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