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Sanitize download attribute file names in DownloadingAttachmentHandler - #1184
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rbri merged 1 commit intoNov 2, 2026
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The file name of a download started by an anchor with a download attribute is passed to the AttachmentHandler as it is; only names from the Content-Disposition header are sanitized. DownloadingAttachmentHandler resolved this name against the download folder, so a page could use download="../x" or an absolute path to create a file anywhere outside of it. Sanitize the name the same way as the header name before resolving it.
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great - thanks |
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Thanks for merging this, glad it went in cleanly. |
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Repro: set
webClient.setAttachmentHandler(new DownloadingAttachmentHandler(dir))and load a page whose script doesa.download = '../evil.txt'; a.click();, or sets an absolute path such as/home/user/.config/autostart/x.desktop. The response of the link is written to the path the page chose, outside ofdir, and nothing is saved indir. Only new files are created (an existing name gets the(1)suffix), but anywhere the JVM user can write.Cause: for a
downloadattribute,WebClient.loadWebResponseInto()passes the attribute value to theAttachmentHandlerunchanged; only names from the Content-Disposition header go throughAttachment.getSuggestedFilename().DownloadingAttachmentHandler.determineDestionationFile()then callsdownloadFolder_.resolve(fileName), which follows..and returns an absolute name as it is.Fix: run the name through the existing
Attachment.sanitizeFilename()(now package private) inDownloadingAttachmentHandlerbefore resolving it.../../evil.txtbecomes_.._evil.txt, the name the header path already produces (AttachmentSuggestedFilename2Test.pathTraversal); browsers do not let the download attribute pick a directory either. Doing it in the handler covers every source of the name, not only the anchor.DownloadingAttachmentHandlerTest.fileNameFromDownloadAttributeIsSanitizedcovers a relative and an absolute name and fails without the change. The attachment, anchor and area tests andCodeStyleTestpass.