Greg Roelofs discovered and fixed several buffer overflows in pnmtopng which is also included in netpbm, a collection of graphic conversion utilities, that can lead to the execution of arbitrary code via a specially crafted PNM file.
For the oldstable distribution (woody) these problems have been fixed in version 9.20-8.5.
For the stable distribution (sarge) these problems have been fixed in version 10.0-8sarge2.
For the unstable distribution (sid) these problems will be fixed in version 10.0-11.
We recommend that you upgrade your netpbm package.