Vulnerability in bundler (CVE-2021-43809)

Summary

Vulnerability in bundler (CVE-2021-43809). Successful exploitation can lead to full system takeover. Exploitable via bundler. Mitigation: upgrade to 2.2.33 or later.

Original description

The description as published by the source.

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.

Exploitation

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 [u…

Source: OSV.dev (Open Source Vulnerabilities) NVD GitHub Advisory OSV

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2021-43809 has been found in bundler.
Attackers can target a specific entry point like bundler over the network to misuse the product.
Successful exploitation can lead to full system takeover.
What to do: upgrade bundler to 2.2.33 or later.
If unsure, ask your IT team or search "bundler CVE-2021-43809" on the vendor's site.

CVE-2021-43809 (bundler) — CWE-88
Attack vector: local
Attack surface: bundler / Gemfile / gem / git
Patched: 2.2.33 — apply immediately
Workaround: 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.
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

A vulnerability (CWE-88) exists in bundler. Attackers reach the vulnerable code path via bundler.

📍 Affected scope

Check the vendor advisory for the affected versions of bundler. Attack surface: bundler / Gemfile / gem / git.

🔥 Severity

Severity: ?. Successful exploitation can lead to full system takeover.

🔧 How to fix

Update to 2.2.33.

🛡️ Workaround

Workaround: 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.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'bundler' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

1
Identify exposure identify
```
grep -r 'bundler' . | grep -v node_modules
```
リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で bundler を grep し、稼働しているサービス・バージョンを把握する。
2
Apply temporary workaround mitigate
```
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.
```
パッチが適用されるまでの応急処置として、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. を実施。回避策の副作用 (機能低下) を確認した上で。
3
Apply patch patch
```
Upgrade bundler to 2.2.33
```
ステージング環境で 2.2.33 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
4
Post-deployment verification verify
```
Confirm patched version is live in production
```
パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

RubyGems bundler

[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.2.33"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

Alpine Linux ALPINE-CVE-2021-43809 ruby-bundler Fixed in: 2.2.33-r0
Debian DEBIAN-CVE-2021-43809 rubygems Fixed in: 3.3.5-1