受影响系统：

OpenBSD OpenBSD 4.2

OpenBSD OpenBSD 4.1

OpenBSD OpenBSD 4.0

描述：

BUGTRAQ ID: 25984

CVE(CAN) ID: CVE-2007-5365

OpenBSD是一款开放源代码Unix类操作系统。

OpenBSD系统的DHCP协议实现上存在缓冲区溢出漏洞，远程攻击者可能利用此漏洞控制服务器。

OpenBSD的options.c文件中的cons_options()函数没有正确地处理DHCP请求。如果远程攻击者所发送的DHCP请求中指定最大消息大小小于最小IP MTU（278）的话，就会在OpenBSD中导致dhcpd(8)覆盖栈缓冲区，执行任意指令。

漏洞存在于负责处理从客户端所接收到的DHCP选项的函数中。在src/usr.sbin/dhcpd/options.c文件中：

int

cons_options(struct packet inpacket, struct dhcp_packet outpacket,

int mms, struct tree_cache **options,

int overload, / Overload flags that may be set. /

int terminate, int bootpp, u_int8_t *prl, int prl_len)

{

unsigned char priority_list[300];

int priority_len;

unsigned char buffer[4096]; / Really big buffer... /

int main_buffer_size;

int mainbufix, bufix;

int option_size;

int length;

dhcp.h中定义了DHCP_FIXED_LEN：

if (!mms &&

inpacket &&

inpacket->options[DHO_DHCP_MAX_MESSAGE_SIZE].data &&

(inpacket->options[DHO_DHCP_MAX_MESSAGE_SIZE].len >=

sizeof(u_int16_t)))

mms = getUShort(

inpacket->options[DHO_DHCP_MAX_MESSAGE_SIZE].data);

if (mms)

main_buffer_size = mms - DHCP_FIXED_LEN;

else if (bootpp)

main_buffer_size = 64;

else

main_buffer_size = 576 - DHCP_FIXED_LEN;

if (main_buffer_size >sizeof(buffer))

main_buffer_size = sizeof(buffer);

main_buffer_size是有符型，可被攻击者控制。只要main_buffer_size是比较小的正整数（<= 4096），执行流就会正常进行：

/ Copy the options into the big buffer... /

option_size = store_options(

buffer,

(main_buffer_size - 7 ((overload & 1) ? DHCP_FILE_LEN : 0)

((overload & 2) ? DHCP_SNAME_LEN : 0)),

options, priority_list, priority_len, main_buffer_size,

(main_buffer_size ((overload & 1) ? DHCP_FILE_LEN : 0)),

terminate);

/ Put the cookie up front... /

memcpy(outpacket->options, DHCP_OPTIONS_COOKIE, 4);

mainbufix = 4;

这里如果main_buffer_size为比较小的正值的话（<= 7），就会导致store_options迅速退出，执行流会继续。具体来讲，只要客户端报文中的Maximum Segment Size值（mms）满足（DHCP_FIXED_LEN < mms < DHCP_FIXED_LEN 4）这个条件，main_buffer_size就会为小于4的正数。

if (option_size <= main_buffer_size - mainbufix) {

memcpy(&outpacket->options[mainbufix],

buffer, option_size);

mainbufix= option_size;

if (mainbufix < main_buffer_size)

outpacket->options[mainbufix] = DHO_END;

length = DHCP_FIXED_NON_UDP mainbufix;

} else {

outpacket->options[mainbufix] = DHO_DHCP_OPTION_OVERLOAD;

outpacket->options[mainbufix] = 1;

if (option_size >

main_buffer_size - mainbufix DHCP_FILE_LEN)

outpacket->options[mainbufix] = 3;

else

outpacket->options[mainbufix] = 1;

memcpy(&outpacket->options[mainbufix],

buffer, main_buffer_size - mainbufix);

用负数的第三个参数触发memcpy(3)调用就会导致覆盖大部分的进程内存。

<*来源：Gera Richarte

Nahuel Riva

链接：http://www.openbsd.org/errata40.html

http://secunia.com/advisories/27160/

http://www.openbsd.org/cgi-bin/cvsweb/src/usr.sbin/dhcpd/options.c

http://marc.info/?l=bugtraq&m=119212200825215&w=2

http://www.debian.org/security/2007/dsa-1388

*>

建议：

厂商补丁：

Debian

Debian已经为此发布了一个安全公告（DSA-1388-3）以及相应补丁:

DSA-1388-3：New dhcp packages fix arbitrary code execution

链接：http://www.debian.org/security/2007/dsa-1388

补丁下载：

Source archives:

http://security.debian.org/pool/updates/main/d/dhcp/dhcp_2.0pl5-19.5etch2.dsc

Size/MD5 checksum: 683 0b58f9e8eb121cf97c069580fe7f8d2a

http://security.debian.org/pool/updates/main/d/dhcp/dhcp_2.0pl5-19.5etch2.diff.gz

Size/MD5 checksum: 109536 e05751df16af9fef3826de1b13b19694

http://security.debian.org/pool/updates/main/d/dhcp/dhcp_2.0pl5.orig.tar.gz

Size/MD5 checksum: 294909 ab22f363a7aff924e2cc9d1019a21498

alpha architecture (DEC Alpha)

http://security.debian.org/pool/updates/main/d/dhcp/dhcp-client_2.0pl5-19.5etch2_alpha.deb

Size/MD5 checksum: 115986 5a3fad1441184f67ebfd259e225b8deb

http://security.debian.org/pool/updates/main/d/dhcp/dhcp_2.0pl5-19.5etch2_alpha.deb

Size/MD5 checksum: 122958 70cf5573cdb9df0ade56fd58963526f7

http://security.debian.org/pool/updates/main/d/dhcp/dhcp-relay_2.0pl5-19.5etch2_alpha.deb

Size/MD5 checksum: 81466 59a2774d3cbf426c116cda5b37004b02

http://security.debian.org/pool/updates/main/d/dhcp/dhcp-client-udeb_2.0pl5-19.5etch2_alpha.udeb

Size/MD5 checksum: 53328 fc6a74bbf4ca3d11266894022967d215

amd64 architecture (AMD x86_64 (AMD64))

http://security.debian.org/pool/updates/main/d/dhcp/dhcp_2.0pl5-19.5etch2_amd64.deb

Size/MD5 checksum: 115646 5fb5be9e0df58591e2f09984b107b6ff

http://security.debian.org/pool/updates/main/d/dhcp/dhcp-relay_2.0pl5-19.5etch2_amd64.deb

Size/MD5 checksum: 76622 699bdea9722e30a17d893a5fdfc59b3c

http://security.debian.org/pool/updates/main/d/dhcp/dhcp-client_2.0pl5-19.5etch2_amd64.deb

Size/MD5 checksum: 109336 aca4a6dfbe89e12da8b5f57031c6749a

http://security.debian.org/pool/updates/main/d/dhcp/dhcp-client-udeb_2.0pl5-19.5etch2_amd64.udeb

Size/MD5 checksum: 46762 b7ab045411264337a230c0e0547e976c

arm architecture (ARM)

http://security.debian.org/pool/updates/main/d/dhcp/dhcp_2.0pl5-19.5etch2_arm.deb

Size/MD5 checksum: 114446 e706691fe1b1da3e48556f3f3a2759dc

http://security.debian.org/pool/updates/main/d/dhcp/dhcp-client-udeb_2.0pl5-19.5etch2_arm.udeb

Size/MD5 checksum: 44804 a7de3008bff776bc41f57939d6baef0c

http://security.debian.org/pool/updates/main/d/dhcp/dhcp-relay_2.0pl5-19.5etch2_arm.deb

Size/MD5 checksum: 74574 c357f51c69cacd0c5e7f746735b050ee

http://security.debian.org/pool/updates/main/d/dhcp/dhcp-client_2.0pl5-19.5etch2_arm.deb

Size/MD5 checksum: 107660 c0426fafa16454f4f3613b669be104b3

hppa architecture (HP PA RISC)

http://security.debian.org/pool/updates/main/d/dhcp/dhcp_2.0pl5-19.5etch2_hppa.deb

Size/MD5 checksum: 115078 77698ad1416708c1bba42286717a6a38

http://security.debian.org/pool/updates/main/d/dhcp/dhcp-client_2.0pl5-19.5etch2_hppa.deb

Size/MD5 checksum: 109288 ba099d48d08c7b63f17c901505069a93

http://security.debian.org/pool/updates/main/d/dhcp/dhcp-relay_2.0pl5-19.5etch2_hppa.deb

Size/MD5 checksum: 77218 631787f11690111a20ca8e06da223955

http://security.debian.org/pool/updates/main/d/dhcp/dhcp-client-udeb_2.0pl5-19.5etch2_hppa.udeb

Size/MD5 checksum: 46534 e4563d516472ae7b00640c4faf63a69b

i386 architecture (Intel ia32)

http://security.debian.org/pool/updates/main/d/dhcp/dhcp-client-udeb_2.0pl5-19.5etch2_i386.udeb

Size/MD5 checksum: 40922 439ee79ca28a824a3bd702e6d2a4782a

http://security.debian.org/pool/updates/main/d/dhcp/dhcp-relay_2.0pl5-19.5etch2_i386.deb

Size/MD5 checksum: 72582 ad568458d95419eae37cbc05f7df99e0

http://security.debian.org/pool/updates/main/d/dhcp/dhcp_2.0pl5-19.5etch2_i386.deb

Size/MD5 checksum: 111342 02946828ab4646c8c9d40abbb9323f10

http://security.debian.org/pool/updates/main/d/dhcp/dhcp-client_2.0pl5-19.5etch2_i386.deb

Size/MD5 checksum: 103662 5309abf9853a42438f3b25557e2ea72a

ia64 architecture (Intel ia64)

http://security.debian.org/pool/updates/main/d/dhcp/dhcp-client_2.0pl5-19.5etch2_ia64.deb

Size/MD5 checksum: 135918 1130320929adbd7b5f6bbbdbe7ea8cf4

http://security.debian.org/pool/updates/main/d/dhcp/dhcp_2.0pl5-19.5etch2_ia64.deb

Size/MD5 checksum: 142464 88880a0d9631738e8d50d88725405f2a

http://security.debian.org/pool/updates/main/d/dhcp/dhcp-client-udeb_2.0pl5-19.5etch2_ia64.udeb

Size/MD5 checksum: 72360 4c6b9e4ed5a2b908818f2bdc047302f1

http://security.debian.org/pool/updates/main/d/dhcp/dhcp-relay_2.0pl5-19.5etch2_ia64.deb

Size/MD5 checksum: 92714 6b45e56a178149eb662b3ace829f4d1a

mips architecture (MIPS (Big Endian))

http://security.debian.org/pool/updates/main/d/dhcp/dhcp-client_2.0pl5-19.5etch2_mips.deb

Size/MD5 checksum: 112086 f3eefe99badef8981c197191cfa7ad39

http://security.debian.org/pool/updates/main/d/dhcp/dhcp_2.0pl5-19.5etch2_mips.deb

Size/MD5 checksum: 118180 bc2b4fcd3d3a7df0ece598e4a0c72ea4

http://security.debian.org/pool/updates/main/d/dhcp/dhcp-client-udeb_2.0pl5-19.5etch2_mips.udeb

Size/MD5 checksum: 49302 0a4a229e0e066b8d9fecc75125385899

http://security.debian.org/pool/updates/main/d/dhcp/dhcp-relay_2.0pl5-19.5etch2_mips.deb

Size/MD5 checksum: 78638 a588b355c89a2f5bbd893aaf938740c8

mipsel architecture (MIPS (Little Endian))

http://security.debian.org/pool/updates/main/d/dhcp/dhcp_2.0pl5-19.5etch2_mipsel.deb

Size/MD5 checksum: 117674 a39185fab632a03793efe3396311f350

http://security.debian.org/pool/updates/main/d/dhcp/dhcp-client-udeb_2.0pl5-19.5etch2_mipsel.udeb

Size/MD5 checksum: 48770 42c311ba6c2052abdddf6c2e6b7aa16a

http://security.debian.org/pool/updates/main/d/dhcp/dhcp-client_2.0pl5-19.5etch2_mipsel.deb

Size/MD5 checksum: 111554 86440305699bfed9cd6cd0721b5c032c

http://security.debian.org/pool/updates/main/d/dhcp/dhcp-relay_2.0pl5-19.5etch2_mipsel.deb

Size/MD5 checksum: 78272 95b3aff8d41ea810ee4d4b1bb75c9eed

powerpc architecture (PowerPC)

http://security.debian.org/pool/updates/main/d/dhcp/dhcp-relay_2.0pl5-19.5etch2_powerpc.deb

Size/MD5 checksum: 74674 f3377454115baffb9450fb0a0bb51d0f

http://security.debian.org/pool/updates/main/d/dhcp/dhcp-client_2.0pl5-19.5etch2_powerpc.deb

Size/MD5 checksum: 105862 4b75aabdc533969677988dbc4bd8e59e

http://security.debian.org/pool/updates/main/d/dhcp/dhcp-client-udeb_2.0pl5-19.5etch2_powerpc.udeb

Size/MD5 checksum: 43066 2edba1128225890a6792f2eecee00058

http://security.debian.org/pool/updates/main/d/dhcp/dhcp_2.0pl5-19.5etch2_powerpc.deb

Size/MD5 checksum: 112228 a60c4734706546a47127c11765f1d9bf

s390 architecture (IBM S/390)

http://security.debian.org/pool/updates/main/d/dhcp/dhcp-client-udeb_2.0pl5-19.5etch2_s390.udeb

Size/MD5 checksum: 53540 8a063f95dd410c93e6b5fe10e091fdc2

http://security.debian.org/pool/updates/main/d/dhcp/dhcp_2.0pl5-19.5etch2_s390.deb

Size/MD5 checksum: 121934 d5ae65fdd1254df11d692051753efcc8

http://security.debian.org/pool/updates/main/d/dhcp/dhcp-client_2.0pl5-19.5etch2_s390.deb

Size/MD5 checksum: 116260 29bf7983a2226601124ee0da48072aa2

http://security.debian.org/pool/updates/main/d/dhcp/dhcp-relay_2.0pl5-19.5etch2_s390.deb

Size/MD5 checksum: 80346 fe7c1452e141fc20d16653b857d6ec69

sparc architecture (Sun SPARC/UltraSPARC)

http://security.debian.org/pool/updates/main/d/dhcp/dhcp-relay_2.0pl5-19.5etch2_sparc.deb

Size/MD5 checksum: 75060 e8e5a86e2e608771e36755b0f443df83

http://security.debian.org/pool/updates/main/d/dhcp/dhcp_2.0pl5-19.5etch2_sparc.deb

Size/MD5 checksum: 112946 cd73de6703a63dc321cf788bab64d52d

http://security.debian.org/pool/updates/main/d/dhcp/dhcp-client_2.0pl5-19.5etch2_sparc.deb

Size/MD5 checksum: 106534 c777f24901a5bdb9db29c3a82da401d8

http://security.debian.org/pool/updates/main/d/dhcp/dhcp-client-udeb_2.0pl5-19.5etch2_sparc.udeb

Size/MD5 checksum: 43554 516673e6c0d38126058807dbbdf81fe7

补丁安装方法：

1. 手工安装补丁包：

首先，使用下面的命令来下载补丁软件：

wget url (url是补丁下载链接地址)

然后，使用下面的命令来安装补丁：

dpkg -i file.deb (file是相应的补丁名)

1. 使用apt-get自动安装补丁包：

首先，使用下面的命令更新内部数据库：

apt-get update

然后，使用下面的命令安装更新软件包：

apt-get upgrade

OpenBSD

目前厂商已经发布了升级补丁以修复这个安全问题，请到厂商的主页下载：

ftp://ftp.openbsd.org/pub/OpenBSD/patches/4.0/common/016_dhcpd.patch

ftp://ftp.openbsd.org/pub/OpenBSD/patches/4.1/common/010_dhcpd.patch

ftp://ftp.openbsd.org/pub/OpenBSD/patches/4.2/common/001_dhcpd.patch