Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Multipart::Parser extracts the boundary parameter from multipart/form-data using a greedy regular expression. When a Content-Type header contains multiple boundary parameters, Rack selects the last one rather than the first.
In deployments where an upstream proxy, WAF, or intermediary interprets the first boundary parameter, this mismatch can allow an attacker to smuggle multipart content past upstream inspection and have Rack parse a different body structure than the intermediary validated. This issue has been patched in versions 2.2.23, 3.1.21, and 3.2.6.
Attack Parameters
Attack Vector
Network
Can be exploited remotely
Attack Complexity
Low
Easy to exploit
Privileges Required
None
No privileges needed
User Interaction
None
No user interaction needed
Impact Assessment
Confidentiality
None
No data leak
Integrity
Low
Partial data modification
Availability
None
No disruption
CVSS Vector v3.1
Weakness Type (CWE)
Vulnerable Products 3
| Configuration | From (including) | Up to (excluding) |
|---|---|---|
|
Rack Rack
cpe:2.3:a:rack:rack:*:*:*:*:*:ruby:*:*
|
— |
2.2.23
|
|
Rack Rack
cpe:2.3:a:rack:rack:*:*:*:*:*:ruby:*:*
|
3.0.0
|
3.1.21
|
|
Rack Rack
cpe:2.3:a:rack:rack:*:*:*:*:*:ruby:*:*
|
3.2.0
|
3.2.6
|