I am creating a Python Flask app that interfaces with an SQL database. One of the things it does is take user input and stores it in a database. My current way of doing it looks something like this
mycursor.execute(f"SELECT * FROM privileges_groups WHERE id = {PrivID}")
This is not a good or correct way of doing this. Not only can certain characters such as ' cause errors, it also leaves me susceptible to SQL injection. Could anyone inform me of a good way of doing this?
To protect against injection attacks you should use placeholders for values.
So change
mycursor.execute(f"SELECT * FROM privileges_groups WHERE id = {PrivID}")
to
mycursor.execute("SELECT * FROM privileges_groups WHERE id = ?", (PrivID,))
Placeholders can only store a value of the given type and not an arbitrary SQL fragment. This will help to guard against strange (and probably invalid) parameter values.
However, you can't use placeholders for table names and column names.
Note: trailing comma is required for one-element tuples only but not necessary for multiple-element tuples. The comma disambiguates a tuple from an expression surrounded by parentheses.
Related: How do parameterized queries help against SQL injection?
So, if you want to avoid a sql injection...you have to have a secure query i.e. you don't want your query to doing something it shouldn't be.
queryRun = "SELECT * FROM privileges_groups WHERE id = %s" % (PrivID)
When you use "%s" this variable as a placeholder, you avoid ambiguity as to what the injection can or cannot cause to the overall system.
then..run the .execute() call:
mycursor.execute(queryRun)
Note: this also can be done in one step having all the changes within the .execute() call but you maybe better off splitting into piece-wise approach.
This isn't 100 % but should help a lot.
Related
Pretty new to sqlite3, so bear with me here..
I'd like to have a function to which I can pass the table name, and the values to update.
I initially started with something like this:
def add_to_table(table_name, string):
cursor.execute('INSERT INTO {table} VALUES ({var})'
.format(
table=table_name,
var=string)
)
Which works A-OK, but further reading about sqlite3 suggested that this was a terribly insecure way to go about things. However, using their ? syntax, I'm unable to pass in a name to specify the variable.
I tried adding in a ? in place of the table, but that throws a syntax error.
cursor.execute('INSERT INTO ? VALUES (?)', ('mytable','"Jello, world!"'))
>> >sqlite3.OperationalError: near "?": syntax error
Can the table in an sql statement be passed in safely and dynamically?
Its not the dynamic string substitution per-se thats the problem. Its dynamic string substitution with an user-supplied string thats the big problem because that opens you to SQL-injection attacks. If you are absolutely 100% sure that the tablename is a safe string that you control then splicing it into the SQL query will be safe.
if some_condition():
table_name = 'TABLE_A'
else:
table_name = 'TABLE_B'
cursor.execute('INSERT INTO '+ table_name + 'VALUES (?)', values)
That said, using dynamic SQL like that is certainly a code smell so you should double check to see if you can find a simpler alternative without the dynamically generated SQL strings. Additionally, if you really want dynamic SQL then something like SQLAlchemy might be useful to guarantee that the SQL you generate is well formed.
Composing SQL statements using string manipulation is odd not only because of security implications, but also because strings are "dumb" objects. Using sqlalchemy core (you don't even need the ORM part) is almost like using strings, but each fragment will be a lot smarter and allow for easier composition. Take a look at the sqlalchemy wiki to get a notion of what I'm talking about.
For example, using sqlsoup your code would look like this:
db = SQLSoup('sqlite://yourdatabase')
table = getattr(db, tablename)
table.insert(fieldname='value', otherfield=123)
db.commit()
Another advantage: code is database independent - want to move to oracle? Change the connection string and you are done.
I'm having this function that communicates via pymysql to an SQL database stored to my localhost. I know there are similar posts about formatting an SQL section especially this one but could anyone suggest a solution?
Always getting TypeError: can't concat tuple to bytes. I suppose it's sth with the WHERE clause.
def likeMovement(pID):
print("Give a rating for the movement with #id:%s" %pID)
rate=input("Give from 0-5: ")
userID=str(1)
print(rate,type(rate))
print(pID,type(pID))
print(userID,type(userID))
cursor=con.cursor()
sqlquery='''UDPATE likesartmovement SET likesartmovement.rating=%s WHERE
likesartmovement.artisticID=? AND likesartmovement.userID=?''' % (rate,),
(pID,userID)
cursor.execute(sqlquery)
TypeError: not all arguments converted during string formatting
Thanks in advance!
The problem is that you're storing (pID,userID) as part of a tuple stored in sqlquery, instead of passing them as the arguments to execute:
sqlquery='''UDPATE likesartmovement SET likesartmovement.rating=%s WHERE
likesartmovement.artisticID=? AND likesartmovement.userID=?''' % (rate,)
cursor.execute(sqlquery, (pID,userID))
It may be clearer to see why these are different if you take a simpler example:
s = 'abc'
spam(s, 2)
s = 'abc', 2
spam(s)
Obviously those two don't do the same thing.
While we're at it:
You have to spell UPDATE right.
You usually want to use query parameters for SET clauses for exactly the same reasons you want to for WHERE clauses.
You don't need to include the table name in single-table operations, and you're not allowed to include the table name in SET clauses in single-table updates.
So:
sqlquery='''UDPATE likesartmovement SET rating=? WHERE
artisticID=? AND userID=?'''
cursor.execute(sqlquery, (rating, pID, userID))
I have wrote a query which has some string replacements. I am trying to update a url in a table but the url has % signs in which causes a tuple index out of range exception.
If I print the query and run in manually it works fine but through peewee causes an issue. How can I get round this? I'm guessing this is because the percentage signs?
query = """
update table
set url = '%s'
where id = 1
""" % 'www.example.com?colour=Black%26white'
db.execute_sql(query)
The code you are currently sharing is incredibly unsafe, probably for the same reason as is causing your bug. Please do not use it in production, or you will be hacked.
Generally: you practically never want to use normal string operations like %, +, or .format() to construct a SQL query. Rather, you should to use your SQL API/ORM's specific built-in methods for providing dynamic values for a query. In your case of SQLite in peewee, that looks like this:
query = """
update table
set url = ?
where id = 1
"""
values = ('www.example.com?colour=Black%26white',)
db.execute_sql(query, values)
The database engine will automatically take care of any special characters in your data, so you don't need to worry about them. If you ever find yourself encountering issues with special characters in your data, it is a very strong warning sign that some kind of security issue exists.
This is mentioned in the Security and SQL Injection section of peewee's docs.
Wtf are you doing? Peewee supports updates.
Table.update(url=new_url).where(Table.id == some_id).execute()
Pretty new to sqlite3, so bear with me here..
I'd like to have a function to which I can pass the table name, and the values to update.
I initially started with something like this:
def add_to_table(table_name, string):
cursor.execute('INSERT INTO {table} VALUES ({var})'
.format(
table=table_name,
var=string)
)
Which works A-OK, but further reading about sqlite3 suggested that this was a terribly insecure way to go about things. However, using their ? syntax, I'm unable to pass in a name to specify the variable.
I tried adding in a ? in place of the table, but that throws a syntax error.
cursor.execute('INSERT INTO ? VALUES (?)', ('mytable','"Jello, world!"'))
>> >sqlite3.OperationalError: near "?": syntax error
Can the table in an sql statement be passed in safely and dynamically?
Its not the dynamic string substitution per-se thats the problem. Its dynamic string substitution with an user-supplied string thats the big problem because that opens you to SQL-injection attacks. If you are absolutely 100% sure that the tablename is a safe string that you control then splicing it into the SQL query will be safe.
if some_condition():
table_name = 'TABLE_A'
else:
table_name = 'TABLE_B'
cursor.execute('INSERT INTO '+ table_name + 'VALUES (?)', values)
That said, using dynamic SQL like that is certainly a code smell so you should double check to see if you can find a simpler alternative without the dynamically generated SQL strings. Additionally, if you really want dynamic SQL then something like SQLAlchemy might be useful to guarantee that the SQL you generate is well formed.
Composing SQL statements using string manipulation is odd not only because of security implications, but also because strings are "dumb" objects. Using sqlalchemy core (you don't even need the ORM part) is almost like using strings, but each fragment will be a lot smarter and allow for easier composition. Take a look at the sqlalchemy wiki to get a notion of what I'm talking about.
For example, using sqlsoup your code would look like this:
db = SQLSoup('sqlite://yourdatabase')
table = getattr(db, tablename)
table.insert(fieldname='value', otherfield=123)
db.commit()
Another advantage: code is database independent - want to move to oracle? Change the connection string and you are done.
I am currently trying to use place holders in my PostgreSQL query within Python's psycopg's module. Here is a sample of the code I am using.
table.execute('SELECT * FROM table WHERE col2 = %s ORDER BY pID ASC LIMIT %s OFFSET %s;',(val1,val2,val3))
I read somewhere that it is not possible to use placeholders like this for LIMIT and OFFSET however I should use this placeholder format for WHERE =.
safely specifying 'order by' clause from user input in python / postgresql / psycopg2
Does anyone know the proper placeholder syntax for this sql query? Thanks!
Limit and offset can both be used with placeholders without any issue.
Generally speaking you can use placeholders wherever a 'value' would be allowed in an expression.
cur.execute("select * from node where node_name = %s limit %s offset %s", ('test', 5, 5))
Works just fine.
As already noted in the referenced article you cannot use placeholders to refer to tables, columns, schemas, or aliases for any of them. In those cases you generally need to do your own variable substitution before calling execute.
In very old versions of PostgreSQL, it was indeed not possible to use placeholders in LIMIT and OFFSET clauses. This functionality was added in version 7.4, so it is safe to assume that it exists in current installations.
But that only applies to server-side prepared statements. Psycopg does not use server-side prepared statements. It does its own string substitution and sends the resulting string to the backend as a constant. So in principle, you can use its parameter substitution feature anywhere there resulting literal would be syntactically valid.
So what you are proposing to do is fine either way.