CVE-2020-28493

This affects the package jinja2 from 0.0.0 and before 2.11.3. The ReDoS vulnerability is mainly due to the _punctuation_re regex operator and its use of multiple wildcards. The last wildcard is the most exploitable as it searches for trailing punctuation. This issue can be mitigated by Markdown to format user content instead of the urlize filter, or by implementing request timeouts and limiting process memory.

Weakness

The product does not properly control the allocation and maintenance of a limited resource.

Affected Software

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/pallets/jinja/blob/ab81fd9c277900c85da0c322a2ff9d68a235b2e6/src/jinja2/utils.py%23L20
• https://github.com/pallets/jinja/pull/1343
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/PVAKCOO7VBVUBM3Q6CBBTPBFNP5NDXF4/
• https://security.gentoo.org/glsa/202107-19
• https://snyk.io/vuln/SNYK-PYTHON-JINJA2-1012994
• https://github.com/pallets/jinja/blob/ab81fd9c277900c85da0c322a2ff9d68a235b2e6/src/jinja2/utils.py%23L20
• https://github.com/pallets/jinja/pull/1343
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/PVAKCOO7VBVUBM3Q6CBBTPBFNP5NDXF4/
• https://security.gentoo.org/glsa/202107-19
• https://snyk.io/vuln/SNYK-PYTHON-JINJA2-1012994