SOC status:Duty analyst on shift

UK Cyber Defence
VulnerabilityAnalyzed

CVE-2026-23964

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.

MEDIUM 5.4EPSS 0.21%

Does this matter?

Lower severity and a low EPSS score (0.21%). Track it; it rarely justifies an emergency change on its own.

Description

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.

CVSS 3.1
5.4 MEDIUMCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
EPSS
0.21% probability · 11th percentile
CISA KEV
Not listed
Weakness
CWE-863, CWE-639
Affected
joinmastodon/mastodon
Source
security-advisories@github.com

References

Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.