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Buffer Overflows with Content

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A Process Stack

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Buffer Overflow

• Common Techniques employed in buffer overflow exploits to create backdoors– Execution of additional network services via the

INETD daemon– The addition of new users to a system– Establishing a “trust” relationship between the

victim machine and the attacker’s machine

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Example - AMD Buffer Overflow

Port 2222 is a rootshell left by the AMD exploit

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Detecting Buffer Overflows by Protocol Signatures

• Protocol Signature– Look for anomalous traffic, such as remote traffic

targeted at facilities that should not be accessible to a remote user.

• e.g. a remote user trying to connect to the Portmapperprocess

• Payload Signature– No-OP instructions to pad the exploit code– Script signatures– Abnormal user data and responses

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IMAP Buffer Overflow

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IMAP Buffer Overflow – Con’t

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IMAP Buffer Overflow – Con’t

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IMAP Buffer Overflow – Con’t

• ls –aecho “+ + ”> /.rhosts

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NO-OP Hex Code Based on Processor Type

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Script Signatures – NO-OP Overflow

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Script Signatures – NO-OP Overflow Con’t

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Script Signatures – NO-OP Overflow Con’t

• This frame shows a large number of hex 90s followed by some machine code, some ASCII strings, and a literal command /bin/sh -c

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Abnormal ResponsesFTP Authentication Buffer Overflow – FTPD exploit

The password supplied in response to the FTPD prompt is suspiciously large

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Defending Against Buffer Overflows

• strcpy and strncpy• Introduce bounds checking into C programs• Stack-based buffer overflow - CPU executes

code that is resident on the stack– Only code in the code space can be executed

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Fragmentation

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Fragmentation

• Attackers can use fragmentation to mask their probes and exploits

• Fragment offset is specified as a quantity of 8-byte chunk– The size of all legal nonterminal fragments must

be multiples of 8 bytes• Any fragmented packets with a byte size

divisible by 8, except for the last one

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Boink Attack

•IP stack has no concept of negative math

•Availability DoS

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Teardrop Attack

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evilPing

….

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evilPing

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Modified Ping of Death

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Modified Ping of Death

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CGI Scan

•The attacker is running a script that attempts a number of Web server exploits, such as /cgi-bin/rwwwshell.pl

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CGI Scan – Con’t

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PHF Attack

CVE-1999-0067

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Some Example CGI CVE Entries

• CVE-1999-0068– CGI PHP mylog script allows an attacker to read any file

on the target server. • CVE-1999-0467

– The Webcom CGI Guestbook programs wguest.exe and rguest.exe allow a remote attacker to read arbitrary files using the "template" parameter

• CVE-1999-0509– Perl, sh, csh, or other shell interpreters are installed in the

cgi-bin directory on a WWW site, which allows remote attackers to execute arbitrary commands.

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SGI IRIX Object Server

• CVE-2000-0245• A vulnerability in an SGI IRIX object server

daemon– Allow remote attackers to create user accounts– Port 5135: the SGI object server

• Scan one to goodguy-a.com yields nothing

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SGI Object Server – Con’t• The scan to goodguy-b.com is a bust

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SGI Object Server – Con’t• The start of the bad guy

• The user zippy is added