CVE-2021-3900Network attack vector

Rule duplication and reordering via CSRF-prone GET routes

Published Oct 27, 2021 · Updated Aug 3, 2024

CSRF in Firefly III 5.6.2 and earlier allows remote attackers to duplicate rules or reorder rule groups through a logged-in user's browser. The rules interface exposed duplicate, move-up, and move-down actions as state-changing GET routes, so cross-origin requests could invoke them without a CSRF token. A victim must be authenticated and load attacker-controlled content; the demonstrated consequence is limited to duplicating rules and changing rule-group order.

CVSS severity6.5
Medium
EPSS probability0.55%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

CSRF in Firefly III 5.6.2 and earlier allows remote attackers to duplicate rules or reorder rule groups through a logged-in user's browser. The rules interface exposed duplicate, move-up, and move-down actions as state-changing GET routes, so cross-origin requests could invoke them without a CSRF token. A victim must be authenticated and load attacker-controlled content; the demonstrated consequence is limited to duplicating rules and changing rule-group order.

The record

CVE
CVE-2021-3900
Published
Oct 27, 2021
Updated
Aug 3, 2024
Vendor
Firefly III
Product
Firefly III
Classifications
CWE-352, T1185
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 27, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=unspecified <=5.6.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Firefly III · Firefly IIIversion=unspecified <=5.6.2

Published CVSS scores

4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:P/A:N
4.3huntr.devCVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
6.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-352Cross-Site Request Forgery (CSRF)
T1185Browser Session Hijacking

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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