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I've recently discovered a backdoor shell that was created via file injection on a public facing website. After much digging, I found the creation date of this file to be around the same time pentesting was done by others in the department. Most of this was done by persons not completely experienced with pentesting, and I wondered if one of the tools used injected the file, since in addition to the creation date, no evidence of its use surfaced. I myself will (almost) always do pentesting on a testing instance, vs live, so typically this isn't an issue, but will some of the various software available inject an actual file that creates a backdoor shell, or are the files that are injected "dummies"?

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What tool? What file? –  Terry Chia Nov 25 '13 at 11:38
    
Without saying what tools you used there's not a chance that you'll get a decent answer. Even if you do tell us, there are so many tools out there, and so many variants of them, that you may well still not have an answer Suffice to say it's pretty bad practice to not know what the tools you use are doing, so whoever did this pentest needs some guidance. –  Owen Nov 25 '13 at 17:22

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It is quite difficult to tell from the details you have provided. Typically if we had known what sort of software they used for their pentest, we could draw a more educated guess.

I have seen many pentest reports from different companies that were too focused on the technical findings, but very little, almost to nothing, about their methodologies. Having their methodologies clearly scoped and defined is vitally important for the pentest company and for the client both: it's the company's way of covering their own butt for when situations where potential collateral damage occur, and the client's guarantee that if the company side-tracks and, say, bring the company's site down due to a DoS that was not in scope, they can made liable for it.

Because a) pentesters are (or should) be perfectly capable of writing their own tools, and b) because the damage is already done (having a foreign file on your server is never good, whether is a genuine backdoor or a dummy file) your question,

[...] will some of the various software available inject an actual file that creates a backdoor shell, or are the files that are injected "dummies"?

... at this point becomes irrelevant: you have bigger problems at hand here such as 1) determining whether the tool was uploaded by the testers; and 2) the maturing of your pentesting process as a whole. Depending on the findings of 1), other investigations might beg some further attention: what if they claim that the shell was not their tool?

So the key point here is communication. If you are the analyst that facilitated the pentest, or the service owner, nothing will stop you from getting a full report from the testers on their methodology. Feel free to request a meeting to go through their methodology, as this will help you ascertain whether the 'forgotten' shell was a product of their negligence, or not - remember, always assume the worst and at this stage, there is nothing that guarantees that the shell was not a result of a true breach, either prior- or post-pentest.

For future pentests, in order to avoid this situation, make sure that:

  1. you have a clear internal process that deals with different situations that can arise from a failed pentest
  2. read their Proposal/Statement of Work and don't accept everything they throw over there; demand methodical description of their methodologies. Have clauses that address very clearly who is liable for what
  3. Know your assets

TL;DR - Summary

It is not possible for me to answer whether the security tools used in your pentest injected actual backdoors or dummy files, because the level of detail you have provided is not enough. Still, even if it were possible, at the current time, this is the least relevant question, and the recommendation is that you confront the pentesters for a thorough clarification.

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It was a file similar to c99shell. It was a full-featured php backdoor shell. The possible tool-set might have included metasploit, nessus, but definitely hailstorm. I myself don't run these types of tests on a public facing site, and the files have been removed, I'm also migrating the site to a more modern, update cms. However I'm wondering since the date of some of the records I know were created by pentesting tools coincided with this files creation date, if it wasn't an actual attack. –  tuson Nov 26 '13 at 4:56
    
@tuson - That makes sense. So the big question seems to be whether you have had a breach or the file was placed by the testers. No doubt for me, I would firstly speak with the testers and get this straight. If they say they definitely did not put/use/see the file, then the company will most certainly have to raise a security incident on a need-to-know basis. –  Lex Nov 26 '13 at 8:06
    
I've been trying to do some inquiring, but my last question I asked the IT department seemed to have been interpreted as an accusation, and I'm getting the feeling the person at the wheel just "hailmary"ed everything, without any actual analysis. The only info I have is what was left on the target. Thanks Everyone for taking the time to answer my question. –  tuson Nov 26 '13 at 13:19
    
@tuson You are welcome. I guess that's when social skills supersede technical skills; the deal is to make it look like you are there to help them avoid the worst in future. When people that have years experience in service delivery, and someone with less experience in that particular subject, but well versed in security comes along, that does tend to cause make their ego very sensitive. Just be friendly and reassure them of those main things: 1) explain why it is important to know if the file was theirs or a genuine breach; and 2) make them feel that you are not there to jeopardize their jobs. –  Lex Nov 26 '13 at 13:31
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And resist the urge to compare them to Dee Dee "ooooh! What does this button do?" :) –  tuson Nov 26 '13 at 13:34

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