CVE-2026-54134

OctoPrint provides a web interface for controlling consumer 3D printers. Prior to 1.11.8 and 2.0.0rc3, OctoPrint's custom Tornado upload handler and Flask with Werkzeug parse request parameters differently, allowing an attacker with FILE_UPLOAD permission to inject reserved internal upload fields through query parameters or parser differentials despite the earlier GHSA-m9jh-jf9h-x3h2 fix. The affected endpoints are /api/files/{local|sdcard}, /api/languages, /plugin/backup/restore, and /plugin/pluginmanager/upload_file. An attacker can make OctoPrint treat an arbitrary host file as a temporary upload, move it into a downloadable upload directory, disclose configuration secrets or other readable files, and remove runtime files in a way that can affect a later restart. This issue is fixed in versions 1.11.8 and 2.0.0rc3.

OctoPrint provides a web interface for controlling consumer 3D printers. Prior to 1.11.8 and 2.0.0rc3, OctoPrint's custom Tornado upload handler and Flask with Werkzeug parse request parameters differently, allowing an attacker with FILE_UPLOAD permission to inject reserved internal upload fields through query parameters or parser differentials despite the earlier GHSA-m9jh-jf9h-x3h2 fix. The affected endpoints are /api/files/{local|sdcard}, /api/languages, /plugin/backup/restore, and /plugin/pluginmanager/upload_file. An attacker can make OctoPrint treat an arbitrary host file as a temporary upload, move it into a downloadable upload directory, disclose configuration secrets or other readable files, and remove runtime files in a way that can affect a later restart. This issue is fixed in versions 1.11.8 and 2.0.0rc3.

Impact

OctoPrint versions up until and including 1.11.7 as well as 2.0.0rc1 and 2.0.0rc2 contain a vulnerability that allows an attacker with the FILE_UPLOAD permission to exfiltrate files from the host that OctoPrint has read access to, by moving them into the upload folder where they then can be downloaded from. This vulnerability was already reported as GHSA-m9jh-jf9h-x3h2/CVE-2025-48067 but the fix provided in OctoPrint 1.11.2 turned out to be incomplete.

The primary risk lies in the potential exfiltration of secrets stored inside OctoPrint's config, or further system files. By removing important runtime files, this could also be used to impact the availability of the host after an attempted server restart. Given that the attacker requires a user account with file upload permissions, the actual impact of this should however hopefully be minimal in most cases.

Patches

The vulnerability has been patched in version 1.11.8 and 2.0.0rc3.

Details

OctoPrint's web application is implemented in Flask, but uploads are first intercepted by a custom upload handler built on Tornado that sits in front of it. The handler streams the upload to a temporary file on disk - so files larger than the available memory can be uploaded - and rewrites the request, adding internal form fields that tell Flask where to find that temporary file.

These fields are reserved and meant to be set only by the upload handler, never by the client. The previous fix from GHSA-m9jh-jf9h-x3h2/CVE-2025-48067 stripped them from the request received from the client when they were sent as multipart form fields, yet they could still reach Flask through other channels: as plain query parameters, or - since the Tornado handler and Flask did not parse requests identically - smuggled in via several "parser differentials" that looked harmless to the handler while Flask still saw the injected fields. Any of these let an attacker make OctoPrint treat an arbitrary file on the host as a freshly uploaded one and move it into the upload folder.

The following endpoints in OctoPrint are affected:

• /api/files/{local|sdcard}
• /api/languages
• /plugin/backup/restore
• /plugin/pluginmanager/upload_file

Further upload endpoints in third party plugins might be affected too.

The fix rejects requests carrying any of the reserved fields, aligns the Tornado handler's request parsing with Flask's (Werkzeug) to avoid any differential parsing, and re-validates the request rewritten by Tornado before forwarding it to Flask.

Credits

This vulnerability was discovered and responsibly disclosed to OctoPrint by Koh Jun Sheng and Jacopo Tediosi.

Timeline

2026-06-04: Report received 2026-06-04: Report acknowledged 2026-06-08: Report verified 2026-06-17: Fix ready for 1.11.x 2026-06-22: Fix ported to 2.0.0 2026-06-23: Fix released with 1.11.8 and 2.0.0rc3

OctoPrint provides a web interface for controlling consumer 3D printers. Prior to 1.11.8 and 2.0.0rc3, OctoPrint's custom Tornado upload handler and Flask with Werkzeug parse request parameters differently, allowing an attacker with FILE_UPLOAD permission to inject reserved internal upload fields through query parameters or parser differentials despite the earlier GHSA-m9jh-jf9h-x3h2 fix. The affected endpoints are /api/files/{local|sdcard}, /api/languages, /plugin/backup/restore, and /plugin/pluginmanager/upload_file. An attacker can make OctoPrint treat an arbitrary host file as a temporary upload, move it into a downloadable upload directory, disclose configuration secrets or other readable files, and remove runtime files in a way that can affect a later restart. This issue is fixed in versions 1.11.8 and 2.0.0rc3.

OctoPrint provides a web interface for controlling consumer 3D printers. Prior to 1.11.8 and 2.0.0rc3, OctoPrint's custom Tornado upload handler and Flask with Werkzeug parse request parameters differently, allowing an attacker with FILE_UPLOAD permission to inject reserved internal upload fields through query parameters or parser differentials despite the earlier GHSA-m9jh-jf9h-x3h2 fix. The affected endpoints are /api/files/{local|sdcard}, /api/languages, /plugin/backup/restore, and /plugin/pluginmanager/upload_file. An attacker can make OctoPrint treat an arbitrary host file as a temporary upload, move it into a downloadable upload directory, disclose configuration secrets or other readable files, and remove runtime files in a way that can affect a later restart. This issue is fixed in versions 1.11.8 and 2.0.0rc3.

Impact

OctoPrint versions up until and including 1.11.7 as well as 2.0.0rc1 and 2.0.0rc2 contain a vulnerability that allows an attacker with the FILE_UPLOAD permission to exfiltrate files from the host that OctoPrint has read access to, by moving them into the upload folder where they then can be downloaded from. This vulnerability was already reported as GHSA-m9jh-jf9h-x3h2/CVE-2025-48067 but the fix provided in OctoPrint 1.11.2 turned out to be incomplete.

The primary risk lies in the potential exfiltration of secrets stored inside OctoPrint's config, or further system files. By removing important runtime files, this could also be used to impact the availability of the host after an attempted server restart. Given that the attacker requires a user account with file upload permissions, the actual impact of this should however hopefully be minimal in most cases.

Patches

The vulnerability has been patched in version 1.11.8 and 2.0.0rc3.

Details

OctoPrint's web application is implemented in Flask, but uploads are first intercepted by a custom upload handler built on Tornado that sits in front of it. The handler streams the upload to a temporary file on disk - so files larger than the available memory can be uploaded - and rewrites the request, adding internal form fields that tell Flask where to find that temporary file.

These fields are reserved and meant to be set only by the upload handler, never by the client. The previous fix from GHSA-m9jh-jf9h-x3h2/CVE-2025-48067 stripped them from the request received from the client when they were sent as multipart form fields, yet they could still reach Flask through other channels: as plain query parameters, or - since the Tornado handler and Flask did not parse requests identically - smuggled in via several "parser differentials" that looked harmless to the handler while Flask still saw the injected fields. Any of these let an attacker make OctoPrint treat an arbitrary file on the host as a freshly uploaded one and move it into the upload folder.

The following endpoints in OctoPrint are affected:

• /api/files/{local|sdcard}
• /api/languages
• /plugin/backup/restore
• /plugin/pluginmanager/upload_file

Further upload endpoints in third party plugins might be affected too.

The fix rejects requests carrying any of the reserved fields, aligns the Tornado handler's request parsing with Flask's (Werkzeug) to avoid any differential parsing, and re-validates the request rewritten by Tornado before forwarding it to Flask.

Credits

This vulnerability was discovered and responsibly disclosed to OctoPrint by Koh Jun Sheng and Jacopo Tediosi.

Timeline

2026-06-04: Report received 2026-06-04: Report acknowledged 2026-06-08: Report verified 2026-06-17: Fix ready for 1.11.x 2026-06-22: Fix ported to 2.0.0 2026-06-23: Fix released with 1.11.8 and 2.0.0rc3

Impact

OctoPrint versions up until and including 1.11.7 as well as 2.0.0rc1 and 2.0.0rc2 contain a vulnerability that allows an attacker with the FILE_UPLOAD permission to exfiltrate files from the host that OctoPrint has read access to, by moving them into the upload folder where they then can be downloaded from. This vulnerability was already reported as GHSA-m9jh-jf9h-x3h2/CVE-2025-48067 but the fix provided in OctoPrint 1.11.2 turned out to be incomplete.

The primary risk lies in the potential exfiltration of secrets stored inside OctoPrint's config, or further system files. By removing important runtime files, this could also be used to impact the availability of the host after an attempted server restart. Given that the attacker requires a user account with file upload permissions, the actual impact of this should however hopefully be minimal in most cases.

Patches

The vulnerability has been patched in version 1.11.8 and 2.0.0rc3.

Details

OctoPrint's web application is implemented in Flask, but uploads are first intercepted by a custom upload handler built on Tornado that sits in front of it. The handler streams the upload to a temporary file on disk - so files larger than the available memory can be uploaded - and rewrites the request, adding internal form fields that tell Flask where to find that temporary file.

These fields are reserved and meant to be set only by the upload handler, never by the client. The previous fix from GHSA-m9jh-jf9h-x3h2/CVE-2025-48067 stripped them from the request received from the client when they were sent as multipart form fields, yet they could still reach Flask through other channels: as plain query parameters, or - since the Tornado handler and Flask did not parse requests identically - smuggled in via several "parser differentials" that looked harmless to the handler while Flask still saw the injected fields. Any of these let an attacker make OctoPrint treat an arbitrary file on the host as a freshly uploaded one and move it into the upload folder.

The following endpoints in OctoPrint are affected:

• /api/files/{local|sdcard}
• /api/languages
• /plugin/backup/restore
• /plugin/pluginmanager/upload_file

Further upload endpoints in third party plugins might be affected too.

The fix rejects requests carrying any of the reserved fields, aligns the Tornado handler's request parsing with Flask's (Werkzeug) to avoid any differential parsing, and re-validates the request rewritten by Tornado before forwarding it to Flask.

Credits

This vulnerability was discovered and responsibly disclosed to OctoPrint by Koh Jun Sheng and Jacopo Tediosi.

Timeline

2026-06-04: Report received 2026-06-04: Report acknowledged 2026-06-08: Report verified 2026-06-17: Fix ready for 1.11.x 2026-06-22: Fix ported to 2.0.0 2026-06-23: Fix released with 1.11.8 and 2.0.0rc3