Apple ImageIO Zero-Day – Actively Exploited via Malicious Image Files CVE-2025-43300

1) TL;DR

• Bug class: Out-of-bounds write in ImageIO while parsing a crafted image.

• What a red team cares about: Turn the OOB-write into a reliable primitive (heap corruption → control of flow), delivered through common image parsing paths (messaging previews, mail, web).

• What a blue team watches: ImageIO-related crashes, abnormal previewing, suspicious image fingerprints, rapid patch verification.

• No PoC here: We explain the mechanics, not the exact trigger or bytes.

2) Attack Surface (Why images are powerful)

Modern OSes invoke ImageIO (or equivalent codecs) in many places you don’t explicitly “open” an image: thumbnailers, link previews, message notifications, Mail, and browsers. If a decoder mis-calculates a buffer size or trusts a metadata field (dimensions, color planes, ICC profiles, EXIF blocks, chunk lengths), a crafted file can push the parser into writing past a buffer boundary.

Typical surface (non-exhaustive):

• Message previews (zero-click risk if a preview auto-parses).

• Email clients showing inline images.

• Web content with <img> or CSS images.

• Files app / Finder thumbnail generation.

3) Exploitation Logic (Conceptual, PoC-free)

3.1 From metadata to memory corruption

A classic path looks like this (illustrative pseudo-flow):

1. Parser reads header/metadata → trusts fields like width, height, channels, or chunk length from the file.

2. Calculates buffer sizes → e.g., row_bytes = width * bpp + padding.

3. Allocates a buffer based on those calculations.

4. Copies/decodes pixel or metadata payload into the target buffer.

5. Bug: if the calculation overflows (32-bit multiply) or a chunk length is not re-validated, the copy/write exceeds the allocated region → out-of-bounds write.

3.2 Unsafe vs. safer patterns (illustrative, not ImageIO code)

Unsafe (conceptual C-like pseudo):

// Danger: 32-bit math & no bounds checks
uint32_t row = hdr.width * hdr.bytes_per_pixel;  // may overflow
uint32_t total = row * hdr.height;               // may overflow again
uint8_t *buf = (uint8_t*)malloc(total);
memcpy(buf, payload, total);                     // trusts file-controlled 'total'

Safer approach (conceptual):

// Use 64-bit, check ceilings, re-validate chunk lengths vs. actual payload
bool safe_mul_u64(uint64_t a, uint64_t b, uint64_t limit, uint64_t *out) {
    __uint128_t t = (__uint128_t)a * b;
    if (t > limit) return false;
    *out = (uint64_t)t;
    return true;
}

bool decode(const Header hdr, const uint8_t* payload, size_t payload_len) {
    uint64_t row=0, total=0;
    if (!safe_mul_u64(hdr.width, hdr.bytes_per_pixel, UINT64_C(1)<<40, &row)) return false;
    if (!safe_mul_u64(row, hdr.height, UINT64_C(1)<<40, &total)) return false;
    if (total > payload_len) return false; // length re-check

    uint8_t *buf = (uint8_t*)malloc((size_t)total);
    if (!buf) return false;
    memcpy(buf, payload, (size_t)total);
    return true;
}

5. From Crash to Code Execution

• Heap Shaping: Red-team tries to influence allocation patterns so the OOB write lands on useful objects.

• Determinism: Reliable corruption requires predictable layout.

• Hijack: If the overwritten object holds a pointer (vtable, function pointer, allocator metadata), execution flow may be redirected.

• Bypasses: Modern iOS/macOS defenses (ASLR, PAC, hardened malloc) require chaining with info-leak bugs or using single-shot corruption.

6. Delivery Vectors

• Zero-click: auto-parsing previews (e.g., iMessage, Mail).

• Social engineering: convincing the user to open/view a crafted image.

• Web injection: hosting the malicious image on a site or ad network.

7. Blue-Team Telemetry

• Crash Logs: ImageIO-related crashes in Diagnostic Logs.

• Anomaly Detection: unusual large or malformed EXIF/ICC metadata.

• Hash/Signature: repeated suspicious image files across multiple endpoints.

• Process Behavior: abnormal memory access by apps invoking ImageIO.

Example safe YARA heuristic (metadata-based, not exploit-based):

rule Suspicious_Large_Metadata
{
  meta:
    description = "Images with oversized EXIF/ICC blocks (potential exploit carriers)"
  strings:
    $exif = "Exif" ascii
    $icc  = "ICC_PROFILE" ascii
  condition:
    filesize > 5MB and ( $exif or $icc )
}

8. Mitigation Checklist

• Patch immediately: iOS 18.6.2, iPadOS 17.7.10, macOS Sequoia 15.6.1 / Sonoma 14.7.8 / Ventura 13.7.8.

• Restrict previews: in enterprise configs, disable auto-preview where possible.

• Content filtering: flag oversized/unusual metadata in inbound images.

• MDM/EDR rules: log and alert on repeated parsing failures or crashes in ImageIO.

9. Conclusion

For red-teamers, CVE-2025-43300 is a case study in how trivial-looking parsing bugs escalate into high-value attack chains. For defenders, it’s a reminder that innocent-looking content (images) can be weaponized at scale.

👉 Always patch promptly, monitor aggressively, and treat media parsers as a high-risk attack surface.