BEMS API - Arbitrary File Read (CVE-2021-4463)

CVE-2021-4463 is a high-severity vulnerability in Longjing Technology BEMS API up to version 1.21, where the 'downloads' endpoint fails to properly sanitize the 'fileName' parameter. This flaw allows unauthenticated attackers to exploit directory traversal and download arbitrary files from the server, potentially exposing sensitive system or configuration data. Attackers could leverage this vulnerability to gain unauthorized access to confidential information, increasing the risk of further compromise.

CrowdSec has been tracking this vulnerability and its exploits since 3rd of June 2026.

CrowdSec network observations suggest that most exploitation of CVE-2021-4463 involves focused reconnaissance to identify viable targets. Attackers typically tailor their campaigns based on system exposure and configuration. It is unlikely that a given attack is accidental. CrowdSec network telemetry also shows that exploitation of CVE-2021-4463 has significantly declined over the past week. Attack volumes are well below the long-term average, suggesting attackers are rapidly losing interest. The vulnerability appears to be falling out of active use across most threat landscapes.

Attackers exploit the /api/downloads endpoint by supplying directory traversal sequences in the fileName parameter to download arbitrary files from the server.