Detections
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Linux Distros Unpatched Vulnerability : CVE-2021-43809

high Nessus Plugin ID 224238

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Synopsis

The Linux/Unix host has one or more packages installed with a vulnerability that the vendor indicates will not be patched.

Description

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

 - `Bundler` is a package for managing application dependencies in Ruby. In `bundler` versions before 2.2.33, when working with untrusted and apparently harmless `Gemfile`'s, it is not expected that they lead to execution of external code, unless that's explicit in the ruby code inside the `Gemfile` itself. However, if the `Gemfile` includes `gem` entries that use the `git` option with invalid, but seemingly harmless, values with a leading dash, this can be false. To handle dependencies that come from a Git repository instead of a registry, Bundler uses various commands, such as `git clone`. These commands are being constructed using user input (e.g. the repository URL). When building the commands, Bundler versions before 2.2.33 correctly avoid Command Injection vulnerabilities by passing an array of arguments instead of a command string. However, there is the possibility that a user input starts with a dash (`-`) and is therefore treated as an optional argument instead of a positional one. This can lead to Code Execution because some of the commands have options that can be leveraged to run arbitrary executables. Since this value comes from the `Gemfile` file, it can contain any character, including a leading dash. To exploit this vulnerability, an attacker has to craft a directory containing a `Gemfile` file that declares a dependency that is located in a Git repository. This dependency has to have a Git URL in the form of `-u./payload`. This URL will be used to construct a Git clone command but will be interpreted as the upload-pack argument. Then this directory needs to be shared with the victim, who then needs to run a command that evaluates the Gemfile, such as `bundle lock`, inside. This vulnerability can lead to Arbitrary Code Execution, which could potentially lead to the takeover of the system. However, the exploitability is very low, because it requires a lot of user interaction. Bundler 2.2.33 has patched this problem by inserting `--` as an argument before any positional arguments to those Git commands that were affected by this issue. Regardless of whether users can upgrade or not, they should review any untrustred `Gemfile`'s before running any `bundler` commands that may read them, since they can contain arbitrary ruby code. (CVE-2021-43809)

Note that Nessus relies on the presence of the package as reported by the vendor.

Solution

There is no known solution at this time.

See Also

https://access.redhat.com/security/cve/cve-2021-43809

https://ubuntu.com/security/CVE-2021-43809

Plugin Details

Severity: High

ID: 224238

File Name: unpatched_CVE_2021_43809.nasl

Version: 1.2

Type: local

Agent: unix

Family: Misc.

Published: 3/5/2025

Updated: 8/20/2025

Supported Sensors: Agentless Assessment, Frictionless Assessment Agent, Frictionless Assessment AWS, Frictionless Assessment Azure, Nessus Agent, Nessus

Risk Information

VPR

Risk Factor: Medium

Score: 6.7

CVSS v2

Risk Factor: High

Base Score: 9.3

Temporal Score: 7.3

Vector: CVSS2#AV:N/AC:M/Au:N/C:C/I:C/A:C

CVSS Score Source: CVE-2021-43809

CVSS v3

Risk Factor: High

Base Score: 7.3

Temporal Score: 6.6

Vector: CVSS:3.0/AV:L/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H

Temporal Vector: CVSS:3.0/E:P/RL:O/RC:C

Vulnerability Information

CPE: cpe:/o:canonical:ubuntu_linux:20.04:-:lts, cpe:/o:canonical:ubuntu_linux:16.04:-:lts, cpe:/o:canonical:ubuntu_linux:18.04:-:lts, p-cpe:/a:redhat:enterprise_linux:rubygem-bundler-doc, p-cpe:/a:canonical:ubuntu_linux:bundler, cpe:/o:centos:centos:8, p-cpe:/a:centos:centos:rubygem-bundler, p-cpe:/a:redhat:enterprise_linux:ruby, p-cpe:/a:centos:centos:rubygem-bundler-doc, p-cpe:/a:redhat:enterprise_linux:rubygem-bundler, p-cpe:/a:centos:centos:ruby, cpe:/o:redhat:enterprise_linux:8

Required KB Items: Host/OS/identifier, Host/cpu, Host/local_checks_enabled, global_settings/vendor_unpatched

Exploit Available: true

Exploit Ease: Exploits are available

Vulnerability Publication Date: 12/8/2021

Reference Information

CVE: CVE-2021-43809