pypdf is a free and open-source pure-python PDF library. Prior to 6.21.3, pypdf can consume excessive time and memory when an application accesses the page count of a crafted encrypted PDF whose page tree declares a forged /Count value. Even after successful decryption, page-count retrieval trusts the unvalidated declared count instead of walking the page tree, allowing the attacker-controlled value to drive excessive work and memory use. This issue is fixed in version 6.21.3.
Weakness
The product does not properly control the allocation and maintenance of a limited resource.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Pypdf | Py-pdf | * | 6.21.3 (excluding) |
Potential Mitigations
Mitigation of resource exhaustion attacks requires that the target system either:
The first of these solutions is an issue in itself though, since it may allow attackers to prevent the use of the system by a particular valid user. If the attacker impersonates the valid user, they may be able to prevent the user from accessing the server in question.
The second solution is simply difficult to effectively institute – and even when properly done, it does not provide a full solution. It simply makes the attack require more resources on the part of the attacker.
Related Attack Patterns
- https://cwe.mitre.org/data/definitions/147.html
- https://cwe.mitre.org/data/definitions/227.html
- https://cwe.mitre.org/data/definitions/492.html