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sudo-rs Session File Relative Path Traversal vulnerability

Low severity GitHub Reviewed Published Sep 21, 2023 in trifectatechfoundation/sudo-rs • Updated Nov 6, 2023

Package

cargo sudo-rs (Rust)

Affected versions

<= 0.2.0

Patched versions

0.2.1

Description

Background

Sudo-rs allows users to not have to enter authentication at every sudo attempt, but instead only requiring authentication every once in a while in every terminal or process group. Only once a configurable timeout has passed will the user have to re-authenticate themselves. Supporting this functionality is a set of session files (timestamps) for each user, stored in /var/run/sudo-rs/ts. These files are named according to the username from which the sudo attempt is made (the origin user).

Impact

An issue was discovered where usernames containing the . and / characters could result in the corruption of specific files on the filesystem. As usernames are generally not limited by the characters they can contain, a username appearing to be a relative path can be constructed. For example we could add a user to the system containing the username ../../../../bin/cp. When logged in as a user with that name, that user could run sudo -K to clear their session record file. The session code then constructs the path to the session file by concatenating the username to the session file storage directory, resulting in a resolved path of /bin/cp. The code then clears that file, resulting in the cp binary effectively being removed from the system.

An attacker needs to be able to login as a user with a constructed username. Given that such a username is unlikely to exist on an existing system, they will also need to be able to create the users with the constructed usernames.

Patches

The bug is fixed in version 0.2.1 of sudo-rs. Sudo-rs now uses the uid for the user instead of their username for determining the filename. Note that an upgrade to this version will result in existing session files being ignored and users will be forced to re-authenticate. It also fully eliminates any possibility of path traversal, given that uids are always integer values.

Workarounds

The sudo -K and sudo -k commands can run, even if a user has no sudo access. Make sure that your system does not contain any users with a specially crafted username. While this is the case and while untrusted users do not have the ability to create arbitrary users on your system you should not be able to exploit this issue.

References

@rnijveld rnijveld published to trifectatechfoundation/sudo-rs Sep 21, 2023
Published by the National Vulnerability Database Sep 21, 2023
Published to the GitHub Advisory Database Sep 21, 2023
Reviewed Sep 21, 2023
Last updated Nov 6, 2023

Severity

Low

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 v3 base metrics

Attack vector
Local
Attack complexity
Low
Privileges required
High
User interaction
Required
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
Low

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:L/AC:L/PR:H/UI:R/S:U/C:N/I:L/A:L

EPSS score

0.117%
(46th percentile)

CVE ID

CVE-2023-42456

GHSA ID

GHSA-2r3c-m6v7-9354

Source code

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