Description

PrivateBin is an online pastebin where the server has zero knowledge of pasted data. Prior to 2.0.5, AttachmentViewer.setAttachment in js/privatebin.js uses getAttachmentMimeType to accept attacker-controlled MIME types and uses getBlobUrl to create a same-origin blob before setting attachmentLink's href for the Download attachment link. The SVG-only sanitization branch updates only the preview blob, so text/html, image/svg, application/xhtml+xml, and text/xml attachments can remain active in the download blob. On an instance with fileupload = true and a weakened, stripped, or absent Content Security Policy, an anonymous attacker can create such an attachment, and a victim who opens the link in a new tab causes inline JavaScript to execute in the PrivateBin origin. The script can read origin-scoped local storage and issue same-origin requests, including requests to applications co-hosted on the same domain. This issue is fixed in version 2.0.5.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "4.3",
  "pubDate": "2026-08-28T22:16:51.553Z",
  "pubdate": "2026-08-28T22:16:51.553Z",
  "executiveSummary": "PrivateBin versions prior to 2.0.5 are susceptible to a stored Cross-Site Scripting (XSS) vulnerability residing in the attachment handling logic.\nThe vulnerability occurs because the application fails to properly sanitize MIME types for attachments, allowing attackers to upload malicious files such as HTML or SVG content that execute JavaScript within the PrivateBin origin.\nSuccessful exploitation permits an unauthenticated attacker to execute arbitrary scripts in the victim's browser session. The impact includes unauthorized access to origin-scoped local storage and the ability to perform authenticated requests on behalf of the victim, potentially impacting other applications co-hosted on the same domain.\nThe vulnerability is contingent upon the instance configuration having fileupload enabled and a weakened, stripped, or absent Content Security Policy (CSP).\nThis represents a significant security risk for PrivateBin instances, as it effectively bypasses the application's client-side security model by delivering malicious payloads through the attachment download mechanism.",
  "technicalDetails": "The root cause of this vulnerability lies in the improper handling of attachment MIME types within the AttachmentViewer.setAttachment function located in js/privatebin.js.\nSpecifically, the application utilizes getAttachmentMimeType to determine the attachment type and subsequently employs getBlobUrl to generate a same-origin blob for the 'Download attachment' link.\nWhile the application implemented a sanitization branch for SVG files, it failed to extend this security control to other dangerous MIME types, including text/html, image/svg, application/xhtml+xml, and text/xml.\nWhen a user interacts with a malicious attachment, the browser interprets the blob URL in the context of the PrivateBin origin. If the server-side CSP is improperly configured or absent, the browser does not restrict the execution of embedded JavaScript within these malicious blobs.\nThe attack flow proceeds as follows: First, an anonymous attacker crafts an attachment containing malicious inline JavaScript, specifying a dangerous MIME type (e.g., text/html). Second, the attacker uploads this file to a PrivateBin instance where fileupload is enabled. Third, the attacker distributes the generated attachment link to a victim. Fourth, upon the victim opening the link in a new tab, the browser renders the content as a same-origin resource. Finally, the malicious script executes within the PrivateBin origin context, inheriting the victim's session privileges.\nPost-exploitation impact includes the ability for the attacker to exfiltrate data from local storage, perform same-origin HTTP requests, and compromise other services co-hosted on the same domain that rely on the same origin for trust.\nThe vulnerability affects all versions of PrivateBin prior to 2.0.5. It does not require authentication or elevated privileges, as it is designed for anonymous interaction within the pastebin framework. The exploit is entirely network-accessible if the instance is exposed to the public."
}