How severe is CVE-2021-3851?

CVE-2021-3851 has a CVSS 3.x base score of 5.4, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.

Is CVE-2021-3851 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (42nd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-3851?

CVE-2021-3851 affects Firefly-iii Firefly Iii. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-3851?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2021-3851 published?

CVE-2021-3851 was published on 2021-10-19 and last updated on 2026-06-17.

CVE-2021-3851

CVE-2021-3851 is a medium-severity vulnerability in Firefly-iii Firefly Iii with a CVSS 3.x base score of 5.4. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-601.

Key facts

Severity: Medium (CVSS 3.x base score 5.4)
CVSS v2: 4.9
EPSS exploit prediction: 1% (42nd percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-601
Affected product: Firefly-iii Firefly Iii
Published: 2021-10-19
Last modified: 2026-06-17

Description

firefly-iii is vulnerable to URL Redirection to Untrusted Site

Frequently asked questions

What is CVE-2021-3851?: firefly-iii is vulnerable to URL Redirection to Untrusted Site
How severe is CVE-2021-3851?: CVE-2021-3851 has a CVSS 3.x base score of 5.4, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.
Is CVE-2021-3851 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (42nd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-3851?: CVE-2021-3851 affects Firefly-iii Firefly Iii. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-3851?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-3851 published?: CVE-2021-3851 was published on 2021-10-19 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:firefly-iii:firefly_iii:*:*:*:*:*:*:*:*

More vulnerabilities in Firefly-iii Firefly Iii

CVE-2023-1788 — Critical (CVSS 9.8): Insufficient Session Expiration in GitHub repository firefly-iii/firefly-iii prior to 6.
CVE-2023-1789 — Critical (CVSS 9.8): Improper Input Validation in GitHub repository firefly-iii/firefly-iii prior to 6.0.0.
CVE-2021-3901 — High (CVSS 8.8): firefly-iii is vulnerable to Cross-Site Request Forgery (CSRF)
CVE-2021-3846 — High (CVSS 8.8): firefly-iii is vulnerable to Unrestricted Upload of File with Dangerous Type
CVE-2021-3819 — High (CVSS 8.8): firefly-iii is vulnerable to Cross-Site Request Forgery (CSRF)
CVE-2021-3663 — High (CVSS 7.5): firefly-iii is vulnerable to Improper Restriction of Excessive Authentication Attempts

All CVEs affecting Firefly-iii Firefly Iii →

Other CWE-601 (Open Redirect) vulnerabilities

CVE-2018-3774 — Critical (CVSS 10.0): Incorrect parsing in url-parse <1.4.3 returns wrong hostname which leads to multiple vulnerabilities such as SSRF, Open…
CVE-2019-25282 — Critical (CVSS 9.8): V-SOL GPON/EPON OLT Platform v2.03 contains an open redirect vulnerability in the script that allows attackers to…
CVE-2020-36912 — Critical (CVSS 9.8): Plexus anblick Digital Signage Management 3.1.13 contains an open redirect vulnerability in the 'PantallaLogin' script…
CVE-2025-43526 — Critical (CVSS 9.8): This issue was addressed with improved URL validation. This issue is fixed in Safari 26.2, macOS Tahoe 26.2. On a Mac…
CVE-2025-55031 — Critical (CVSS 9.8): Malicious pages could use Firefox for iOS to pass FIDO: links to the OS and trigger the hybrid passkey transport. An…
CVE-2024-22891 — Critical (CVSS 9.8): Nteract v.0.28.0 was discovered to contain a remote code execution (RCE) vulnerability via the Markdown link.

Browse all CWE-601 (Open Redirect) vulnerabilities →