Bref is an open-source project that helps users go serverless on Amazon Web Services with PHP. When Bref prior to version 2.1.17 is used with the Event-Driven Function runtime and the handler is a `RequestHandlerInterface`, then the Lambda event is converted to a PSR7 object. During the conversion process, if the request is a MultiPart, each part is parsed. In the parsing process, the `Content-Type` header of each part is read using the `Riverline/multipart-parser` library. The library, in the `StreamedPart::parseHeaderContent` function, performs slow multi-byte string operations on the header value. Precisely, the `mb_convert_encoding` function is used with the first (`$string`) and third (`$from_encoding`) parameters read from the header value. An attacker could send specifically crafted requests which would force the server into performing long operations with a consequent long billed duration. The attack has the following requirements and limitations: The Lambda should use the Event-Driven Function runtime and the `RequestHandlerInterface` handler and should implement at least an endpoint accepting POST requests; the attacker can send requests up to 6MB long (this is enough to cause a billed duration between 400ms and 500ms with the default 1024MB RAM Lambda image of Bref); and if the Lambda uses a PHP runtime <= php-82, the impact is higher as the billed duration in the default 1024MB RAM Lambda image of Bref could be brought to more than 900ms for each request. Notice that the vulnerability applies only to headers read from the request body as the request header has a limitation which allows a total maximum size of ~10KB. Version 2.1.17 contains a fix for this issue.
| Métrique | Valeur | Interprétation |
|---|---|---|
|
AV (Vecteur d'Attaque)
Attack Vector
|
Network (N)
|
Exploit possible à distance via réseau (HTTP, API, etc.) |
|
AC (Complexité d'Attaque)
Attack Complexity
|
Low (L)
|
Peu de conditions requises pour exploiter |
|
PR (Privilèges Requis)
Privileges Required
|
None (N)
|
Aucune authentification requise |
|
UI (Interaction Utilisateur)
User Interaction
|
None (N)
|
Aucune interaction utilisateur nécessaire |
|
S (Périmètre)
Scope
|
Unchanged (U)
|
Impact reste dans le périmètre du composant compromis |
|
C (Impact Confidentialité)
Confidentiality Impact
|
None (N)
|
Aucune divulgation d'informations |
|
I (Impact Intégrité)
Integrity Impact
|
None (N)
|
Aucune modification de données possible |
|
A (Impact Disponibilité)
Availability Impact
|
Low (L)
|
Interruption partielle du service possible |
Slow String Operations via MultiPart Requests in Event-Driven Functions
Slow String Operations via MultiPart Requests in Event-Driven Functions