SB2026052304 - Multiple vulnerabilities in Mastodon

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Main Vulnerability Database SB2026052304

SB2026052304 - Multiple vulnerabilities in Mastodon

Published: May 23, 2026

Security Bulletin ID SB2026052304
CSH Severity
High
Patch available
YES
Number of vulnerabilities 5
Exploitation vector Remote access
Highest impact Information disclosure

Breakdown by Severity

High 20% Medium 80%
  • Low
  • Medium
  • High
  • Critical

Description

This security bulletin contains information about 5 vulnerabilities.


1) Improper access control (CVE-ID: CVE-2026-47777)

CWE-ID: CWE-284 - Improper Access Control

CVSSv4: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:U/U:Green


The vulnerability allows a remote attacker to bypass consent checks and falsify authorization for inclusion in a remote collection.

The vulnerability exists due to improper access control in the remote Collections consent verification logic when processing a forged FeatureAuthorization object. A remote attacker can forge a FeatureAuthorization object to bypass consent checks and falsify authorization for inclusion in a remote collection.

Only instances with the experimental "Collections" feature enabled are vulnerable.


2) Server-Side Request Forgery (SSRF) (CVE-ID: CVE-2026-47389)

CWE-ID: CWE-918 - Server-Side Request Forgery (SSRF)

CVSSv4: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:L/SI:N/SA:N/E:U/U:Amber


The vulnerability allows a remote attacker to disclose sensitive information via server-side request forgery.

The vulnerability exists due to incomplete list of disallowed inputs in PrivateAddressCheck.private_address? when processing hostnames that resolve to IPv4-mapped IPv6 addresses. A remote attacker can publish a crafted AAAA record for a domain they control to disclose sensitive information via server-side request forgery.

On affected Ruby versions, outbound HTTP fetches can reach loopback, private network, link-local, and cloud metadata addresses through such mapped addresses.


3) Server-Side Request Forgery (SSRF) (CVE-ID: CVE-2026-46348)

CWE-ID: CWE-918 - Server-Side Request Forgery (SSRF)

CVSSv4: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:U/U:Green


The vulnerability allows a remote attacker to access otherwise private resources and services via server-side request forgery.

The vulnerability exists due to improper restriction of requests in outbound request handling when processing user-provided domains. A remote attacker can supply an IPv6 unspecified address (::) to make Mastodon perform HTTP requests against loopback interfaces to access otherwise private resources and services via server-side request forgery.


4) Improper Verification of Cryptographic Signature (CVE-ID: CVE-2026-46349)

CWE-ID: CWE-347 - Improper Verification of Cryptographic Signature

CVSSv4: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:U/U:Green


The vulnerability allows a remote attacker to spoof activity integrity.

The vulnerability exists due to improper verification of cryptographic signature in Linked-Data Signature normalization of incoming activities when processing signed JSON-LD activities. A remote attacker can re-arrange a valid signed JSON-LD activity from a third-party actor to have it processed differently to spoof activity integrity.

The demonstrated impact is limited to re-issuing retracted boost (Announce) activities from a third-party user without their involvement.


5) Input validation error (CVE-ID: CVE-2026-48028)

CWE-ID: CWE-20 - Improper input validation

CVSSv4: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N/E:U/U:Green


The vulnerability allows a remote attacker to selectively hide contents of a signed activity.

The vulnerability exists due to improper input validation in incoming activity normalization for Linked-Data Signatures when processing signed activities from a third-party actor. A remote attacker can remove JSON entries from a valid signed activity to selectively hide contents of a signed activity.

Exploitation requires access to the original signed activity object.


Remediation

Install update from vendor's website.

References