Release mode : Forced Disclosure
Ref : [TZO-04-2019] - Bitdefender Malformed Archive bypass (BZ2)
Vendor : Bitdefender
Status : Patched (amsiscan.dll >24.0.14.74)
CVE : Issued 3 CVEs then pulled them back (although patching the vuln)
Dislosure Policy: https://caravelahq.com/b/policy/20949
Blog : https://blog.zoller.lu
Vendor Advisory : No Advisory issued
Patch release : https://www.bitdefender.com/consumer/support/answer/10690/
References
[1] More information and details about this bug class: https://blog.zoller.lu/2009/04/case-for-av-bypassesevasions.html
[2] Our presentation at Hack.lu and CansecWest entitled "The Death of AV Defence in Depth?"
[3] It didn't go unnoticed - Past Press Coverage: Washington Post, Infoworld, Heise, Security Focus ... etc.[4] https://www.bleepingcomputer.com/news/security/specially-crafted-zip-files-used-to-bypass-secure-email-gateways/ | https://www.techradar.com/news/zip-files-are-being-used-to-bypass-security-gateways
Affected Products
All Bitdefender Products and Vendors that have licensed the Engine before Dec 12 2019. Exact version is unknown as Bitdefender has not made this public.
Quoting Bitdefender :
"All Bitdefender endpoint solutions (including but not limited to Bitdefender Total Security,
Bitdefender Antivirus Free Edition, Bitdefender GravityZone) as well as all products
using our engines."
Consumer:
Bitdefender Premium Security
Bitdefender Total Security 2020
Bitdefender Internet Security 2020
Bitdefender Antivirus Plus 2020
Bitdefender Family Pack 2020
Bitdefender Antivirus for Mac
Bitdefender Mobile Security for Android
Bitdefender Mobile Security for iOS
Enterprise:
Bitdefender Small Office Security
GravityZone Business Security
GravityZone Advanced Business Security
Bitdefender Security for AWS
GravityZone Ultra Security
GravityZone Managed EDR
GravityZone Elite Security
GravityZone Enterprise Security
Security for Virtualized Environments
Security for Endpoints
Security for Mobiles
Security for Exchange
GravityZone Security for Storage
Vulnerable OEM Partners (According to AV-TEST):
Adaware
Bullguard
Vipr
Total360
eScan
emiSoft
G-DATA
Qihoo 360
Quick Heal
TotalDefense
Tencent
I. Background
"Since 2001, Bitdefender innovation has consistently delivered award-winning security products and threat intelligence for people, homes, businesses and their devices, networks and cloud services. Today, Bitdefender is also the provider of choice, used in over 38% of the world’s security solutions.
Recognized by industry, respected by vendors and evangelized by our customers, Bitdefender is the cybersecurity company you can trust and rely on."
II. Description
The parsing engine supports the BZIP archive format. The parsing engine can be bypassed by specifically manipulating a BZIP Archive so that it can be accessed by an end-user but not the Anti-Virus software. The AV engine is unable to scan the archive and issues the file a "clean" rating.
I may release further details after all known vulnerable vendors have patched their products.
III. Impact
Impacts depends on the contextual use of the product and engine within the organization of a customer. Gateway Products (Email, HTTP Proxy etc) may allow the file through unscanned and give it a clean bill of health. Server-side AV software will not be able to discover any code or sample contained within this ISO file and it will not raise suspicion even if you know exactly what you are looking for (Which is, for example, great to hide your implants or Exfiltration/Pivot Server).
There is a lot more to be said about this bug class, so rather than bore you with it in this advisory I provide a link to my 2009 blog post
http://blog.zoller.lu/2009/04/case-for-av-bypassesevasions.html
IV. Patch / Advisory
If you are an enterprise customer I would suggest to reach out to Bitdefender to discuss how you can be notified about patched vulnerabilities within their products. Some releases may require binary updates that cant be pulled from the auto-update.
amsiscan.dll >24.0.14.74
Users of the OEM Partners (G-Data, Vipr, etc) I would suggest to get in contact to ensure these vulnerabilities are patched or not present in their offering. I would also suggest discussing how you can be made aware of future vulnerabilities.
V. Disclosure Timeline
See here: https://caravelahq.com/b/bitdefender/20876
18 OCT 2019
- Submission of a bypass over a bug bounty platform (that will remain unnamed) that requires submitters to agree to an NDA regardless if the vulnerability is recognized or not.
21 OCT 2019
- Bitdefender validated the report and assigned CVE-2019-17095
23 OCT 2019
"fix was also pushed via update. Can you please check?"
OCT 2019
- Back and forth on whether this qualifies for a bug bounty. Bitdefender rep states "In my opinion, we should. It's not an usual engine bypass "undetected sample". It's exploiting a vulnerability to bypass the engines which, I see as something different. Will provide an official answer in the following days."
- I continue submitting more Bitdefender bypasses
28 OCT 2019
- Bitdefender states "We're doing a review of this vector as a whole and putting the unpackers
temporarily out of scope until we're done"
05 NOV 2019
- Bitdefender changes its mind "As a rule of thumb, this form of AV bypass (corrupting archive headers)
is not and will not be rewardable."
Discussion continue
26 NOV 2019
"Your reports are valid but they will not be treated as vulnerabilities or receive a generic fix at the moment (individual fixes may be implemented)."
"PS: given that we won't be treating these as vulnerabilities, we're pulling back the 3 CVEs that may have been issued a bit too rashly."
Read: We qualified them as vulnerabilities and in scope of the bug bounty, now we changed our mind,
they are valid yes, i.e they bypass the Engine, but they are not vulnerabilities.
At this point the Terms I agreed to when signing up to the bug bounty platform would prevent me from disclosing or getting any sort of credit for my work and report. I decided to take my next report outside the platform and under my own terms that can be found here : https://caravelahq.com/b/policy/20949
OCT 30 2019
- Submitted new GZIP bypass report and sample over my ticketing system and under my terms,
outside of the bug bounty platform.
OCT 31 2019
- Bitdefender requests that I reupload the file as they accidentally deleted it
NOV 5 2019
- I continue to try to talk sense into this by sending a bunch of CVEs, reports, papers, and presentations about this bug class.
- I notify Bitdefender that "Also, I will stop reporting any further vulnerabilities to you under these conditions. I feel like you broke both contract and execution in good faith. When are you planning on notifying your customers?"
NOV 5 2019
Bitdefender : "While this may change in the future. we're treating these types of AV evasion techniques as "won't fix", for now."
NOV 14 2019
- Setting a temporary Disclosure data as per my Policy.
- Asking to confirm the vulnerability or otherwise reply - No reply.
NOV 21 2019
- Notifying Bitdefender that that in alignment to my policy, .i.e having received no updates that I will disclose without further coordination.
NOV 26 2019
- Bitdefender issues a bounty for previous reports over the previously used bug bounty platform.
DEC 2 2019
- Asking a second time for an update (Bz2). No reply.
DEC 6 2019
- The last attempt to contact them. Bz2) No reply.
DEC 12 2019
Bitdefender silently fixes the vulnerability -
"I noticed today the 12/12/2020 that you have deployed a fix for this. Do you have any statement or comment on why you choose to silently fix and give no credit whatsoever ?"
DEC 12 2019
- Tweeted the Hash of the Report
https://twitter.com/thierryzoller/status/1205115141832007680
DEC 13 2019
- Since I received no reply, I reached out to Bitdefender on an old thread on the previously used bug bounty platform.
"Have you considered not paying a bounty but giving credit?"
Bitdefender replies "This is literally the first time in 4 years of running the bug bounty program when we got "stuck" in a dispute of sorts with a researcher. I know what silent patching means and I'm fully aware (and against) this type of lack of transparency. And we also have a track record that shows we have absolutely no problem giving credit where credit was due. This is just a matter of you and us disagreeing on whether this is a vuln or not."
N.B They clearly classified it as a vulnerability weeks before, multiple times.
DEC 15 2019
- Reached out to Bitdefender again to ensure there is 0 excuse for "miscommunication"
"I'd like to make sure there are no misunderstandings if you recognize this bug class by either crediting or otherwise than I am happy to report any findings here, or outside. If you choose to continue to fix these silently and not even reply to my update requests I am not open in doing so. Let me know Bitdefenders' official position on this."
DEC 16 2019
- "You shall be credited in our hall of fame and I'll post about this on Twitter."
DEC 24 2019
- Release of this Advisory
Note: The length you need to go through in 2019 to report vulnerabilities is astounding, it is also astounding to see how bug bounty platforms have the potential to be used to silence reports and/or researchers. Their terms and usages introduce a new element and dynamic in the researcher/vendor relationship. Is it about time to push an FD culture again?
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