# CVE-2021-21479: SCIMono - RCE

> Live exploitation tracking for CVE-2021-21479 by the CrowdSec Live Exploit Tracker, built from real-world attack data crowdsourced from CrowdSec's global network.

Page: https://tracker.crowdsec.net/cves/CVE-2021-21479

## Key facts

- **Exploitation phase:** Limited Exploitation. The vulnerability is known but shows very limited attacker interest or exploitation activity.
- **CVSS score:** 9.1
- **Public exploit available:** Yes
- **Affected products:** SAP SCIMono
- **Weaknesses:** CWE-74 (Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection'))
- **Tags:** enterprise_software

## Description

In SCIMono before 0.0.19, it is possible for an attacker to inject and execute java expression compromising the availability and integrity of the system.

## CrowdSec analysis

[CVE-2021-21479](https://euvd.enisa.europa.eu/vulnerability/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.

Data from the CrowdSec community indicates that exploitation of CVE-2021-21479 is highly selective and intelligence-driven. Threat actors use advanced reconnaissance and carefully choose their targets, often as part of sophisticated campaigns or advanced persistent threat operations.
CrowdSec network telemetry also shows that exploitation of CVE-2021-21479 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.

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

## Timeline

- 2021-02-09: CVE Published. CVE-2021-21479 is published to NVD.
- 2025-05-22: Rule Released. CrowdSec releases a rule to detect CVE-2021-21479 exploitation attempts against the CrowdSec Network.
- 2025-05-23: CrowdSec First Seen. CrowdSec observes in-the-wild exploitation of CVE-2021-21479 for the first time.

## References

- https://github.com/SAP/scimono/security/advisories/GHSA-29q4-gxjq-rx5c
- https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2021/CVE-2021-21479.yaml

## Live exploitation data

The [Live Exploit Tracker page](https://tracker.crowdsec.net/cves/CVE-2021-21479) follows observed exploitation activity for CVE-2021-21479. [Request an API key](https://tracker.crowdsec.net/request-api-key) for full access to its exploitation timeline, attacking IP addresses and blocklists.