CVE-2020-26257: Denial of service attack via incorrect parameters to federation APIs
Impact
A malicious or poorly-implemented homeserver can inject malformed events into a room by specifying a different room id in the path of a /sendjoin, /sendleave, /invite or /exchangethirdpartyinvite request.
This can lead to a denial of service in which future events will not be correctly sent to other servers over federation.
This affects any server which accepts federation requests from untrusted servers.
Patches
Issue is resolved by https://github.com/matrix-org/synapse/pull/8776.
Workarounds
Homeserver administrators could limit access to the federation API to trusted servers (for example via federationdomainwhitelist).
Other sources
Matrix is an ecosystem for open federated Instant Messaging and VoIP. Synapse is a reference "homeserver" implementation of Matrix. A malicious or poorly-implemented homeserver can inject malformed events into a room by specifying a different room id in the path of a /sendjoin, /sendleave, /invite or /exchangethirdpartyinvite request. This can lead to a denial of service in which future events will not be correctly sent to other servers over federation. This affects any server which accepts federation requests from untrusted servers. The Matrix Synapse reference implementation before version 1.23.1 the implementation is vulnerable to this injection attack. Issue is fixed in version 1.23.1. As a workaround homeserver administrators could limit access to the federation API to trusted servers (for example via federationdomainwhitelist).
Affected Software
Remediation
Patch Available
Event History
Frequently Asked Questions
What is the severity of CVE-2020-26257?
CVE-2020-26257 has a severity rating that can lead to Denial of Service attacks.
How do I fix CVE-2020-26257?
To fix CVE-2020-26257, update your Matrix Synapse to version 1.23.1 or later.
What software is affected by CVE-2020-26257?
CVE-2020-26257 affects Matrix Synapse versions prior to 1.23.1, as well as Fedora 32 and 33.
What causes CVE-2020-26257?
CVE-2020-26257 is caused by a malicious or poorly-implemented homeserver injecting malformed events by specifying a different room ID.
Can CVE-2020-26257 lead to data breaches?
CVE-2020-26257 primarily leads to denial of service rather than direct data breaches.