CUPS: Multiple vulnerabilities

Background

CUPS provides a portable printing layer for UNIX-based operating systems. The alternate pdftops filter is a CUPS filter used to convert PDF files to the Postscript format via Poppler; the filter is installed by default in Gentoo Linux.

Description

Wei Wang (McAfee AVERT Research) discovered an integer underflow in the asn1_get_string() function of the SNMP backend, leading to a stack-based buffer overflow when handling SNMP responses (CVE-2007-5849). Elias Pipping (Gentoo) discovered that the alternate pdftops filter creates temporary files with predictable file names when reading from standard input (CVE-2007-6358). Furthermore, the resolution of a Denial of Service vulnerability covered in GLSA 200703-28 introduced another Denial of Service vulnerability within SSL handling (CVE-2007-4045).

Impact

A remote attacker on the local network could exploit the first vulnerability to execute arbitrary code with elevated privileges by sending specially crafted SNMP messages as a response to an SNMP broadcast request. A local attacker could exploit the second vulnerability to overwrite arbitrary files with the privileges of the user running the CUPS spooler (usually lp) by using symlink attacks. A remote attacker could cause a Denial of Service condition via the third vulnerability when SSL is enabled in CUPS.

Workaround

To disable SNMP support in CUPS, you have have to manually delete the file “/usr/libexec/cups/backend/snmp”. Please note that the file is reinstalled if you merge CUPS again later. To disable the pdftops filter, delete all lines referencing “pdftops” in CUPS’ “mime.convs” configuration file. To work around the third vulnerability, disable SSL support via the corresponding USE flag.

Resolution

All CUPS users should upgrade to the latest version:

 # emerge --sync
 # emerge --ask --oneshot --verbose ">=net-print/cups-1.2.12-r4"