A serious vulnerability has been discovered in the SkBmpStandardCodec component of Skia, a widely used 2D graphics library found in browsers like Google Chrome, Chromium-based products, and many Android apps. This flaw, identified as CVE-2025-26416, is triggered in the initializeSwizzler function of SkBmpStandardCodec.cpp, allowing a remote attacker to achieve out-of-bounds write via a heap buffer overflow.

In this in-depth article, we’ll explain how the vulnerability works, provide actual code snippets, review the real-world impact, explore possible exploits, and share links to official advisories for further reading.

What is Skia and SkBmpStandardCodec?

Skia is an open-source 2D graphics engine. The SkBmpStandardCodec.cpp file handles the decoding of BMP images. The function initializeSwizzler sets up routines for converting pixel formats.

Vulnerability Overview

The bug arises because initializeSwizzler fails to validate the size of incoming BMP image data against buffer boundaries. If an attacker supplies a crafted BMP file with properties leading the codec to underestimate buffer requirements, the subsequent copy operations can write beyond the allocated memory.

Code Snippet: Vulnerable Implementation

Here’s a simplified version highlighting the problematic segment. (Note: Actual Skia code is more complex, this is for clarity.)

bool SkBmpStandardCodec::initializeSwizzler(int width, int height) {
    // Allocate buffer based on width x height
    uint8_t* pixels = new uint8_t[width * height * bytesPerPixel];
    // ... some setup ...

    // Copy image data from source buffer
    memcpy(pixels, srcBuffer, width * height * bytesPerPixel); // <-- Potential overflow!
    // ...
}

What’s wrong?
There’s no check that width * height * bytesPerPixel fits inside the actual allocated buffer or matches srcBuffer length. A crafted BMP can set these fields to large or malicious values.

How Can This Be Exploited?

A remote attacker can exploit this bug by sending or embedding a specially crafted BMP file (via a website, email, or app data). As soon as the vulnerable library decodes the image:

Attacker gains the ability to overwrite adjacent memory.

- With careful design, this leads to arbitrary code execution under the context of the process decoding the BMP (such as a browser or app).

No action is needed by the user except viewing, downloading, or opening the data in an affected product.

Proof-of-Concept (PoC) Outline

Below is a basic illustration—not an actual exploit—but it demonstrates how an attacker might trigger the bug:

1. Craft a malicious BMP file with headers indicating huge width/height.

Send or host the image so that a vulnerable app loads it.

3. Observe crash or control: App crashes (DoS) or, if attacker controls overwritten memory, executes malicious code.

Sketch of a Malicious BMP Header

# In Python - writes a BMP with oversized width/height fields
with open("evil.bmp", "wb") as f:
    f.write(b'BM')                    # Signature
    f.write(b'\x36\x00\x00\x00')      # File size
    f.write(b'\x00\x00')              # Reserved
    f.write(b'\x00\x00')              # Reserved
    f.write(b'\x36\x00\x00\x00')      # Offset to data
    f.write(b'\x28\x00\x00\x00')      # Header size
    f.write(b'\xff\xff\x00\x00')      # width = 65535
    f.write(b'\xff\xff\x00\x00')      # height = 65535
    # ... fill in rest, minimal BMP

Impact

- Remote Code Execution: Exploiter could run code as the vulnerable process (e.g., browser process, Android app, etc.)
- Privilege Escalation: Because many apps run with high or sensitive privileges, this may lead to full system compromise.

Check for Official Patches:

- Skia GitHub Issues
- Chromium Security Advisories
- Android Security Bulletins

If you can’t update immediately:

References

- Skia Bug Report for CVE-2025-26416 (if/when public)
- NVD Entry for CVE-2025-26416
- Chromium Security Advisories
- Skia Open-Source GitHub

Conclusion

CVE-2025-26416 is a clear example of how a small unchecked calculation can lead to significant security threats. If you maintain systems or software that use Skia, update your dependencies as soon as possible.
If you’re a user, make sure browsers and apps are up-to-date, and be careful with files from untrusted sources.

Timeline

Published on: 09/02/2025 23:15:35 UTC
Last modified on: 09/04/2025 16:37:27 UTC