CVE-2026-23964

What it is

Mastodon is a free, open-source social network server based on ActivityPub. Prior to versions 4.5.5, 4.4.12, and 4.3.18, an insecure direct object reference in the web push subscription update endpoint lets any authenticated user update another user's push subscription by guessing or obtaining the numeric subscription id. This can be used to disrupt push notifications for other users and also leaks the web push subscription endpoint. Any user with a web push subscription is impacted, because another authenticated user can tamper with their push subscription settings if they can guess or obtain the subscription id. This allows an attacker to disrupt push notifications by changing the policy (whether to filter notifications from non-followers or non-followed users) and subscribed notification types of their victims. Additionally, the endpoint returns the subscription object, which includes the push notification endpoint for this subscription, but not its keypair. Mastodon versions v4.5.5, v4.4.12, v4.3.18 are patched.

At a glance

Exploitability

Can be exploited over the network without logging in. Limited direct impact.

Exploit odds

0.2% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2026-01-22 03:15 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-06-17 10:22 UTC Last updatedMost recent change to the record

Details

Published

2026-01-22 03:15 UTC

Last modified

2026-06-17 10:22 UTC

Exploit probability

0.2% · EPSS, next 30 days

Weakness

CWE-863 · Incorrect authorization

Record status

Analyzed

Affected

• Joinmastodon Mastodon < 4.3.18
• Joinmastodon Mastodon < 4.4.12
• Joinmastodon Mastodon < 4.5.5

Attack profile CVSS 3.1 · 6.5

Attack vector

Network

Complexity

Low

Privileges needed

None

User interaction

None

Scope

Unchanged

Confidentiality

Low

Integrity

Low

Availability

None