Skype Can't Fix a Nasty Security Bug Without a Massive Code Rewrite

'ZDNet reports of a security flaw in Skype's updater process that "can allow an attacker to gain system-level privileges to a vulnerable computer." If the bug is exploited, it "can escalate a local unprivileged user to the full 'system' level rights -- granting them access to every corner of the operating system." What's worse is that Microsoft, which owns Skype, won't fix the flaw because it would require the updater to go through "a large code revision." Instead, Microsoft is putting all its resources on building an altogether new client. From the report: Security researcher Stefan Kanthak found that the Skype update installer could be exploited with a DLL hijacking technique, which allows an attacker to trick an application into drawing malicious code instead of the correct library. An attacker can download a malicious DLL into a user-accessible temporary folder and rename it to an existing DLL that can be modified by an unprivileged user, like UXTheme.dll. The bug works because the malicious DLL is found first when the app searches for the DLL it needs. Once installed, Skype uses its own built-in updater to keep the software up to date. When that updater runs, it uses another executable file to run the update, which is vulnerable to the hijacking. The attack reads on the clunky side, but Kanthak told ZDNet in an email that the attack could be easily weaponized. He explained, providing two command line examples, how a script or malware could remotely transfer a malicious DLL into that temporary folder. ' -- source: https://it.slashdot.org/story/18/02/12/2319257 Cheers, Peter -- Peter Reutemann Dept. of Computer Science University of Waikato, NZ +64 (7) 858-5174 http://www.cms.waikato.ac.nz/~fracpete/ http://www.data-mining.co.nz/

On Tue, 13 Feb 2018 16:03:44 +1300, Peter Reutemann quoted:
'... Skype uses its own built-in updater to keep the software up to date. When that updater runs, it uses another executable file to run the update, which is vulnerable to the hijacking.'
Auto-updaters seem to be a frequent case of reinventing the wheel and getting it wrong. IBM suffers from the same problem <http://www.theregister.co.uk/2018/02/12/notes_dll_impersonation_bug/>. Wonder why Windows cannot have a Linux-style integrated package-management system that solves this problem once and for all? Because vendors of third-party proprietary software would see it as a violation of their “intellectual property”.

On Tue, 13 Feb 2018 16:03:44 +1300, Peter Reutemann quoted:
' Security researcher Stefan Kanthak found that the Skype update installer could be exploited with a DLL hijacking technique ...'
Microsoft is now saying it fixed that back in October <http://www.theregister.co.uk/2018/02/15/microsoft_skype_fixed/>.
participants (2)
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Lawrence D'Oliveiro
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Peter Reutemann