A new libpng update has been released for Debian 6 LTS

Package : libpng
Version : 1.2.44-1+squeeze6
CVE ID : CVE-2012-3425 CVE-2015-8472 CVE-2015-8540

CVE-2015-8472
update incomplete patch for CVE-2015-8126

CVE-2015-8540
underflow read in png_check_keyword in pngwutil.c

CVE-2012-3425
The png_push_read_zTXt function in pngpread.c in libpng 1.0.x
before 1.0.58, 1.2.x before 1.2.48, 1.4.x before 1.4.10, and
1.5.x before 1.5.10 allows remote attackers to cause a denial
of service (out-of-bounds read) via a large avail_in field value
in a PNG image.