GitHub Security Advisory: GHSA-r9x7-7ggj-fx9f
Package: privatebin/privatebin (COMPOSER)
Severity: LOW (CVSS 3.9)
CWE: CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Vulnerable versions: >= 1.7.7, < 2.0.3
Patched in: 2.0.3

Summary: PrivateBin vulnerable to malicious filename use for self-XSS / HTML injection locally for users

Details:
## Summary

Dragging a file whose filename contains HTML is reflected verbatim into the page via the drag-and-drop helper, so any user who drops a crafted file on PrivateBin will execute arbitrary JavaScript within their own session (self-XSS). This allows an attacker who can entice a victim to drag or otherwise attach such a file to exfiltrate plaintext, encryption keys, or stored pastes before they are encrypted or sent.

**Note 1:** as the malicious filename must contain the `>` character, the victim must not be using Windows for this to work, since this OS simply forbids this character in filenames.

**Note 2:** most PrivateBin instances use the Content-Security-Policy header to prevent most use-cases of this vulnerability. This report will describe the impact as if this header had been disabled by the PrivateBin instance owner.

## Affected versions

PrivateBin versions since 1.7.7 and before 2.0.3.

## Conditions

* Only macIOS or Linux users are affected, due to the way the `>` character is treated in a file name on Windows.
* The PrivateBIn instance needs to have file upload enabled.
* An attacker needs to have access to the local file system or somehow convince the user to create (or download) a malicious file (name).
* An attacker needs to convince the user to attach that malicious file to PrivateBin.

## Impact

Any Mac / Linux user who can be tricked into dragging a maliciously named file into the editor is impacted; code runs in the origin of the PrivateBin instance they are using. Attackers can steal plaintext, passphrases, or manipulate the UI before data is encrypted, defeating the zero-knowledge guarantees for that victim session, assuming counter-measures like Content-Security-Policy (CSP) have been disabled.

If CSP is not disabled, similar HTML injection attacks as described in CVE-2025-62796 may be possible - like redirecting to a foreign website, phishing etc.

### Real-life impact

As the whole exploit needs to be included in the file name of the attached file and only affects the local session of the user (aka it is neither persistent nor remotely executable) _and_ that user needs to interact and actively attach that file to the paste, the impact is considered to be practically low.

## Technical Description

When a file is dropped, `readFileData` collects all filenames and calls `printDragAndDropFileNames`:

```js
const fileNames = loadedFiles.map((loadedFile => loadedFile.name));
printDragAndDropFileNames(fileNames);
```

`printDragAndDropFileNames` then renders those names:

```js
        function printDragAndDropFileNames(fileNames) {
            $dragAndDropFileNames.html(fileNames.join('<br>'));
        }
```

This will insecurely render the user-submitted filenames as HTML.

This vulnerability has been introduced in [this commit](https://github.com/PrivateBin/PrivateBin/commit/095a5be0b6390a6e47b97d3668a23f6edec95c15) (introduced in 1.7.7).

The previous render method was using `.text()`:

```js
$dragAndDropFileName