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PAM module may allow accessing with the credentials of another user

High severity GitHub Reviewed Published Oct 3, 2024 in ubuntu/authd • Updated Oct 3, 2024

Package

gomod github.com/ubuntu/authd (Go)

Affected versions

< 0.0.0-20240930103526-63e527496b01

Patched versions

0.0.0-20240930103526-63e527496b01

Description

Authd PAM module up to version 0.3.4 can allow broker-managed users to impersonate any other user managed by the same broker and perform any PAM operation with it, including authenticating as them.

This is possible using tools such as su, sudo or ssh (and potentially others) that, so far, do not ensure that the PAM user at the end of the transaction is matching the one who initiated the transaction.

Authd 0.3.5 fixes this by not allowing changing the user unless it was never set before in the PAM stack.

su version that will include util-linux/util-linux#3206 will not be affected
ssh version that will include openssh/openssh-portable#521 will not be affected
sudo version that will include sudo-project/sudo#412 will not be affected
login not affected
passwd not affected

Old report

Summary

An user can access as another user using its own credentials

Details

I feel we’ve a security issue that is due to the fact that we allow changing the user in the cases in which that’s already provided by PAM, I’ve not tested this using the entra-id broker but it’s reproducible with the example one, but unless I’m missing something it should be independent from the broker in use.

Basically, by going to the user selection page we allow to login as any user by entering the use own credentials.

See for example: https://asciinema.org/a/VIcjpDImomaGu0wxsJJxNdmlf or https://asciinema.org/a/CV3D1gaEhn2yclqSMKCnifYPo

Basically it’s possible to logging in as user1 using the credentials of user2 or user3.

The issue doesn’t affect login or passwd, but it does affect su and sshd, since in both cases they don’t check if the PAM_USER changed before the final authentication.

Now, while those tools should likely be fixed to only read the PAM_USER once pam gave them the final ok, I think authd should not allow changing the user at all when it has been provided by PAM.

### References - https://github.com/ubuntu/authd/security/advisories/GHSA-x5q3-c8rm-w787 - https://nvd.nist.gov/vuln/detail/CVE-2024-9313 - https://github.com/ubuntu/authd/commit/63e527496b013bed46904c1c58be593c13ebdce5 - https://www.cve.org/CVERecord?id=CVE-2024-9313
@didrocks didrocks published to ubuntu/authd Oct 3, 2024
Published by the National Vulnerability Database Oct 3, 2024
Published to the GitHub Advisory Database Oct 3, 2024
Reviewed Oct 3, 2024
Last updated Oct 3, 2024

Severity

High

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 Low
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:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Weaknesses

CVE ID

CVE-2024-9313

GHSA ID

GHSA-x5q3-c8rm-w787

Source code

Credits

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