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Re: [CVE-2014-1860] PHP object insertion / possible RCE in Contao CMS <= 3.2.4
From: Egidio Romano <research () karmainsecurity com>
Date: Sat, 08 Feb 2014 14:30:45 +0100
Hello Mario, Rest assured, it wasn't my intention to get into a flame war! :) The thing is that I am one of that kind of people that is called "like San Tommaso" in Italy. In other words, I'm not able to believe in something until I can see it with my eyes. Well, now Stefan Esser has provided a PoC for CVE-2014-1860 [1], proving that I was wrong. Sadly, I'm just a human being, and as everybody knows, "errare humanum est". I just hope that now he is happy to have proven to be smarter than me. On the other hand, just because his PHP exploitation skills are better than mine, it doesn't necessarily mean he's smarter than me, especially considering the fact that he is part of the PHP development team. However, I never thought to be such a smart guy, and very likely he is actually smarter than me. So, it seems I need to apologize to Pedro Ribeiro: please accept my apologies for doubting about the validity of your report. Nevertheless, if we want to be picky, actually your report is only 33.3% true, since you reported two deserialize()s called with user input accessed via the Input::post method (which seems to be not vulnerable), and only one via the Input::postRaw method, that is what I missed, and this made me think it wasn't exploitable. Finally, I really would like to congratulate with Mr. Esser, since he claims [2] to be aware of this security hole for (who knows how many) years. However it seems he preferred to keep this as 0-day, instead of reporting to the Contao team and help to improve the security of an open source project. References: [1] http://pastebin.com/DFh1FVdb [2] http://oi59.tinypic.com/2rpwthj.jpg Have a great weekend! /Egidio On 07/02/2014 11:46, Mario Vilas wrote:
I haven't read the whole thread, so I apologize in advance for commenting on it. But I think it's important to mention that "not a vulnerability" and "not exploitable" are entirely different concepts. Since conclusively proving that a vulnerability is 100% not exploitable for all code paths in all possible environments is difficult at best (if not downright impossible), you can still consider something a vulnerability even if you don't have a proof of concept - you can assign it lower risk, of course, but it doesn't disappear, because there's at least a theoretical possibility that it may be exploited. So, let's not get into a flame war yet. :) On Fri, Feb 7, 2014 at 12:15 AM, Egidio Romano wrote: Hello again, today a little bird known as "i0n1c" twitted something about me [1], claiming that I was wrong, and that CVE-2014-1860 could actually be exploited, "because there is S: which allows encoded NUL bytes" [2], and that's true in part. So, instead of using a string like this: O:9:"ZipWriter":1:{s:10:"\0*\0strTemp";s:11:"/etc/passwd";} An attacker might be able to bypass the filter implemented within the Input::xssClean() method because she can also use a string like this: O:9:"ZipWriter":1:{S:10:"\00*\00strTemp";s:11:"/etc/passwd";} The Input::xssClean() method removes not only NULL bytes, but also the string "\0", meaning that the above string will be converted to: O:9:"ZipWriter":1:{S:10:"0*0strTemp";s:11:"/etc/passwd";} Of course this could easily be bypassed using a string like this: O:9:"ZipWriter":1:{S:10:"\\000*\\000strTemp";s:11:"/etc/passwd";} However, in such case there's another filter which doesn't allow to inject *protected* or *private* objects' properties, and that is implemented within the Input::encodeSpecialChars() method [3], which converts backslashes into "\", meaning that the above string will be converted to: O:9:"ZipWriter":1:{S:10:"\00*\00strTemp";s:11:"/etc/passwd";} Therefore, unless somebody (like Pedro Ribeiro or Mr. Stefan Esser) provides a working Proof of Concept, I will continue to believe that CVE-2014-1860 should be rejected as non-vulnerability. References: [1] https://twitter.com/i0n1c/status/431367715941400576 [2] https://twitter.com/i0n1c/status/431368722624704512 [3] http://git.io/DFkxDQ Kind Regards, Egidio Romano > > On Wed, Feb 05, 2014 at 11:13:29PM +0100, Egidio Romano wrote: > Hello, > > I believe this CVE should be rejected, because the vulnerabilities > actually don't exist, at least the ones mentioned in this report. > > The reason is that user input is passed to the unserialize() function > through the Contao Input class, in which the Input::xssClean() method > removes all the NULL bytes from user input, meaning that an attacker can > be able to manipulate only the *public* properties of the injected > objects, because *protected* and *private* properties of a serialized > object are encoded with NULL bytes. > > I haven't found any exploitable magic method in Contao which uses only > *public* properties, and the ones mentioned in the original report are > exploitable only through *protected* properties. > > Therefore, unless someone provides a working Proof of Concept, I think > these shouldn't be considered actual security vulnerabilities. > > Best Ragards, > Egidio Romano > >> >> Hi, >> >> I have discovered a vulnerability that might lead to code execution in >> Contao CMS <= 3.2.4 >> Contao CMS <= 3.2.4 does not properly validate user input in several >> locations which is then passed directly into PHP's unserialize. >> >> This has been fixed in Contao 3.2.5 as per commit: >> https://github.com/contao/core/commit/8c9cb044bdc887a8202bb65a64545c025664f957 >> and >> https://github.com/contao/core/commit/1717336598fdcf1ed3f4ad488e140147cb31516d >> >> Announcements can be found at >> >> https://contao.org/en/news/contao-3_2_5.html >> >> https://contao.org/en/news/contao-2_11_14.html >> >> Thanks to the Contao developers for being so responsive. >> The full report can be found at my repo in >> https://github.com/pedrib/PoC/blob/master/contao-3.2.4.txt >> >> Regards, >> >> Pedro Ribeiro >> Agile Information Security >>
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Current thread:
- [CVE-2014-1860] PHP object insertion / possible RCE in Contao CMS <= 3.2.4 Pedro Ribeiro (Feb 04)
- Re: [CVE-2014-1860] PHP object insertion / possible RCE in Contao CMS <= 3.2.4 Egidio Romano (Feb 06)
- Re: [CVE-2014-1860] PHP object insertion / possible RCE in Contao CMS <= 3.2.4 Egidio Romano (Feb 07)
- Re: [CVE-2014-1860] PHP object insertion / possible RCE in Contao CMS <= 3.2.4 Mario Vilas (Feb 07)
- Re: [CVE-2014-1860] PHP object insertion / possible RCE in Contao CMS <= 3.2.4 Egidio Romano (Feb 09)
- Re: [CVE-2014-1860] PHP object insertion / possible RCE in Contao CMS <= 3.2.4 Egidio Romano (Feb 07)
- Re: [CVE-2014-1860] PHP object insertion / possible RCE in Contao CMS <= 3.2.4 Egidio Romano (Feb 06)