What is the CVSS score of CVE-2021-3901?

CVE-2021-3901 has a CVSS 3.1 base score of 8.8 (High). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H. EPSS exploitation probability: 0.5%.

Is there a public PoC exploit available for CVE-2021-3901?

Yes, a public proof-of-concept exploit is available for CVE-2021-3901. Prioritise patching immediately. EPSS: 0.5%.

Is there a patch available for CVE-2021-3901?

Yes, a patch is available for CVE-2021-3901. Update the affected software to the latest version immediately.

Firefly Iii CVE-2021-3901

HIGH

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

2021-10-27 security@huntr.dev

CSRF Firefly Iii

8.8

CVSS 3.1 · NVD

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Vulnerability Assessment

Weakness	CWE CWE-352 OWASP Top 10:2025 A01:2025 - Broken Access Control ASVS 5.0 V3 - Web Frontend Security Anti-CSRF tokens, SameSite cookies MITRE ATT&CK 1 technique across 1 tactic: Initial Access The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. Sign in to read
Impact	CVSS score of 8.8 (HIGH). Attack characteristics: network attack vector, low complexity, no privileges required, user interaction required. Public proof-of-concept exploit code is available.
Exploit ScenarioDerived	A remote attacker could trick authenticated users into performing unintended actions by sending crafted requests to the affected application. No authentication is required to exploit this vulnerability.

This Week Schedule remediation this week. Why: HIGH severity (CVSS 7.0-8.9).

Patch available 0.5% exploitation probability (EPSS)

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AnalysisAI

firefly-iii is vulnerable to Cross-Site Request Forgery (CSRF). Rated high severity (CVSS 8.8), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available.

RemediationAI

A vendor patch is available. Apply the latest security update as soon as possible. Implement anti-CSRF tokens, validate Origin/Referer headers, use SameSite cookie attribute.

Affected Packages

composer grumpydictator/firefly-iii no fix

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 1 package in composer

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

Technical ContextAI · show details

This vulnerability is classified as Cross-Site Request Forgery (CSRF) (CWE-352), which allows attackers to trick authenticated users into performing unintended actions. firefly-iii is vulnerable to Cross-Site Request Forgery (CSRF) Affected products include: Firefly-Iii Firefly Iii.

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Check this CVE against your own stack and servers
Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

NVD PRIMARY 8.8 HIGH

AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

Required

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

DescriptionNVD

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

Threat Intelligence Overview

EPSS Score

0.5%

Top 59% exploitable

Exploit

POC

Public exploit code exists

Data Quality

3 sources

Confidence: Low

NVD

CVE.org

EPSS

GitHub

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue

Severity HIGH

CISA KEV No

Public POC Yes

EPSS 0.5%

Patch available Yes

Active threat No

Deciding rule

HIGH severity (CVSS 7.0-8.9)

What every action level means

Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.

Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.

This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.

This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.

Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived

Scheduled

Exploitation· derived

Poc

System Exposure· derived

Open

Automatable· derived

Human Impact· derived

Medium

Priority Score

Low Medium High Critical

KEV: 0

EPSS: +1

CVSS: +44

PoC: +20

Weaponized: 0

Threat intel: 0

Gov advisory: 0

Attack Technique

Cross-Site Request Forgery MEDIUM

Cross-Site Request Forgery exploits the automatic credential inclusion behavior of web browsers.

Affected Products (CPE)NVD

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

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References

Advisories & patches

PATCH https://github.com/firefly-iii/firefly-iii/commit/b42d8d1e305cad70d9b83b33cd8e0d7a4b2060c2

Search Externally

GitHub PoC

Exploit-DB PacketStorm Snyk Rapid7 Nuclei Templates Trickest PoC

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