[Bug 1055614] Re: captive web portal corrupt Indexes

[Paul F]

Still present in 12.04 LTS, Precise running apt 0.8.16

In my case the corrupted package list files in /var/lib/apt/lists are
caused by the router redirecting to an internal help page when it
realises that its internet connection is down. So, when a fetch is
attempted from, say gb.archive.ubuntu.com/ubuntu/dists/precise-
updates/universe/binary-i386/Packages when checking for updates what
comes back is the html source from the router's help page (example
attached -- line 52 contains the requested url).

It would appear that no sanity check is done on the returned data
leaving subsequent parse attempts to choke. The corrupted files remain
and may propagate (???) causing other update failures.

On a security note, it occurs to me that an attacker in control of the
router could return crafted files in place of apt's package lists to
introduce malware as part of the normal automated update process. I
trust checks are in place to prevent this???

** Attachment added: "Example corrupted package list file from /var/lib/apt/lists"
   https://bugs.launchpad.net/ubuntu/+source/update-manager/+bug/1055614/+attachment/3341892/+files/gb.archive.ubuntu.com_ubuntu_dists_precise-updates_universe_binary-i386_Packages.IndexDiff

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https://bugs.launchpad.net/bugs/1055614

Title:
  captive web portal corrupt Indexes

Status in “update-manager” package in Ubuntu:
  Confirmed

Bug description:
  When the computer is connected to a captive web portal, the update
  manager does not check to see that files downloaded are valid indexes.
  This results in the web portal's html file being written over some or
  all of the files in /var/lib/apt/lists.  I have been able to remove
  the corrupted files (assuming if they are that easy to overwrite, then
  blowing them away will be OK too) with the following command:

  cd /var/lib/apt/lists
  for foo in `grep -r weblogin.jsp .|cut -f 1 -d ':'`; do sudo rm -f $foo; done

  This is not something a new user could be expected to do.   I don't
  know if the behavior has changed recently, but this is the second time
  I have run into this bug in the last month.

  This results in complete breakage of the update system stops all
  updating until it is fixed.  The user does get a little red error icon
  with an relatively opaque error message which was how I knew to look
  in the /var/lib/apt/lists directory.

  This prevents all security updates so I have flagged it as a security
  vulnerability.

  1) The release of Ubuntu you are using, via 'lsb_release -rd' or System -> About Ubuntu
  bryan at bryan-Aspire-V3-771:~/temp$ lsb_release -rd
  Description:	Ubuntu 12.04.1 LTS
  Release:	12.04

  2) The version of the package you are using, via 'apt-cache policy pkgname' or by checking in Software Center
  bryan at bryan-Aspire-V3-771:~/temp$ apt-cache policy update-manager
  update-manager:
    Installed: 1:0.156.14.9
    Candidate: 1:0.156.14.9
    Version table:
   *** 1:0.156.14.9 0
          500 http://us.archive.ubuntu.com/ubuntu/ precise-updates/main amd64 Packages
          100 /var/lib/dpkg/status
       1:0.156.14.5 0
          500 http://security.ubuntu.com/ubuntu/ precise-security/main amd64 Packages
       1:0.156.14 0
          500 http://us.archive.ubuntu.com/ubuntu/ precise/main amd64 Packages

  3) What you expected to happen
  /var/lib/apt/lists should not get corrupted when the computer is on a captive portal before login.  

  4) What happened instead
  /var/lib/apt/lists does get corrupted in a way that has no (obvious to a normal user) fix.

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