CVE-2026-23964Network attack vector

Push disruption via unchecked subscription ownership

Published Jan 22, 2026 · Updated Jan 22, 2026

Incorrect authorization in affected Mastodon releases allows remote authenticated users to alter other users' web push subscriptions. The web push subscription update endpoint accepts a caller-controlled numeric subscription ID without verifying ownership and returns the subscription object, including its endpoint. A valid account and a guessed or obtained ID are sufficient to change notification filters and subscribed event types, disrupting delivery and disclosing the endpoint but not its keypair.

CVSS severity6.5
Medium
EPSS probability0.21%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Incorrect authorization in affected Mastodon releases allows remote authenticated users to alter other users' web push subscriptions. The web push subscription update endpoint accepts a caller-controlled numeric subscription ID without verifying ownership and returns the subscription object, including its endpoint. A valid account and a guessed or obtained ID are sufficient to change notification filters and subscribed event types, disrupting delivery and disclosing the endpoint but not its keypair.

The record

CVE
CVE-2026-23964
Published
Jan 22, 2026
Updated
Jan 22, 2026
Vendor
Mastodon
Product
Mastodon
Classifications
CWE-639, CWE-863
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

Compare your product and version with the public record. A matching version still requires validation against your environment.

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

5.4NISTCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
6.5GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-639Authorization Bypass Through User-Controlled Key
CWE-863Incorrect Authorization

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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