SCIMono - RCE (CVE-2021-21479)

CVE-2021-21479 is a serious vulnerability in SCIMono that enables attackers to inject and execute Java expressions, leading to potential compromise of system availability and integrity.

CrowdSec has been tracking this vulnerability and its exploits since 22nd of May 2025.

CrowdSec network observations suggest that most exploitation of CVE-2021-21479 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. In addition, according to the CrowdSec network, attack volume against CVE-2021-21479 has dipped slightly compared to the previous week. Although still commonly targeted, the decline suggests a cooling-off period. Long-term relevance remains, but attention is waning.

Exploitation attempts commonly target URLs that start with /schemas/ and include suspicious Java expression patterns.