full-disclosure - gnu-less Format String Vulnerability

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From: sakpolat at gmx.net (Serkan Akpolat)
Subject: gnu-less Format String Vulnerability

Tim wrote:
>>+-----[ Description ]-----+
>>
>>Format string vulnerability.
>>
>>
>>+-----[ Vulnerable Code ]-----+
>>From less-382:
>>
>>[filename.c] : 787
>>
>>    public char *
>>open_altfile(filename, pf, pfd)
>>    char *filename;
>>    int *pf;
>>    void **pfd;
>>{
>>    ...................
>>    if ((lessopen = lgetenv("LESSOPEN")) == NULL
>>    ...................
>>    sprintf(cmd, lessopen, filename); <-- Format String Problem Here
>>    ...................
>>
>>}
> 
> 
> 
> I am sorry, I fail to see how this is a vulnerability.
> 
> If you have control of LESSOPEN, you already have shell, since, from the
> man page:
> 
> "An input preprocessor is simply an executable program (or shell
> script), which writes the  contents of the file to a different file,
> called the replacement file.
> ...
> To  set  up  an input  preprocessor, set the LESSOPEN environment
> variable to a command line which will invoke your  input  preprocessor."
> 
> 
> Perhaps it would be better written if the LESSOPEN parser only allowed
> %s to work, as advertized, and not the other sprintf codes, but it
> really isn't a security issue (unless I am totally missing something).
> If you are really worried about it, add the -L option when running less,
> and it will ignore LESSOPEN.
> 
> cheers,
> tim
> 

Yes , thank you for correction.
It is a bug not a vulnerability.