*First ever post, so apologies for any associated naiveté* Scenario: The Windows Attachment Manager does not correctly handle JAR files marked as “high risk” when accessed via Internet Explorer 11. This leads to direct execution of any JAR file when a user clicks “Open” rather than “Save” or “Save as”, when the expected behaviour would be a nag dialog. Other files added to the same “high risk” category behave as expected, regardless of whether they are directly launched or first saved. Currently neither Chrome, Edge nor Firefox browsers provide an “Open” option for such files, and so are unaffected. With some social engineering this behaviour may be exploited to gain code execution at the privilege level of the affected user. This is most likely to be successful when the user has been conditioned to expect warnings from the Attachment Manager about potentially unsafe files. MS Security decided this wasn’t a security issue – and by their published definitions I accept that assertion. But sharing’s caring, this issue can and therefore probably will be abused, if it hasn’t already. To reproduce: Client OS – Windows 10 Pro (version 10.0.14393) Browser – IE11 (version 11.00.14393.0) *supplied with OS for backwards compatibility Sample Attachment Manager configuration Setting State Attribute : Value Trust logic for file attachments Enabled Determine risk by : Preferring the file handler Default risk level for file attachments Enabled Set the default risk level : High risk Inclusion list for high-risk file types Enabled .com;.bat;.exe;.pif;.scr;.msi;.ps1;.jar;.sh;.py;.Zip;.Rar;.7z;.gz;.tar;.vbs; .js;.wsf Inclusion list for low file types Enabled Inclusion list for moderate risk file types Enabled .doc;.xlsx;.docx; 1. Download any JAR file using the built-in IE11 (x64 or x86) and opt to open it. 2. The file opens without any nag dialog indicating the file type is potentially harmful. Hope it’s useful. Kind regards, Stevie
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