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Vulnerability of ISC DHCP: denials of service

Synthesis of the vulnerability 

An attacker can send two malicious packets to an ISC DHCP server, in order to stop it.
Vulnerable software: Debian, Fedora, ISC DHCP, Mandriva Linux, openSUSE, RHEL, SUSE Linux Enterprise Desktop, SLES.
Severity of this announce: 2/4.
Number of vulnerabilities in this bulletin: 2.
Creation date: 11/08/2011.
Références of this computer vulnerability: BID-49120, CERTA-2011-AVI-452, CERTA-2011-AVI-493, CVE-2011-2748, CVE-2011-2749, DSA-2292-1, FEDORA-2011-10705, FEDORA-2011-10740, MDVSA-2011:128, openSUSE-SU-2011:1021-1, RHSA-2011:1160-01, SUSE-SU-2011:1023-1, SUSE-SU-2011:1023-2, VIGILANCE-VUL-10915.

Description of the vulnerability 

The BOOTP and DHCP protocols use compatible packet formats:
 - 40 bytes: common headers
 - sname (64 bytes): server name
 - file (128 bytes): boot file name
 - options (variable size): options (named "vendor-specific area" in the RFC 951 of BOOTP, and limited to 64 bytes for BOOTP)
However, the ISC DHCP server does not correctly process the size of these fields.

When a DHCP/BOOTP packet does not contain the sname/file fields, the got_one() function of the common/discover.c file tries to access them, so a memory read error occurs. [severity:2/4]

The cons_options() function of the common/options.c file does not correctly compute the size of the "vendor-specific area" field of BOOTP when it has to be truncated to 64 bytes. The ack_lease() function of the server/dhcp.c file does not check if the pointer to options is NULL, before dereferencing it. [severity:2/4]

An attacker can therefore send two malicious packets to an ISC DHCP server, in order to stop it.
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This computer weakness alert impacts software or systems such as Debian, Fedora, ISC DHCP, Mandriva Linux, openSUSE, RHEL, SUSE Linux Enterprise Desktop, SLES.

Our Vigil@nce team determined that the severity of this weakness note is medium.

The trust level is of type confirmed by the editor, with an origin of LAN.

This bulletin is about 2 vulnerabilities.

An attacker with a expert ability can exploit this weakness bulletin.

Solutions for this threat 

ISC DHCP: versions 3.1-ESV-R3, 4.1-ESV-R3 and 4.2.2.
Versions 3.1-ESV-R3, 4.1-ESV-R3 and 4.2.2 are corrected:
  https://www.isc.org/downloads/all

Debian: new isc-dhcp packages.
New packages are available:
  isc-dhcp 3.1.1-6+lenny6
  isc-dhcp 4.1.1-P1-15+squeeze3

Fedora: new dhcp packages.
New packages are available:
  dhcp-4.2.0-23.P2.fc14
  dhcp-4.2.1-10.P1.fc15

Mandriva: new dhcp packages.
New packages are available:
  dhcp-4.1.2-0.5mdv2009.0
  dhcp-4.1.2-0.5mdv2010.2
  dhcp-4.1.2-0.5.20060mlcs4
  dhcp-4.1.2-0.5mdvmes5.2

RHEL: new dhcp packages.
New packages are available:
  dhcp-3.0.1-68.el4
  dhcp*-3.0.5-29.el5_7.1
  dhcp*-4.1.1-19.P1.el6_1.1

SUSE: new dhcp packages.
New packages are available, as indicated in information sources.
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