CVE-2021-3921Network attack vector

Forced logout via CSRF-enabled GET route

Published Nov 13, 2021 · Updated Aug 3, 2024

Cross-site request forgery in Firefly III before 5.6.3 allows remote attackers to log authenticated users out via a crafted request. The logout route accepts GET requests, so a crafted cross-origin navigation invokes LoginController@logout without a CSRF token. Exploitation requires an authenticated user to follow or load the crafted URL and terminates only that user's active session.

CVSS severity4.3
Medium
EPSS probability0.44%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cross-site request forgery in Firefly III before 5.6.3 allows remote attackers to log authenticated users out via a crafted request. The logout route accepts GET requests, so a crafted cross-origin navigation invokes LoginController@logout without a CSRF token. Exploitation requires an authenticated user to follow or load the crafted URL and terminates only that user's active session.

The record

CVE
CVE-2021-3921
Published
Nov 13, 2021
Updated
Aug 3, 2024
Vendor
Firefly III
Product
Firefly III
Classifications
CWE-352, T1204.001
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Nov 13, 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 <5.6.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Firefly III · Firefly IIIversion=unspecified <5.6.3

Published CVSS scores

5.4huntr.devCVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:L
4.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:P/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.

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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)
T1204.001Malicious Link

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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