If you've ever built an application that processes user-uploaded images in Go, there's big news you shouldn't miss. Recently, a vulnerability tracked as CVE-2024-24792 was found in the Go standard library. If you parse a corrupt or intentionally crafted image with invalid color indices, your application might panic—causing a crash and potential denial of service.

In this exclusive read, we'll break down what this means, why it's dangerous, and how you can protect your own applications.

What Is CVE-2024-24792?

CVE-2024-24792 is a vulnerability in the Go language's image package. When parsing certain image file formats, like PNG, the decoding logic assumes all color palette indices inside the file are valid. But a malicious user could craft an image file with out-of-range color indices. When the Go code tries to use one of those invalid indices, it triggers a panic, which can crash your application.

Imagine a public server or web app that processes user images—this bug means a simple upload could knock it offline.

Why Is This Exploit Serious?

Panic in Go isn't a classic remote code execution, but it's often enough for a denial of service (DoS). A panic means the routine (unless handled with recover) will quit, and in most web servers, the request (or even the entire process) may die.

If your application doesn’t properly catch panics (hint: most don’t), this is a critical reliability bug. Attackers can use a single bad image to drop your service.

How Does the Exploit Work?

Let's see a simplified example. The Go package that reads PNG files parses the color index value for each pixel like this:

palette := []color.Color{ /* ... 16 colors ... */ }
index := img.PixelColorIndex(x, y)
c := palette[index] // <--- If 'index' is out of bounds, this panics!

If a user-uploaded image encodes an index bigger than the number of colors in the palette, this line will panic at runtime with panic: runtime error: index out of range.

Here's a minimal proof-of-concept to trigger the bug using a purposely corrupt PNG

package main

import (
	"bytes"
	"image/png"
	"os"
)

func main() {
	// Malicious PNG bytes (with invalid palette index)
	badPNG := []byte{
		// PNG header and data go here (craft with a bad index)
	}

	_, err := png.Decode(bytes.NewReader(badPNG))
	if err != nil {
		// Decoding error, but if it's a panic, the app may crash!
		println("Error decoding image:", err.Error())
	}
}

You'll need to generate a PNG with palette indices higher than the color table's size. This gist shows how to handcraft or fuzz corrupt PNGs.

Real-World Impact

If your Go server is exposed to image uploads or parsing (like thumbnails, avatars, or user content), you are at risk. Attackers can:

How Was It Fixed?

The Go team fixed this by checking palette boundaries before indexing. No more unchecked reads!

Patch details:
Go commit fixing CVE-2024-24792

If you use Go versions before Go 1.22.2 or Go 1.21.9, you are vulnerable.

References

- Go's Security Advisory: CVE-2024-24792
- NVD Summary
- Go’s Release Notes (1.22.2, 1.21.9)
- PNG Format reference for fuzz testing

return

}

Conclusion

The CVE-2024-24792 vulnerability shows that even mature libraries can have little pitfalls with big consequences. If your application handles images, it’s time to patch or protect. Otherwise, your users—or an attacker—could send one bad picture and crash your whole server!

Always keep your Go toolchain up to date, and remember: Trust no input—even if it just looks like a harmless image.


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Timeline

Published on: 06/27/2024 18:15:13 UTC
Last modified on: 08/01/2024 13:47:30 UTC