# CVE-2026-100242: MediaWiki DataTransfer Extension uncontrolled resource consumption

Source: https://junglewise.ai/threats/cve-2026-100242-dependency-on-vulnerable-third-party-component-and-uncontrolled  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-29. Updated: 2026-09-29  
License: CC BY 4.0 with a link back

CVE-2026-100242 · Severity: info · Published 2026-09-29

The MediaWiki DataTransfer Extension relies on a vulnerable version of PHPSpreadsheet for spreadsheet file handling. A malformed XLS file can cause the extension to exhaust server memory and crash, denying service to users. Attackers can upload a tiny malicious spreadsheet file to trigger a denial-of-service condition affecting any MediaWiki installation using this extension.

Technologies: [Phpoffice Phpspreadsheet](https://junglewise.ai/threats/technologies/phpspreadsheet). Vendors: [Phpoffice](https://junglewise.ai/threats/vendors/phpoffice), [Wikimedia Foundation](https://junglewise.ai/threats/vendors/wikimedia-foundation).

## Quick answers

**Is CVE-2026-100242 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-100242 being exploited in the wild.

**How severe is CVE-2026-100242?** Informational severity, published 29 September 2026.

**Which products and versions are affected?** Phpoffice Phpspreadsheet <= 1.30.5, 2.0.0-2.1.17, 2.2.0-2.4.6, 3.3.0-3.10.6, 4.0.0-5.8.0; Wikimedia Foundation MediaWiki DataTransfer Extension 1.46.0 before 1.47.0.

**Is there a fix for CVE-2026-100242?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-100242 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-100242?** Check whether you run Phpoffice Phpspreadsheet or Wikimedia Foundation MediaWiki DataTransfer Extension at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The vulnerability stems from a dependency on PHPSpreadsheet versions with an unbounded sector-chain walk in OLE file parsing. The OLERead::read() function follows attacker-controlled sector chains without detecting cycles or enforcing maximum chain length, allowing a self-referencing sector pointer to cause infinite memory allocation. This flaw is reachable during file-type detection (canRead()) before format validation, making it exploitable via automatic spreadsheet upload handling.

## Affected products

- Wikimedia Foundation MediaWiki DataTransfer Extension 1.46.0 before 1.47.0
- PHPOffice PHPSpreadsheet <= 1.30.5, 2.0.0-2.1.17, 2.2.0-2.4.6, 3.3.0-3.10.6, 4.0.0-5.8.0

## Timeline

- 2026-09-29: disclosed

## References

- [https://gerrit.wikimedia.org/r/q/Ibc4a9070c2425b690bc767a882e4c35046a39be7](https://gerrit.wikimedia.org/r/q/Ibc4a9070c2425b690bc767a882e4c35046a39be7)

## Related threats

- [PHPOffice PhpSpreadsheet redirect validation bypass in external image loading](https://junglewise.ai/threats/cve-2026-108360-phpspreadsheet-is-a-pure-php-library-for-reading-and-writing)
- [PhpSpreadsheet denial-of-service via unbounded row repetition](https://junglewise.ai/threats/cve-2026-108359-phpspreadsheet-is-a-pure-php-library-for-reading-and-writing)
- [PhpSpreadsheet XmlScanner XML entity expansion denial of service](https://junglewise.ai/threats/cve-2026-108358-phpspreadsheet-is-a-pure-php-library-for-reading-and-writing)
- [PHPOffice PhpSpreadsheet XML entity expansion denial of service](https://junglewise.ai/threats/cve-2026-108357-phpspreadsheet-is-a-pure-php-library-for-reading-and-writing)
- [PHPOffice PhpSpreadsheet denial of service via Gnumeric gzip expansion](https://junglewise.ai/threats/cve-2026-59932-phpoffice-phpspreadsheet-denial-of-service-via-gnumeric-gzip)