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hackeroneRullzerH1:1965156
HistoryApr 28, 2023 - 9:52 a.m.

Nextcloud: Text does not respect 'Allow download' permissions

2023-04-2809:52:05
rullzer
hackerone.com
$250
4
nextcloud
allow download
permissions
bypass
vulnerability
bugbounty

4.3 Medium

CVSS3

Attack Vector

NETWORK

Attack Complexity

LOW

Privileges Required

NONE

User Interaction

REQUIRED

Scope

UNCHANGED

Confidentiality Impact

LOW

Integrity Impact

NONE

Availability Impact

NONE

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N

4.3 Medium

CVSS2

Access Vector

NETWORK

Access Complexity

MEDIUM

Authentication

NONE

Confidentiality Impact

PARTIAL

Integrity Impact

NONE

Availability Impact

NONE

AV:N/AC:M/Au:N/C:P/I:N/A:N

0.001 Low

EPSS

Percentile

20.6%

  1. user0 shares a folder of sensitive images to user1 without the β€˜Allow download’ permission
  2. user1 just creates a new text file and inserts the images into it
  3. Voilla the images appear and can be downloaded easily

These are just previews but still.
For the most common types you can even request the raw image https://github.com/nextcloud/text/blob/main/lib/Controller/AttachmentController.php#L57-L67

Impact

A user assume that the allow download feature works can still have their sensitive photos leaked.

4.3 Medium

CVSS3

Attack Vector

NETWORK

Attack Complexity

LOW

Privileges Required

NONE

User Interaction

REQUIRED

Scope

UNCHANGED

Confidentiality Impact

LOW

Integrity Impact

NONE

Availability Impact

NONE

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N

4.3 Medium

CVSS2

Access Vector

NETWORK

Access Complexity

MEDIUM

Authentication

NONE

Confidentiality Impact

PARTIAL

Integrity Impact

NONE

Availability Impact

NONE

AV:N/AC:M/Au:N/C:P/I:N/A:N

0.001 Low

EPSS

Percentile

20.6%