What is CVE-2021-3921?

CVE-2021-3921 is a medium-severity vulnerability in Firefly-Iii Firefly Iii, classified under Cross-Site Request Forgery (CSRF). CVSS score: 4.3/10. Published 2021-11-13.

How severe is CVE-2021-3921?

Medium severity. CVSS v3 base score is 4.3 out of 10.

CSRF in Firefly-Iii Firefly Iii

CVE-2021-3921

firefly-iii is vulnerable to Cross-Site Request Forgery (CSRF)

Vulnerability class: CSRF (Cross-Site Request Forgery)

Published 2021-11-13 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 4.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N.

EPSS exploit prediction

EPSS: 0.004 (36.0th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 36th percentile — 36.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · change: +0.000

Affected products

Firefly-Iii Firefly Iii
Firefly-Iii Firefly-Iii/firefly-Iii — versions unspecified

Weakness classification (CWE)

CWE-352 — Cross-Site Request Forgery (CSRF)

References

huntr.dev/bounties/724d3fd5-9f04-45c4-98d6-35a7d15468f5 (Exploit, Patch, Third Party Advisory)
github.com/firefly-iii/firefly-iii/commit/47fa9e39561a9ec9e210e4023d090a7b33381… (Patch, Third Party Advisory)

Frequently asked questions

What is CVE-2021-3921?: CVE-2021-3921 is a medium-severity vulnerability in Firefly-Iii Firefly Iii, classified under Cross-Site Request Forgery (CSRF). CVSS score: 4.3/10. Published 2021-11-13.
How severe is CVE-2021-3921?: Medium severity. CVSS v3 base score is 4.3 out of 10.