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Misskey's missing signature validation allows arbitrary users to impersonate any remote user.

Critical
syuilo published GHSA-3f39-6537-3cgc Nov 25, 2023

Package

No package listed

Affected versions

<=2023.11.0

Patched versions

2023.11.1-beta.1

Description

Authors

@yunochi*, @perillamint*

Summary

Misskey's missing signature validation allows arbitrary users to impersonate any remote user.

Details

When Misskey has to verify the remote actor is eligible to POST into
the inbox, it only validates its HTTP message signature.

Due to lack of the header validation such as Digest and Host, it allows
attackers can spoof arbitrary users using ActivityPub server-to-server federation
protocol.

Severity

CVSS v4.0 score: 7.1 (High)

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

CVSS v3.1 score: 9.3 (Critical)

Vector String: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:H/A:N

PoC

Included in mailed tarball. See /exploit

Possible mitigation

Server administrators

Configure the reverse proxy to explicitly filter out the requests with a
non-matching HOST header. Since most ActivityPub implementation which
uses HTTP message signature to authenticate server-to-server federation
includes HOST in their signature, it will provide a not-perfect-but-practical
defense against this attack.

Also, use a firewall to block external requests bypassing the reverse
proxy.

This vulnerability has been fixed in v2023.11.1; updating to v2023.11.1 or later is strongly recommended.

Misskey maintainers

There is a patch that implements missing validation and submitted using the GHSA private fork feature. See branch advisory-fix-1 for the patch.

Severity

Critical

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Changed
Confidentiality
Low
Integrity
High
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:H/A:N

CVE ID

CVE-2023-49079

Weaknesses

Credits