Insecure Direct Object Reference in Mastodon by Mastodon
CVE-2026-23964

6.5MEDIUM

Key Information:

Vendor

Mastodon

Status
Mastodon
Vendor
CVE Published:
22 January 2026

What is CVE-2026-23964?

Mastodon, a free and open-source social network server based on ActivityPub, is vulnerable to an insecure direct object reference in its web push subscription update endpoint. Prior to the corrected versions (4.5.5, 4.4.12, and 4.3.18), this vulnerability enables any authenticated user to manipulate another user's push subscription by guessing or accessing the numeric subscription ID. This exploitation can disrupt notifications for victims by altering their push subscription settings, including filtering preferences and notification types. Furthermore, the endpoint leakage allows unauthorized access to the web push subscription endpoint without exposing sensitive keypair information, thereby increasing the security risks for affected users.

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Affected Version(s)

mastodon < 4.3.18 < 4.3.18

mastodon >= 4.4.0, < 4.4.12 < 4.4.0, 4.4.12

mastodon >= 4.5.0, < 4.5.5 < 4.5.0, 4.5.5

References

https://github.com/mastodon/mastodon/security/advisories/...
x_refsource_CONFIRM
https://github.com/mastodon/mastodon/releases/tag/v4.3.18
x_refsource_MISC
https://github.com/mastodon/mastodon/releases/tag/v4.4.12
x_refsource_MISC

CVSS V3.1

Score:
6.5
Severity:
MEDIUM
Confidentiality:
Low
Integrity:
Low
Availability:
Low
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
None
User Interaction:
None
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

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