● CVE-2024-27983 / High Severity

CVE-2024-27983: Node.js llhttp HTTP Request Smuggling Teardown

How incomplete Transfer-Encoding chunk extension parsing in deps/llhttp caused HTTP request desynchronization, enabling cache poisoning and credential theft.

💡 身近な例えで分かる解説 (ELI5)

Imagine a two-window ticket booth. Window 1 reads: 'One ticket for Alice'. Window 2 reads: 'Wait, there's another ticket for Bob glued to the back'. Because Window 1 ignored the extra ticket, Bob's ticket sits in the window until Charlie walks up. Charlie gets handed Bob's ticket and private receipt, allowing an attacker to steal user sessions.

中核となる概念とサブシステム用語

llhttp
The high-performance C HTTP parser library embedded inside Node.js to parse incoming HTTP/1.1 requests.
HTTP Request Smuggling
Desynchronization between frontend reverse proxies (e.g. NGINX, Cloudflare) and backend Node.js servers regarding request boundaries.
Chunked Transfer-Encoding
An HTTP streaming mechanism where payloads are sent in numbered chunks, terminated by a `0\r\n\r\n` chunk.
Chunk Extensions
Optional semicolon-delimited parameters appended to the chunk length (`0;extension=value\r\n`).

ステップ別エクスプロイト実行メカニズム

Step 1

1. Send Ambiguous Request

The attacker sends an HTTP request with chunk extensions containing unescaped control characters.

Step 2

2. Frontend Interpretation

The frontend proxy treats the entire payload as a single continuous request body.

Step 3

3. Node.js Parser Desync

Node.js's llhttp stops parsing prematurely, leaving the smuggled second request in the TCP buffer.

Step 4

4. Victim Session Hijacking

The next innocent user's request is prepended to the smuggled request, exfiltrating their session tokens.

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: deps/llhttp/src/llhttp.c before patch
int llhttp__on_chunk_extension(llhttp_t *parser, const char *p, const char *end) {
    // ROOT CAUSE:
    // Does not enforce strict ASCII validation on chunk extension tokens!
    // Tolerates invalid whitespace and carriage return sequences, desyncing from proxies!
    while (p < end && *p != '\r' && *p != '\n') {
        p++; // Skips unvetted extension bytes
    }
    return 0;
}
修正済みの安全なコード
// SECURE: deps/llhttp/src/llhttp.c patch
int llhttp__on_chunk_extension(llhttp_t *parser, const char *p, const char *end) {
    // 1. Strictly validate characters inside chunk extensions according to RFC 9112
    while (p < end && *p != '\r' && *p != '\n') {
        uint8_t ch = (uint8_t)*p;
        // Disallow spaces, control codes, and invalid token bytes
        if (ch <= 0x20 || ch >= 0x7F || ch == ';') {
            return HPE_INVALID_CHUNK_SIZE; // Reject immediately!
        }
        p++;
    }
    return 0;
}

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