[Development] New Qt vulnerabilities

Olivier Goffart olivier at woboq.com
Thu Jan 30 18:09:47 CET 2020

On 30/01/20 17:12, Thiago Macieira wrote:
> On Thursday, 30 January 2020 03:05:50 PST Olivier Goffart wrote:
>> $PWD is not the same as the binary dir
>> (QCoreApplication::applicationDirPath) The later is still searched while
>> looking for plugin. (so that covers the case where plugin is in the folder
>> next to the binary)
>> But I am also not sure why Windows is not affected.
> Because LoadLibrary() works differently from dlopen().
> The Qt plugin loader code will open the DLL relative to $PWD and inspect its
> plugin metadata, in order to decide whether to load or not. Then it tells
> LoadLibrary to load a plain filename with no path components and LoadLibrary()
> goes and searches the system paths (which include the .exe's) first. So it
> loads a different file.
> This is similar to a TOCTOU attack, but I couldn't come up with a reasonable
> attack scenario. If the interposing DLL has metadata saying not to load,
> QLibrary will find the actual plugin later and will load that. The worst that
> could happen is that the interposing DLL has valid but incorrect metadata
> causing another DLL to be loaded that shouldn't be. This other DLL isn't under
> the control of the attacker, though and neither is the name of the DLL.

I think a reasonable attack scenario remains if the plugin does not exist in 
the system.


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