CVE-2021-3846Network attack vector

Authenticated resource exhaustion via undeleted rejected uploads

Published Oct 19, 2021 · Updated Aug 3, 2024

Unrestricted upload in Firefly III before 5.6.2 allows remote authenticated users to retain rejected API uploads as temporary files. AttachmentHelper::saveAttachmentFromApi returns after rejecting a disallowed MIME type without closing the temporary resource, so the file is not deleted. Repeated rejected uploads consume temporary storage and can interrupt service; the published patch does not show persistence or execution of uploaded code.

CVSS severity8.8
High
EPSS probability0.78%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Unrestricted upload in Firefly III before 5.6.2 allows remote authenticated users to retain rejected API uploads as temporary files. AttachmentHelper::saveAttachmentFromApi returns after rejecting a disallowed MIME type without closing the temporary resource, so the file is not deleted. Repeated rejected uploads consume temporary storage and can interrupt service; the published patch does not show persistence or execution of uploaded code.

The record

CVE
CVE-2021-3846
Published
Oct 19, 2021
Updated
Aug 3, 2024
Vendor
Firefly III
Product
Firefly III
Classifications
CWE-434, T1499
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Oct 19, 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 privilegesauthenticated

What is affected?

Firefly III · Firefly IIIversion=unspecified <5.6.2

Published CVSS scores

6.3Huntr CNACVSS:3.0/AV:L/AC:H/PR:H/UI:R/S:U/C:H/I:H/A:H
8.8GitHub Advisory DatabaseCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

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
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-434Unrestricted Upload of File with Dangerous Type
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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