fpdf2 is a PDF creation library for Python. From 2.5.0 until 2.8.8, fpdf2s SVGObject.build_xref() passes nested SVG references to GraphicsContext.add_item(), whose default clone=True deep-copy behavior copies the complete referenced graphics tree during FPDF.image() processing. Repeating references at each nesting level makes the in-memory object count and processing work grow exponentially, allowing a small user-controlled SVG to consume excessive CPU and memory, raise MemoryError, fail PDF generation jobs, and reduce or exhaust worker capacity. ResourceAccessPolicy does not prevent the issue because the references are inline and require no external resource, XML entity, local file, or permissive network setting. This issue is fixed in version 2.8.8.
Weakness
The product does not properly control the allocation and maintenance of a limited resource.
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
References
- https://github.com/py-pdf/fpdf2/commit/d7bd1061205d50da6a541dadfdb9d66beb763f2f
- https://github.com/py-pdf/fpdf2/pull/1889
- https://github.com/py-pdf/fpdf2/releases/tag/2.8.8
- https://github.com/py-pdf/fpdf2/security/advisories/GHSA-wqw6-wpr3-45rh
- https://github.com/py-pdf/fpdf2/security/advisories/GHSA-wqw6-wpr3-45rh