Local Code Execution through Argument Injection via dash leading git url parameter in Gemfile (CVE-2021-43809)
Published Last modified Sources: CVE.org, Debian LTS, OSV
What is affected, what to do
`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.
An exploit is publicly available. Update Rubygems to version 2.2.33.
- Affected
- Rubygems
lt *..2.2.33
- Rubygems
- Fixed in
- Rubygems
2.2.33
- Rubygems
Not sure whether and how you are affected? Ask a question about this vulnerability
Metrics
7.3
Priority
XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.
Source: NVD, CVSS v3
6.7
CVSS v3
Severity Medium on the scale from 0 to 10.
Source: CVE.org, Debian LTS, OSV
2.9 %
EPSS score
Moderate — model estimates 1-10% exploitation likelihood.
Source: FIRST EPSS, percentile 87.0
Show all metrics
- Severity
- High
Priority (0–325)
The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?
Read in glossary- 94.18 Methodology
Exploit maturity
An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.
Read in glossary- PoC (publicly reported)
XIEM Effective CVSS
XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.
Read in glossary- 7.3 Methodology
CVSS v3
CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.
Read in glossary- 6.7
EPSS score
The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.
Read in glossary- 2.9 %
- Moderate — model estimates 1-10% exploitation likelihood.
EPSS percentile
The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.
Read in glossary- 87.0
- Critical — this CVE ranks in the top fifth of all CVEs scored today (rank ≥ 80%).
KEV status
The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.
Read in glossary- —
- Published
- CISA assessment (SSVC)
- Exploitation: none known · not automatable · Technical impact: partial
- Source: CISA Vulnrichment, as of 2 November 2026
CWE
CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.
Read in glossary- CWE-88
Detection rules
No NEOSEC detection rule is available for this vulnerability yet.
Classification under NIS2 and CRA
Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.
NIS2
NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.
Read in glossary- High technical severity: assess and remediate the vulnerability in vulnerability handling under Art. 21(2)(e) NIS2 and document the decision.
CRA
The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.
Read in glossary- From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
ISO/IEC 27001
ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.
Read in glossary- Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.
Description
`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.
Source: cvelistv5, NVD (NIST), Debian LTS Advisories, OSV (Open Source Vulnerabilities)
Affected products
The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.
| Affected versions | Fixed in | ||
|---|---|---|---|
| rubygems | rubygems |
|
|
| bundler | bundler |
|
|
| rubygems | bundler |
|
|
Vendors and products
Affected operating systems
| Linux | debian | rubygems | bullseye |
Weakness classes (CWE)
CWE-88Improper Neutralization of Argument Delimiters in a Command ('Argument Injection')
Base
The product constructs a string for a command to be executed by a separate component in another control sphere, but it does not properly delimit the intended arguments, options, or switches within that command string.
Entry at MITRE CWE-88
Public exploit references
Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.
| Reference tagged as exploit | github.com (opens in a new tab) | PoC (publicly reported)reported, not verified | — |
References & sources
- github.comrubygems/rubygems/security/advisories/GHSA-fj7f-vq84-fh43web, x_refsource_CONFIRM, Exploit, Vendor advisory
- NVD (NIST)vuln/detail/CVE-2021-43809advisory
- github.comrubygems/rubygems/pull/5142web, x_refsource_MISC, Patch
- github.comrubygems/rubygems/commit/0fad1ccfe9dd7a3c5b82c1496df3c2b4842870…web, x_refsource_MISC, Patch
- github.comrubygems/rubygems/commit/a4f2f8ac17e6ce81c689527a8b6f14381060d9…web, x_refsource_MISC, Patch
- github.comrubygems/rubygemspackage
- github.comrubysec/ruby-advisory-db/blob/master/gems/bundler/CVE-2021-4380…web
- lists.debian.orgdebian-lts-announce/2025/05/msg00015.htmlweb
- sonarsource.comblog/securing-developer-tools-package-managersweb
- sonarsource.comblog/securing-developer-tools-package-managersx_refsource_MISC, Exploit, Mitigation
Changes to this CVE
Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).
Record modifiedCISA ADP
CISA assessment (SSVC): exploitation: none known, automatable: no
Show the original change
Individual changes of this event as published by NVD Type Action Before After SSVC assessment added —{"id":"CVE-2021-43809","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"no"},{"technicalImpact":"partial"}],"version":"2.0.3","timestamp":"2026-11-02T18:14:04.647739Z"}Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0
Record modifiedCVE Program
New references:- https://github.com/rubygems/rubygems/commit/0fad1ccfe9dd7a3c5b82c1496df3c2b4842870d3
- https://github.com/rubygems/rubygems/commit/a4f2f8ac17e6ce81c689527a8b6f14381060d95f
- https://github.com/rubygems/rubygems/pull/5142
- https://github.com/rubygems/rubygems/security/advisories/GHSA-fj7f-vq84-fh43
and 2 more references
Show 17 original changes
Individual changes of this event as published by NVD Type Action Before After Reference added —https://github.com/rubygems/rubygems/commit/0fad1ccfe9dd7a3c5b82c1496df3c2b4842870d3Reference added —https://github.com/rubygems/rubygems/commit/a4f2f8ac17e6ce81c689527a8b6f14381060d95fReference added —https://github.com/rubygems/rubygems/pull/5142Reference added —https://github.com/rubygems/rubygems/security/advisories/GHSA-fj7f-vq84-fh43Reference added —https://lists.debian.org/debian-lts-announce/2025/05/msg00015.htmlReference added —https://www.sonarsource.com/blog/securing-developer-tools-package-managers/Reference removed https://github.com/rubygems/rubygems/commit/0fad1ccfe9dd7a3c5b82c1496df3c2b4842870d3—Reference removed https://github.com/rubygems/rubygems/commit/a4f2f8ac17e6ce81c689527a8b6f14381060d95f—Reference removed https://github.com/rubygems/rubygems/pull/5142—Reference removed https://github.com/rubygems/rubygems/security/advisories/GHSA-fj7f-vq84-fh43—Reference removed https://lists.debian.org/debian-lts-announce/2025/05/msg00015.html—Reference removed https://www.sonarsource.com/blog/securing-developer-tools-package-managers/—Reference type removed https://github.com/rubygems/rubygems/commit/0fad1ccfe9dd7a3c5b82c1496df3c2b4842870d3 Types: Patch—Reference type removed https://github.com/rubygems/rubygems/commit/a4f2f8ac17e6ce81c689527a8b6f14381060d95f Types: Patch—Reference type removed https://github.com/rubygems/rubygems/pull/5142 Types: Patch—Reference type removed https://github.com/rubygems/rubygems/security/advisories/GHSA-fj7f-vq84-fh43 Types: Exploit, Vendor Advisory—Reference type removed https://www.sonarsource.com/blog/securing-developer-tools-package-managers/ Types: Exploit, Mitigation—Source identifier: af854a3a-2127-422b-91ae-364da2661108
Record modifiedGitHub
New references:- https://github.com/rubygems/rubygems/commit/0fad1ccfe9dd7a3c5b82c1496df3c2b4842870d3
- https://github.com/rubygems/rubygems/commit/a4f2f8ac17e6ce81c689527a8b6f14381060d95f
- https://github.com/rubygems/rubygems/pull/5142
- https://github.com/rubygems/rubygems/security/advisories/GHSA-fj7f-vq84-fh43
and 1 more reference
Show 15 original changes
Individual changes of this event as published by NVD Type Action Before After Reference added —https://github.com/rubygems/rubygems/commit/0fad1ccfe9dd7a3c5b82c1496df3c2b4842870d3Reference added —https://github.com/rubygems/rubygems/commit/a4f2f8ac17e6ce81c689527a8b6f14381060d95fReference added —https://github.com/rubygems/rubygems/pull/5142Reference added —https://github.com/rubygems/rubygems/security/advisories/GHSA-fj7f-vq84-fh43Reference added —https://www.sonarsource.com/blog/securing-developer-tools-package-managers/Reference removed https://github.com/rubygems/rubygems/commit/0fad1ccfe9dd7a3c5b82c1496df3c2b4842870d3—Reference removed https://github.com/rubygems/rubygems/commit/a4f2f8ac17e6ce81c689527a8b6f14381060d95f—Reference removed https://github.com/rubygems/rubygems/pull/5142—Reference removed https://github.com/rubygems/rubygems/security/advisories/GHSA-fj7f-vq84-fh43—Reference removed https://www.sonarsource.com/blog/securing-developer-tools-package-managers/—Reference type removed https://github.com/rubygems/rubygems/commit/0fad1ccfe9dd7a3c5b82c1496df3c2b4842870d3 Types: Patch—Reference type removed https://github.com/rubygems/rubygems/commit/a4f2f8ac17e6ce81c689527a8b6f14381060d95f Types: Patch—Reference type removed https://github.com/rubygems/rubygems/pull/5142 Types: Patch—Reference type removed https://github.com/rubygems/rubygems/security/advisories/GHSA-fj7f-vq84-fh43 Types: Exploit, Vendor Advisory—Reference type removed https://www.sonarsource.com/blog/securing-developer-tools-package-managers/ Types: Exploit, Mitigation—Source identifier: security-advisories@github.com
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