What is the CVSS score of CVE-2026-46349?

CVE-2026-46349 has a CVSS 3.1 base score of 5.3 (Medium). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N. EPSS exploitation probability: 0.2%.

Is there a patch available for CVE-2026-46349?

Yes, a patch is available for CVE-2026-46349. Update the affected software to the latest version immediately.

Mastodon CVE-2026-46349

EUVD-2026-39054 MEDIUM

Improper Verification of Cryptographic Signature (CWE-347)

2026-06-24 GitHub_M

Information Disclosure Jwt Attack Mastodon

5.3

CVSS 3.1 · Vendor: GitHub_M

Severity by source

Vendor (GitHub_M) PRIMARY

5.3 MEDIUM

AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

vuln.today AI

5.3 MEDIUM

Network-delivered attack requiring no privileges or interaction; integrity-only impact confined to the vulnerable system's activity processing with no scope change.

3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

4.0 AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N

Primary rating from Vendor (GitHub_M).

CVSS VectorVendor: GitHub_M

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

Low

Availability

None

Lifecycle Timeline

Patch available

Jun 24, 2026 - 21:02 EUVD

Analysis Generated

Jun 24, 2026 - 20:23 vuln.today

DescriptionCVE.org

Mastodon is a free, open-source social network server based on ActivityPub. Prior to 4.5.10, 4.4.17, and 4.3.23, Mastodon's normalization of incoming activities signed with Linked-Data Signatures does not sufficiently protect the activities from a certain class of spoofing, allowing attackers to re-arrange a valid signed JSON-LD activity from a third-party actor to have it processed differently. This vulnerability is fixed in 4.5.10, 4.4.17, and 4.3.23.

AnalysisAI

Linked-Data Signature normalization in Mastodon's ActivityPub federation layer permits activity spoofing against servers running versions prior to 4.5.10, 4.4.17, and 4.3.23. An attacker can take a legitimately signed JSON-LD activity from a real third-party actor, re-arrange its structure, and relay it to a target Mastodon instance where it passes signature validation but is interpreted with altered semantic meaning. No public exploit has been identified at time of analysis, and this vulnerability is not listed in CISA KEV, though the integrity impact on federated social graph trust is meaningful for operators of public-facing instances.

Technical ContextAI

Mastodon implements the ActivityPub W3C protocol for federated social networking, using JSON-LD (Linked Data in JSON) for activity representation and Linked-Data Signatures (LD-Signatures) for verifying the authenticity of cross-server activity delivery. JSON-LD documents must be canonicalized before signature verification - a process that normalizes equivalent representations into a canonical form. CWE-347 (Improper Verification of Cryptographic Signature) is the root cause class: the canonicalization/normalization step does not sufficiently constrain which structural re-arrangements of the JSON-LD object are considered equivalent, allowing an attacker to rearrange property ordering or framing in a signed document such that it both passes signature verification and is parsed with different semantic intent. This is analogous to canonicalization confusion attacks seen in XML-DSIG and SAML contexts. Affected CPE: cpe:2.3:a:mastodon:mastodon:*:*:*:*:*:*:*:* covering all versions before the patched releases.

RemediationAI

Upgrade to Mastodon 4.5.10, 4.4.17, or 4.3.23, which contain the fix for the Linked-Data Signature normalization flaw, as confirmed by the vendor advisory GHSA-chgx-jx3p-rf73 at https://github.com/mastodon/mastodon/security/advisories/GHSA-chgx-jx3p-rf73. Instances running unsupported branches (4.2.x and earlier) should migrate to a supported branch at the earliest opportunity, as no patch is available for those versions. As a partial compensating control, administrators may consider temporarily restricting federation to a tightly controlled allowlist of trusted remote servers, which reduces the attack surface by limiting the pool of third-party signed activities the instance will process - but this trade-off significantly degrades fediverse connectivity and is only appropriate as a short-term measure. There is no known configuration toggle to disable Linked-Data Signature processing independently of ActivityPub federation.