id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
20760	Account enumeration through timing attack in password verification in django.contrib.auth	jpaglier@…	Aymeric Augustin	"This bug is an example of http://cwe.mitre.org/data/definitions/208.html and very similar to https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2004-1602 .

Description
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When attempting to authenticate using django.contrib.auth, if a user does not exist the authenticate() function returns None nearly instantaneously, while when a user exists it takes much longer as the attempted password gets hashed and compared with the stored password. This allows for an attacker to infer whether or not a given account exists based upon the response time of an authentication attempt.

This can be seen much more clearly when the number of rounds on the password hasher is set to something high like 100000.

Mitigation
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In authenticate(), create a dummy user and set its password. If no user is returned from the database query, check a password which is guaranteed not to match against the dummy.

Note
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This mitigation strategy does not entirely mitigate a timing attack of this fashion. It does, however, greatly increase the amount of work required to gain usable information from it. For example, with a smaller variation between the two cases (user exists, user does not exist), the differences in lengths of time become much harder to distinguish from network transit times."	Bug	closed	contrib.auth	1.5	Normal	fixed	security authentication timing enumeration	jpaglier@… eromijn@…	Ready for checkin	1	0	0	0	0	0