CVE-2026-23963Network attack vector

Authenticated resource exhaustion via unbounded user fields

Published Jan 22, 2026 · Updated Jan 22, 2026

Resource exhaustion in Mastodon before 4.3.18, 4.4.0 through 4.4.11, and 4.5.0 through 4.5.4 allows remote authenticated users to consume resources. List and filter APIs accept arbitrarily long list names, filter names, and filter keywords because the server applies no maximum-length validation before storing and processing them. Any local account can trigger disproportionate storage and computing use; a malicious API client can also make that account's web interface unusable.

CVSS severity4.3
Medium
EPSS probability0.32%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Resource exhaustion in Mastodon before 4.3.18, 4.4.0 through 4.4.11, and 4.5.0 through 4.5.4 allows remote authenticated users to consume resources. List and filter APIs accept arbitrarily long list names, filter names, and filter keywords because the server applies no maximum-length validation before storing and processing them. Any local account can trigger disproportionate storage and computing use; a malicious API client can also make that account's web interface unusable.

The record

CVE
CVE-2026-23963
Published
Jan 22, 2026
Updated
Jan 22, 2026
Vendor
Mastodon
Product
Mastodon
Classifications
CWE-770, T1496
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Jan 22, 2026CVE publishedPublication date reported by the CVE source.
  2. Jan 22, 2026Record 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=< 4.3.18
  2. Affected versionversion=>= 4.4.0, < 4.4.12
  3. Affected versionversion=>= 4.5.0, < 4.5.5

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Mastodon · Mastodonversion=< 4.3.18; version=>= 4.4.0, < 4.4.12; version=>= 4.5.0, < 4.5.5

Published CVSS scores

4.3GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
6.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/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-770Allocation of Resources Without Limits or Throttling
T1496Resource Hijacking

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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