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Date: Tue, 15 Aug 2017 00:39:48 +0200
From: Jakub Wilk <jwilk@...lk.net>
To: oss-security@...ts.openwall.com
Subject: UnRAR: directory traversal + memory safety bugs

(I'm not sure UnRAR bugs are on-topic here. UnRAR is not free software, even 
though the source is available. But the last time UnRAR was discussed nobody 
objected, so hey, let me try too.)

I found directory traversal and a few memory safety bugs in UnRAR 5.5.6. These 
bugs have been fixed in UnRAR 5.5.7.

The memory safety bugs were found using American Fuzzy Lop.

Here are details of the bugs:

* Directory traversal

The PoC (traversal.rar) contains two symlinks and a regular file:

   cur -> .
   cur/par -> ..
   par/moo

This setup defeats UnRAR's directory traversal protections:

   $ ls ../moo
   /bin/ls: cannot access '../moo': No such file or directory

   $ unrar x traversal.rar
   ...
   Extracting  cur                                                       OK
   Extracting  cur/par                                                   OK
   Extracting  par/moo                                                   OK
   All OK

   $ ls ../moo
   ../moo

The code that was used to generate the PoC is available here:
https://github.com/jwilk/path-traversal-samples


* Out-of-bounds read in Archive::ReadHeader15 / EncodeFileName::Decode

The Archive::ReadHeader15 method contains the following code (with boring parts 
omitted):

   size_t NameSize=Raw.Get2();
   // ...
   char FileName[NM*4];
   size_t ReadNameSize=Min(NameSize,ASIZE(FileName)-1);
   Raw.GetB((byte *)FileName,ReadNameSize);
   FileName[ReadNameSize]=0;

   if (FileBlock)
   {
     if ((hd->Flags & LHD_UNICODE)!=0)
     {
       EncodeFileName NameCoder;
       size_t Length=strlen(FileName);
       Length++;
       NameCoder.Decode(FileName,(byte *)FileName+Length,
                        NameSize-Length,hd->FileName,
                        ASIZE(hd->FileName));
   // ...

If NameSize is bigger than NM*4, this can make EncodeFileName::Decode read past 
the bounds of the FileName array.

PoC: oob-archive-readheader15.rar


* Out-of-bounds reads in Unpack::Unpack20

This method contains:

     int DistNumber=DecodeNumber(Inp,&BlockTables.DD);
     unsigned int Distance=DDecode[DistNumber]+1;

The array size is 48; but for the PoC (oob-unpack-unpack20.rar), DistNumber is 
58.


* Buffer overflow in Unpack::LongLZ

This method contains:

   ChSetB[DistancePlace]=ChSetB[NewDistancePlace];

The array size is 256; but for the PoC (oob-unpack-longlz.rar), DistancePlace 
is 256.

-- 
Jakub Wilk

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