Technical Advisory – SonicWall SMA 100 Series – Heap-Based Buffer Overflow (CVE-2021-20043)

Vendor: SonicWall
Vendor URL:
Versions affected:,
Systems Affected: SMA 100 Series (SMA 200, 210, 400, 410, 500v)
Author: Richard Warren <richard.warren[at]nccgroup[dot]trust>
Advisory URL:
CVE Identifier: CVE-2021-20043
Risk: CVSS 8.8 (High)


SonicWall SMA 100 Series appliances running firmware versions, and below suffer from a heap-based buffer overflow vulnerability in the sonicfiles RAC_GET_BOOKMARKS_HTML5 API. This vulnerability arises due to the unchecked use of the strcat function on a fixed size buffer, when displaying user bookmarks. This vulnerability requires authentication as a low privileged user.


An authenticated low-privileged user could exploit this vulnerability to achieve code execution as the nobody user.


The sonicfiles RAC_GET_BOOKMARKS_HTML5 (RacNumber 35) method allows users list their bookmarks. This method is vulnerable to heap-based buffer-overflow, due to unchecked use of strcat.

The RAC_GET_BOOKMARKS sonicfiles method maps to the Python method get_bookmarks. This simply calls into sonicapp.api.getBookmarks:

getBookmarks is a swig wrapper into!getFileShareBookmarks. The following screenshot shows decompilation of the getFileShareBookmarks function:

As shown above, a fixed buffer of size 1280 bytes is allocated. Later, all bookmarks for the current user (specified in the swap ID cookie) are retrieved from the database via a call to bookmarkFindAllByUser.

The following screenshot shows the SQLite query used to retrieve the list of user’s bookmarks in bookmarkFindAllByUser:

The list of bookmarks is then copied (in 128-byte chunks) into the fixed size buffer using strcat:

An attacker could trigger a heap-based buffer overflow by creating 11 bookmarks with a name length of 127 characters, as per the following screenshot:

Once the bookmarks are placed, the attacker could then call the sonicfiles RAC_GET_BOOKMARKS_HTML5 (RacNumber 35) method, to list the bookmarks. This results in a heap-based buffer-overflow in!getFileShareBookmarks->strcat

This vulnerability requires a low-privileged user-level session and could result in code execution as the nobody user.

The following POST request shows the creation of a CIFS server bookmark:

Example POST request to trigger the overflow (after creating the 11 bookmarks):


Upgrade to SMA version, or above.

Vendor Communication

2021-10-29 - Vulnerability reported to SonicWall PSIRT.
2021-11-02 - Acknowledgement from SonicWall PSIRT.
2021-12-01 - SonicWall request that NCC Group withhold technical details until 2022-01-11, releasing high-level advisories on 2021-12-09.
2021-12-03 - NCC Group agrees to suggested disclosure timeline.
2021-12-07 - Patch released and SonicWall publish KB article and security advisory.
2021-12-09 - NCC Group advisory released.

Thanks to

Jennifer Fernick and Aaron Haymore from NCC Group for their assistance with disclosure.

About NCC Group

NCC Group is a global expert in cybersecurity and risk mitigation, working with businesses to protect their brand, value and reputation against the ever-evolving threat landscape. With our knowledge, experience and global footprint, we are best placed to help businesses identify, assess, mitigate & respond to the risks they face. We are passionate about making the Internet safer and revolutionizing the way in which organizations think about cybersecurity.

Published Date: 2021-12-09

Written By: Richard Warren