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Fencer Vulns
medium 6.7

CVE-2021-43809 json

Local Code Execution through Argument Injection via dash leading git url parameter in Gemfile

published 2021-12-08 4 y ago modified 2026-11-02 6 d ago also GHSA-fj7f-vq84-fh43 , EUVD-2021-2513

cvss
6.7
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
2.9%
EPSS 2.9% chance of exploitation in 30 days, percentile 87%
public exploits
0
none known

Summary

`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.

Patch / fix

  • rubygems bundler 2.2.33
  • bundler bundler 2.2.33
  • rubygems Debian 14, Debian 13, Debian 12 3.3.5-1

debian advisories DEBIAN-CVE-2021-43809

  • ruby RHEL 8 2.5.9-114.module+el8.10.0+23088+750dc6ca
  • ruby-irb RHEL 8 2.5.9-114.module+el8.10.0+23088+750dc6ca
  • rubygems RHEL 8 2.7.6.3-114.module+el8.10.0+23088+750dc6ca
  • ruby-libs RHEL 8 2.5.9-114.module+el8.10.0+23088+750dc6ca
  • rubygem-pg RHEL 8 1.0.0-3.module+el8.9.0+19193+435404ae
  • rubygem-abrt RHEL 8 0.3.0-4.module+el8.10.0+22021+135c76a8
  • rubygem-bson RHEL 8 4.3.0-2.module+el8.9.0+19193+435404ae
  • rubygem-json RHEL 8 2.1.0-114.module+el8.10.0+23088+750dc6ca

red hat advisories RHSA-2025:7539

  • rubygem-bundler SLE Module for Basesystem 15 SP7 2.2.34-150700.21.3.1
  • rubygem-bundler SLES for SAP 15 SP3, SLES for SAP 15 SP2, SLES 15 SP4-LTSS +6 more 1.16.1-150000.3.6.1

suse advisories SUSE-SU-2026:1355-1SUSE-SU-2024:3873-1

  • ruby AlmaLinux 8 2.5.9-114.module_el8.10.0+3991+5e651d4e
  • ruby-irb AlmaLinux 8 2.5.9-114.module_el8.10.0+3991+5e651d4e
  • rubygems AlmaLinux 8 2.7.6.3-114.module_el8.10.0+3991+5e651d4e
  • ruby-libs AlmaLinux 8 2.5.9-114.module_el8.10.0+3991+5e651d4e
  • rubygem-pg AlmaLinux 8 1.0.0-3.module_el8.9.0+3635+c6f99506
  • rubygem-abrt AlmaLinux 8 0.3.0-4.module_el8.5.0+2625+ec418553
  • rubygem-bson AlmaLinux 8 4.3.0-2.module_el8.5.0+2625+ec418553
  • rubygem-bson AlmaLinux 8 4.3.0-2.module_el8.6.0+3170+4b08f9d4

almalinux advisories ALSA-2025:7539

  • ruby Rocky Linux 8 2.5.9-114.module+el8.10.0+1979+815637df
  • rubygem-pg Rocky Linux 8 1.0.0-3.module+el8.9.0+1536+5f79634e
  • rubygem-abrt Rocky Linux 8 0.3.0-4.module+el8.5.0+738+032c9c02
  • rubygem-abrt Rocky Linux 8 0.3.0-4.module+el8.9.0+1536+5f79634e
  • rubygem-bson Rocky Linux 8 4.3.0-2.module+el8.9.0+1536+5f79634e
  • rubygem-mongo Rocky Linux 8 2.5.1-2.module+el8.9.0+1536+5f79634e
  • rubygem-mysql2 Rocky Linux 8 0.4.10-4.module+el8.9.0+1536+5f79634e
  • rubygem-bundler Rocky Linux 8 1.16.1-5.module+el8.10.0+1979+815637df

rocky linux advisories RLSA-2025:7539

  • ruby-bundler Alpine 3.15 2.2.33-r0

alpine advisories ALPINE-CVE-2021-43809

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-43809 updated cvss 7.3

rubygem-bundler: unexpected code execution in Gemfiles

  • Red Hat Enterprise Linux 7 rubygem-bundler
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 8 ruby, ruby-irb, rubygems, ruby-libs, rubygem-pg, rubygem-irb, +25 more
    affected: no fix available
  • Red Hat Enterprise Linux AppStream (v. 8) ruby 2.5.9-114.module+el8.10.0+23088+750dc6ca, rubygem-pg 1.0.0-3.module+el8.9.0+19193+435404ae, ruby-irb 2.5.9-114.module+el8.10.0+23088+750dc6ca, ruby-libs 2.5.9-114.module+el8.10.0+23088+750dc6ca, rubygem-bson 4.3.0-2.module+el8.9.0+19193+435404ae, rubygem-abrt 0.3.0-4.module+el8.10.0+22021+135c76a8, +17 more
    fixed: vendor fix RHSA-2025:7539
  • Red Hat Enterprise Linux 8 ruby, ruby-irb, rubygems, ruby-libs, rubygem-pg, rubygem-irb, +25 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
6 d ago

Exploit prediction

2.91% chance of exploitation in the next 30 days, higher than 87% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/rubygems/rubygems/security/advisories/GHSA-fj7f-vq84-fh43 referenced PoC, tagged "exploit" by a source, unverified
  • sonarsource.com https://www.sonarsource.com/blog/securing-developer-tools-package-managers/ referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 6.7 CVSS:3.1/AV:L/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H
NVD 3.1 7.3 CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H
NVD 2.0 9.3 AV:N/AC:M/Au:N/C:C/I:C/A:C
GitHub 3.1 6.7 CVSS:3.1/AV:L/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H

Affected packages

ecosystem package affected fixed in
rubygems bundler
<2.2.33
2.2.33

Affected products

  • rubygems rubygems

Classification

Weakness
  • CWE-88 Improper Neutralization of Argument Delimiters in a Command

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.