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Symbolic links in an unpacking routine may enable attackers to read and/or write to arbitrary locations in dbdeployer

Moderate severity GitHub Reviewed Published Dec 17, 2020 in datacharmer/dbdeployer • Updated Feb 1, 2023

Package

gomod github.com/datacharmer/dbdeployer (Go)

Affected versions

< 1.58.2

Patched versions

1.58.2

Description

Impact

Users unpacking a tarball through dbdeployer may use a maliciously packaged tarball that contains symlinks to files external to the target. In such scenario, an attacker could induce dbdeployer to write into a system file, thus altering the computer defences.

Mitigating factors

For the attach to succeed, the following factors need to contribute:

  • The user is logged in as root. While dbdeployer is usable as root, it was designed to run as unprivileged user.
  • The user has taken a tarball from a non secure source, without testing the checksum. When the tarball is retrieved through dbdeployer, the checksum is compared before attempting to unpack.

Analysis

An attacker could inject a symbolic link into the tarball, so that a file could result into fake_file -> /etc/passwd or some equally important file.
As it is now, dbdeployer would create the symlink as defined, with a local file fake_file linked to /etc/passwd. The danger here is that any process with the privileges to write to both fake_file and /etc/passwd could overwrite the system file. Even without malicious intent, this could result in the system to become unusable.
As noted above, the user must have write privileges to the target file to do the damage.

Remedies

It has been suggested that the extract procedure use filepath.EvalSymlinks to determine whether the target is within the extraction directory. Unfortunately, this approach is unavailable in this context, because it would prevent legitimate patterns from being carried out.
A simple case is a file mysql-8.0.22-macos10.15-x86_64/bin/libprotobuf-lite.3.11.4.dylib with a linkName ../lib/libprotobuf-lite.3.11.4.dylib, if the linked file has not been created yet, filepath.EvalSymlinks would fail, as it acts on existing files only.

An alternative method is comparing the depth (how many directories) of the file name with the depth of the link name. If the link name has a higher depth than the local file, we block the operation with an appropriate error:

Unpacking tarball exploit/mysql-8.0.22-macos10.15-x86_64.tar.gz to $HOME/opt/mysql/test8.0.22
......
link '../../../../../../../../../../etc' points outside target directory

exit status 1

As an additional fortifier, we can check whether the link points to an existing file, calculate its absolute name, and compare it with the absolute name of the extraction directory. A link to a full path (such as /etc/passwd) would fail this test, and trigger an error.

The same check can be applied to a link to a non existing file with absolute path.

Patches

Patched in release 1.58.2

For more information

If you have any questions or comments about this advisory:

References

@datacharmer datacharmer published to datacharmer/dbdeployer Dec 17, 2020
Published by the National Vulnerability Database Dec 21, 2020
Reviewed May 21, 2021
Published to the GitHub Advisory Database Feb 12, 2022
Last updated Feb 1, 2023

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 v3 base metrics

Attack vector
Network
Attack complexity
High
Privileges required
None
User interaction
Required
Scope
Changed
Confidentiality
None
Integrity
High
Availability
None

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:N/AC:H/PR:N/UI:R/S:C/C:N/I:H/A:N

EPSS score

0.064%
(29th percentile)

Weaknesses

CVE ID

CVE-2020-26277

GHSA ID

GHSA-47wr-426j-fr82

Source code

No known source code

Credits

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