FirstBlood-#736 — [COLLAB] Phar deserialization to RCE via upload vaccination proof
This issue was discovered on FirstBlood v2.0.0 (issues patched)
On 2021-10-27, amec0e Level 3 reported:
After a bit help on the issue and looking at a previously disclosed hackerone report i was finally able to get the phar deserialization to remote code execution via the endpoint
/vaccination-manager/pub/upload-vaccination-proof.phpusing phpggc we can create a jpg serialized payload to embed into a legitimate jpg image and upload this. Then using the
proof=parameter on the endpoint
/api/checkproof.php?which is checking that a file exists we can use
phar://to deserialize our payload and execute our code.
(This is my current understanding of this, which may not be entirely correct)
Insecure Deserialization to Remote Code Execution. Remote code execution allows a attacker to execute malicious code on the target server with the permissions of the current user (usually www-data).
Steps to Reproduce:
- Get phpggc from Github
- Get a regular jpg image (I used barker-logo.jpg)
- Generate the serialized payload using the following:
./phpggc -pj barker_logo.jpg -o /tmp/rce.jpg monolog/rce1 system id
We can also verify our payload embedded inside the image using
Now to continue.
- Open Burpsuite and make sure "Intercept is off"
- Visit the endpoint
/vaccination-manager/pub/upload-vaccination-proof.phpand Select your Image rce.jpg and enter a email and click "Upload"
- In burpsuite Proxy > HTTP history right click the recent GET request to the endpoint
/api/checkproof.php?proof=/app/firstblood/upload/blob.jpgand click "Send to Repeater"
- Viewing the request in repeater append
phar://to the enpoint
/app/firstblood/upload/blob.jpgand click "Send".
You should now receive a reponse showing the current id of the user.
In Collaboration with thebinarybot
FirstBlood ID: 34
Vulnerability Type: Deserialization
This endpoint calls filesize() on the path provided in the 'proof' param with no filtering or sanitisation. By adding the phar:// stream handler to the path, an attacker can force a previously uploaded file to be sent through deserialisation. Coupled with the fact that a gadget-chain vulnerable version of monolog is being used, this allows for RCE.