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High, CVSS 8.8amended

PhpSpreadsheet: XmlScanner Bypass via Double-Encoded unentity() TOCTOU Allows XXE and Denial of Service

CVE-2026-108357GHSA-rxj4-h86g-25gc

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (phpoffice/phpspreadsheet 5.10.0, 3.10.8), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
8.8 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:H/SC:L/SI:N/SA:N · score source
EPSS
  • CVE-2026-108357: 0.46% estimated exploitation activity in the next 30 days; percentile 40.19 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Summary The SpreadsheetML XML reader (`Reader\Xml`) scans file content twice through `XmlScanner::scan()`, and each scan runs an `unentity()` callback that calls `html_entity_decode()` after the pattern check. By double-encoding the ` toUtf8($xml); if (preg_match($pattern, $xml)) { // CHECK 2 (UTF-8) throw new Exception('Detected use of ENTITY...'); } if ($this->callback !== null) { $xml = call_user_func($this->callback, $xml); // DECODE (after checks!) } return $xml; // getSecurityScannerOrThrow()->scan($data); // 1st scan // ... $this->fileContents = $data; // stores partially-decoded content ``` 3. `Xml::trySimpleXMLLoadStringPrivate()` (Xml.php, lines 120–150) — re-scans the stored content: ```php $data = $this->fileContents; // already partially decoded $xml = simplexml_load_string( $this->getSecurityScannerOrThrow()->scan($data) // 2nd scan finishes decoding ); ``` The double-scan decode chain: ``` Raw file: <!DOCTYPE | 1st scan(): pattern check → no…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Amended from osv record GHSA-rxj4-h86g-25gc

  2. Revision 1 · created ·

    Published from ghsa record GHSA-rxj4-h86g-25gc

Agent brief

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# Patch Next advisory brief: CVE-2026-108357

Advisory: PhpSpreadsheet: XmlScanner Bypass via Double-Encoded unentity() TOCTOU Allows XXE and Denial of Service
IDs: CVE-2026-108357, GHSA-rxj4-h86g-25gc
Record: https://patchnext.com/advisories/cve-2026-108357 (revision 2, source checked 28 Oct 2026, 06:30 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: phpoffice/phpspreadsheet 5.10.0, 3.10.8. A vendor fix does not mean a deployment is fixed.

## Affected components
- Packagist phpoffice/phpspreadsheet: affected >= 4.0.0, < 5.10.0; >= 3.3.0, < 3.10.8; fixed in 3.10.8, 5.10.0

## Suggested inspection (read-only)
- Packagist phpoffice/phpspreadsheet: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on phpoffice/phpspreadsheet.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-rxj4-h86g-25gc (GitHub-reviewed advisory GHSA-rxj4-h86g-25gc lists affected ranges: Packagist phpoffice/phpspreadsheet >=4.0.0 =3.3.0 <=3.10.7)
- Verified: https://osv.dev/vulnerability/GHSA-rxj4-h86g-25gc (OSV record GHSA-rxj4-h86g-25gc lists affected ranges: Packagist phpoffice/phpspreadsheet >=4.0.0 =3.3.0 <3.10.8 (fixed))

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