Mozilla Foundation Security Advisory 2013-83

Mozilla Updater does not lock MAR file after signature verification

September 17, 2013
Seb Patane
Firefox, Firefox ESR, SeaMonkey, Thunderbird, Thunderbird ESR
Fixed in
  • Firefox 24
  • Firefox ESR 17.0.9
  • SeaMonkey 2.21
  • Thunderbird 24
  • Thunderbird ESR 17.0.9


Security researcher Seb Patane reported that the Mozilla Updater does not write-lock the MAR update file when it is in use by the Updater. This leaves open the possibility of altering the contents of the MAR file after the signature on the file has been verified as valid but before it has been used. This could allow an attacker with access to the local system to silently replace the contents of the update MAR file and either replace the installed software with their own or extract and run executables files with the same privileges as that of the Mozilla Updater.