{"cve":"CVE-2021-41380","nvd":{"published":"2021-09-17T20:15:07.827","modified":"2026-06-17T04:08:26.977","status":"Modified","description":"RealVNC Viewer 6.21.406 allows remote VNC servers to cause a denial of service (application crash) via crafted RFB protocol data. NOTE: It is asserted that this issue requires social engineering a user into connecting to a fake VNC Server. The VNC Viewer application they are using will then hang, until terminated, but no memory leak occurs - the resources are freed once the hung process is terminated and the resource usage is constant during the hang. Only the process that is connected to the fake Server is affected. This is an application bug, not a security issue","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H","score":6.5},"cwes":["CWE-20"],"references":["https://gist.github.com/totaam/a90f2bb40f5b693ccec0ae903d021b03","https://gist.github.com/totaam/a90f2bb40f5b693ccec0ae903d021b03"],"products":["realvnc:vnc_viewer"],"source":"nvd","synced_at":"2026-10-19T21:23:41.316049955+00:00"},"epss":{"cve":"CVE-2021-41380","score":0.00956,"percentile":0.61438,"date":"2026-10-31"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}