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Improper Verification of Cryptographic Signature in django-rest-registration

Critical severity GitHub Reviewed Published Jul 1, 2019 in apragacz/django-rest-registration • Updated Sep 16, 2024

Package

pip django-rest-registration (pip)

Affected versions

>= 0.2.0, < 0.5.0

Patched versions

0.5.0

Description

Misusing the Django Signer API leads to predictable signatures used in verification emails

Impact

The vulnerability is a high severity one. Anyone using Django REST Registration library versions 0.2.* - 0.4.* with e-mail verification option (which is recommended, but needs additional configuration) is affected.
In the worst case, the attacker can take over any Django user by resetting his/her password without even receiving the reset password verification link, just by guessing the signature from publicly available data (more detailed description below).

Patches

The problem has been patched in version 0.5.0. All library users should upgrade to version 0.5.0 or higher.
The fix will invalidate all previously generated signatures , and in consequence, all verification links in previously sent verification e-mails. Therefore semi-major version 0.5.0 was released instead of version 0.4.6 to mark that incompatibility.

Workarounds

The easiest way way is to disable the verification options by using something like the minimal configuration described here. This will unfortunately disable checking whether the given e-mail is valid and make unable to users who registered an account but didn't verify it before config change.

Less harsh way is to temporarily disable just the the reset password functionality:

REST_REGISTRATION = {
    # ...
    'RESET_PASSWORD_VERIFICATION_ENABLED': False,
    # ...
}

Which should disallow the worst case, which is account takeover by an attacker. The attacker can still use the register-email endpoint to change the email to its own (but it is less critical than resetting the password in this case).

If one already set 'RESET_PASSWORD_VERIFICATION_ONE_TIME_USE' setting key to True in REST_REGISTRATION Django setting (which is not the default setting) then it should mitigate the security issue in case of password reset (in this case, the signature is much harder to guess by the attacker). But even in this case upgrade to newest version is highly recommended.

Technical description

After the code was refactored to use the official Signer class the salt
was passed wrongly as secret key, replacing the SECRET_KEY set in
Django settings file. This leads to the Django SECRET_KEY not being used by the signer object. The secret key of the signer ends to be the salt which in most cases is a static string which is publicly available.

In consequence this allows, with verification enabled, to guess
the signature contained in the verification link (which is sent in a verification e-mail) by a potential attacker very easily.

The bug went unnoticed for very long time so multiple versions are affected:
this bug affects versions 0.2.*, 0.3.*, 0.4.*; version 0.1.* is not affected.

Recently released version 0.5.0 contains the fix which correctly passes the salt to the Signer constructor as keyword argument instead as a positonal argument. It also contains additonal test so this problem should not reappear in the future.

Thanks

I'd like to thank @peterthomassen from https://desec.io DNS security project for finding the bug. I'd like also to thank his employer, SSE (https://www.securesystems.de) for funding his work.

For more information

If you have any questions or comments about this advisory:

References

@apragacz apragacz published to apragacz/django-rest-registration Jul 1, 2019
Published to the GitHub Advisory Database Jul 2, 2019
Reviewed Jun 16, 2020
Last updated Sep 16, 2024

Severity

Critical

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Network
Attack Complexity Low
Attack Requirements None
Privileges Required None
User interaction None
Vulnerable System Impact Metrics
Confidentiality High
Integrity High
Availability High
Subsequent System Impact Metrics
Confidentiality None
Integrity None
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

EPSS score

1.217%
(86th percentile)

Weaknesses

CVE ID

CVE-2019-13177

GHSA ID

GHSA-p3w6-jcg4-52xh

Source code

Credits

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