{L3arN_S0m3_5qL_t0d4Y_31fd14c0}
+  2 | Leia      | Organa    | Alderaan
+  3 | Han       | Solo      | Corellia
+(3 rows)
+```
+
+The flag is stored in the `address` column of the first row.
+
+**Flag:** `picoCTF{L3arN_S0m3_5qL_t0d4Y_31fd14c0}`
+
+---
+
+## Exploit Primitives Used
+
+- Direct connection to an exposed PostgreSQL instance using `psql`
+- Database schema enumeration with `\d`
+- Full table dump with `SELECT * FROM flags;`
+
+---
+
+## Remediation
+
+To prevent unauthorized access to sensitive data stored in a database:
+
+- **Do not expose database ports publicly.** The PostgreSQL port should be firewalled and only be accessible from trusted internal services.
+- **Use strong, unique credentials.** Default credentials like `postgres/postgres` should not be used in any environment.
+- **Apply least-privilege access controls.** Database users should only have access to the specific tables and operations they need.
+- **Encrypt sensitive data at rest.** Storing flags or other sensitive values in plaintext columns means anyone with read access can retrieve them immediately.
+
+## References
+
+https://play.picoctf.org/practice/challenge/303?category=1&page=3
+https://www.postgresql.org/docs/current/app-psql.html
+https://www.postgresql.org/docs/current/information-schema.html
+
+Written by Tatyana Ilieva