________________________________________________________________________ From the low-hanging-fruit-department ESET Generic Malformed Archive Bypass (BZ2 Checksum) ________________________________________________________________________ Release mode : Coordinated Disclosure Ref : [TZO-11-2020] - ESET Generic Malformed Archive Bypass (BZ2 Checksum) Vendor : ESET Status : Patched CVE : Unknown Dislosure Policy: https://caravelahq.com/b/policy/20949 Blog : https://blog.zoller.lu/p/tzo-11-2020-eset-generic-malformed.html Vendor Advisory : https://support.eset.com/en/modules-review-november-2019 Affected Products ================= All below version v. 1294 ESET Smart Security Premium ESET Internet Security ESET NOD32 Antivirus ESET Cyber Security Pro (MAC) ESET Cyber Security (MAC) ESET Mobile Security for Android ESET Smart TV Security ESET NOD32 Antivirus 4 for Linux Desktop I. Background ---------------------------- "For three decades we've been helping people to protect their digital worlds. From a small, dynamic company we've grown into a global brand with over 110 million users in 202 countries and territories. Many things have changed, but our core aspirations, philosophy and values remain the same – to help build a more secure digital world where everyone can truly Enjoy Safer Technology." II. Description ---------------------------- The parsing engine supports the ZIP archive format. The parsing engine can be bypassed by specifically manipulating an ZIP Archive Compression Information Field so that it can be accessed by an end-user but not the Anti-Virus software. The AV engine is unable to scan the container and gives 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 organisation 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 ---------------------------- Reported submissions were fixed in new version (v. 1296) of unpacker module Thanks to ESET for their customer focused approach to coordinating this vulnerability.