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Fix GH-20631: Integer underflow in exif HEIF parsing

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When pos.size is less than 2, the subtraction pos.size - 2 causes
an unsigned integer underflow, resulting in a ~4GB allocation attempt.

Add minimum size check (pos.size >= 2) to prevent the underflow.

Closes GH-20630.
This commit is contained in:
Oblivionsage
2025-12-02 18:57:05 +01:00
committed by Niels Dossche
parent aa82371358
commit 6a0da6dc2e
3 changed files with 23 additions and 1 deletions
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3
NEWS
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@@ -2,6 +2,9 @@ PHP NEWS
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
?? ??? ????, PHP 8.5.2
- EXIF:
. Fixed bug GH-20631 (Integer underflow in exif HEIF parsing
when pos.size < 2). (Oblivionsage)
18 Dec 2025, PHP 8.5.1

2
ext/exif/exif.c
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@@ -4421,7 +4421,7 @@ static bool exif_scan_HEIF_header(image_info_type *ImageInfo, unsigned char *buf
if (exif_read_from_stream_file_looped(ImageInfo->infile, (char*)(data + remain), limit - remain) == limit - remain) {
exif_isobmff_parse_meta(data, data + limit, &pos);
}
if ((pos.size) &&
if ((pos.size >= 2) &&
(pos.size < ImageInfo->FileSize) &&
(ImageInfo->FileSize - pos.size >= pos.offset) &&
(php_stream_seek(ImageInfo->infile, pos.offset + 2, SEEK_SET) >= 0)) {

19
ext/exif/tests/heic_iloc_underflow.phpt Normal file
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@@ -0,0 +1,19 @@
--TEST--
HEIC iloc extent_length underflow
--EXTENSIONS--
exif
--FILE--
<?php
// Read valid HEIC file and patch iloc extent_length to 1
$data = file_get_contents(__DIR__."/image029.heic");
$data = substr_replace($data, "\x00\x00\x00\x01", 0x4f8, 4);
file_put_contents(__DIR__."/heic_iloc_underflow.heic", $data);
var_dump(exif_read_data(__DIR__."/heic_iloc_underflow.heic"));
?>
--CLEAN--
<?php
@unlink(__DIR__."/heic_iloc_underflow.heic");
?>
--EXPECTF--
Warning: exif_read_data(heic_iloc_underflow.heic): Invalid HEIF file in %s on line %d
bool(false)