Publique! Framework 2.3 SQL Injection

`=====[ Tempest Security Intelligence - Advisory #01 / 2010 ]=============  
  
  
  
SQL injection vulnerability in Publique! Framework  
--------------------------------------------------  
  
Authors:  
Christophe de la Fuente <christophe *SPAM* tempest.com.br>  
Gustavo Pimentel Bittencourt <gustavo.pimentel *SPAM* tempest.com.br>  
  
  
=====[ Table of Contents ]=================================  
  
1. Overview  
2. Detailed description  
3. Additional context & Solutions  
4. References  
5. Thanks  
  
  
=====[ Overview ]======================================  
  
  
* System affected: Publique! version 2.3 (Other versions may be vulnerable)  
* Release date: 25 January 2010  
* Impact: Successful exploitation of this vulnerability may lead to remote  
server compromise due the ability to recover administrative  
credentials of Publique! management interface.  
  
  
Publique! is a Content Management System (CMS) for Web applications by Fábrica  
Digital [1]. This framework claims to be designed for non-computer specialists,  
enabling them to update web site content directly from the internet.  
  
This product is largely used in Brazil by companies from various areas such as  
universities, government organizations, banks and independent product  
vendors [2].  
  
A remotely exploitable vulnerability was found in the framework core component.  
Exploitation of this bug does not require authentication and will lead to  
remotely exposed potentially sensitive information from the Publique! database.  
Particularly, an attacker can extract usernames and passwords needed to  
authenticate to the administrative interface and gain full control of the web  
site and (depending on certain conditions) the server itself.  
  
  
=====[ Detailed description ]================================  
  
Publique! references each page with a specific ID ("sid") that the framework  
uses in most of URLs. For instance, to access the page referred by ID=1, the  
following URL is used:  
  
http://your_website.com/publique/cgi/cgilua.exe/sys/start.htm?sid=1  
  
It was found that Publique! does not validate properly the "sid" parameter  
value and causes this input to be interpreted as a SQL command instead of  
ordinary data.  
  
The following error is displayed when a simple quote is added after the  
original value (sid=1'):  
  
------------------------------------------------------------------------------  
  
Content-type: text/html  
CGILua message  
Lua error on configuration (or extension)  
  
Error: unexpected type to index table  
Active Stack:  
function _ERRORMESSAGE at C code  
function _initStart at //S/Publique/work/carregal/sys/reader/start.lua  
main of //S/Publique/work/carregal/sys/reader/start.lua  
function old_dofile at C code  
function dofile at  
//S/Publique/work/carregal/cgi/cgilua/cgilua.conf/pos_env.lua  
main of string " write("") dofile(ReaderDir.."start.bin")  
write("\n") det", 2  
function dostring at C code  
function: 0042E0D0 at  
//S/Publique/work/carregal/cgi/cgilua/cgilua.conf/preprocess.lua  
function: 0042A8C8 at  
//S/Publique/work/carregal/cgi/cgilua/cgilua.conf/preprocess.lua  
function: 0035CE60 at  
//S/Publique/work/carregal/cgi/cgilua/cgilua.conf/cgilua.lua  
function: 0035D650 at  
//S/Publique/work/carregal/cgi/cgilua/cgilua.conf/cgilua.lua  
main of //S/Publique/work/carregal/cgi/cgilua/cgilua.conf/cgilua.lua  
  
CGILua 3.2.1 CGI ©1995-99.  
  
------------------------------------------------------------------------------  
  
After several tests, it appears that the framework is executing two SQL queries  
sequentially and the error is issued by the first query. It is unlikely that  
the bug could be exploited using conventional methods. However, it is possible  
to extract information from the database using Time-Based Blind SQL  
Injection [3].  
  
Basically, this consists of using some time-taking SQL operations (e.g.  
the BENCHMARK() MySQL built-in function) that will delay server responses if  
the specific condition is satisfied. By monitoring the response time, it is  
possible to know if the conditional expression is True or False.  
  
Using this technique, it is possible to extract the usernames and passwords  
needed to authenticate into the Publique! management interface. Database  
information can be retrieved by testing the ASCII value of each character  
returned by the injected query.  
  
For example, the following payload may be used to extract the ASCII value of  
the first character returned by the query:  
  
http://your_website.com/publique/cgi/cgilua.exe/sys/start.htm?sid=1))+UNION+ALL  
+SELECT+IF((ASCII(SUBSTRING((SELECT+CONCAT(F_Login,':',F_Password)+FROM  
+Publique.T_Actor+LIMIT+1+OFFSET+0),1,1))>97),BENCHMARK(1000000,MD5('A')),0)%23  
  
This query first concatenates "F_Login" and "F_Password" columns of the  
internal table "T_Actor" and returns the first row (thanks to the "LIMIT 1  
OFFSET 0" statement). Then, it checks if the ASCII value of the first character  
returned is greater than 97 (the letter 'a'). If the condition is satisfied it  
will trigger the BENCHMARK function, causing a significant delay in the server  
response (approximately 4 seconds using our test lab). By repeating the query  
with different values to compare to, it is possible to retrieve the exact value  
of the first character. The complete string can be extracted by reproducing the  
process for each character.  
  
Although the password is encrypted, it is possible to discover it. After  
further investigation and reverse engineering the Lua pre-compiled binaries of  
Publique! framework, it appears that the encryption algorithm used is  
reversible (i.e. is not a hashing function).  
  
Basically, before storing passwords in the database, the framework encrypts  
them with two CGILUA [4] built-in functions: "crypt()" [5] and "encode()" [6].  
Since the key used by the encryption algorithm is hard-coded in Publique!  
binaries, it is possible to retrieve the plain password from the cypher by  
using the two following built-in functions: "decrypt()" and "decode()".  
  
These plain credentials could be used to log into the Publique! management  
interface, enabling the framework upload functionality, and eventually  
permitting an attacker to install malicious code on the remote server, for  
example.  
  
  
=====[ Other contexts & Solutions ]============================  
  
As usual [7], we contacted the vendor. After 45 days waiting, Fábrica Digital  
did not provide us a public URL to a fix which addresses this problem to attach  
in this publication.  
  
  
=====[ Thanks ]========================================  
  
- Tempest Security Intelligence [8] - Tempest Pentest Team  
- Evandro Curvelo Hora <evandro *SPAM* tempest.com.br>  
  
  
=====[ References ]======================================  
  
[1] http://www.fabricadigital.com.br/  
[2] http://www.fabricadigital.com.br/publique/cgi/cgilua.exe/sys/start.htm?sid=34&UserActiveTemplate=fabrica2007  
[3] http://www.owasp.org/index.php/Blind_SQL_Injection  
[4] https://web.tecgraf.puc-rio.br/cgilua/index2.html  
[5] https://web.tecgraf.puc-rio.br/cgilua/secao5.html#crypt  
[6] https://web.tecgraf.puc-rio.br/cgilua/secao5.html#encode  
[7] http://www.cert.org/kb/vul_disclosure.html  
[8] http://www.tempest.com.br/  
  
  
===================================================  
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