CVE-2021-21240

httplib2 is a comprehensive HTTP client library for Python. In httplib2 before version 0.19.0, a malicious server which responds with long series of xa0 characters in the www-authenticate header may cause Denial of Service (CPU burn while parsing header) of the httplib2 client accessing said server. This is fixed in version 0.19.0 which contains a new implementation of auth headers parsing using the pyparsing library.

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/httplib2/httplib2/commit/bd9ee252c8f099608019709e22c0d705e98d26bc
• https://github.com/httplib2/httplib2/pull/182
• https://github.com/httplib2/httplib2/security/advisories/GHSA-93xj-8mrv-444m
• https://pypi.org/project/httplib2
• https://github.com/httplib2/httplib2/commit/bd9ee252c8f099608019709e22c0d705e98d26bc
• https://github.com/httplib2/httplib2/pull/182
• https://github.com/httplib2/httplib2/security/advisories/GHSA-93xj-8mrv-444m
• https://pypi.org/project/httplib2