Tavis Ormandy discovered multiple vulnerabilites in Ghostscript, an interpreter for the PostScript language, which could result in denial of service, the creation of files or the execution of arbitrary code if a malformed Postscript file is processed (despite the dSAFER sandbox being enabled).
For the stable distribution (stretch), these problems have been fixed in version 9.20~dfsg-3.2+deb9u4.
We recommend that you upgrade your ghostscript packages.
Further information about Debian Security Advisories, how to apply these updates to your system and frequently asked questions can be found at: https://www.debian.org/security/