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🛡️ CVE-2022-39335 — matrix-synapse

🟠 CVSS 8.0 — High ✅ No Known Exploit CWE-200 NVD
8.0
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

Synapse does not apply enough checks to servers requesting auth events of events in a room

Impact

Synapse is an open-source Matrix homeserver written and maintained by the Matrix.org Foundation. The Matrix Federation API allows remote homeservers to request the *authorisation events* of events in a room. This is necessary so that a homeserver receiving some events can validate that those events are legitimate and permitted in their room.

However, in versions of Synapse up to and including 1.68.0, a Synapse homeserver answering a query for authorisation events does not sufficiently check that the requesting server should be able to access them.

Authorisation events include power level events (the list of user IDs and their power levels at the time) and relevant membership events (including the display name of the sender of that event), as well as events like m.room.create, m.room.third_party_invite and m.room.join_rules. Non-authorisation events are unaffected, so it isn't possible to e.g. extract message contents this way.

This issue is only exploitable when a malicious actor knows the ID of a target room and the ID of an event from that room. In most cases, this makes exploitation infeasible. This issue is of negligible consequence for public rooms given that any server can easily join the room in order to be allowed to view authorisation events. Further, deployments in a closed federation where all homeservers are trustworthy are not affected.

Patches

The issue was patched in Synapse 1.69.0. Homeserver administrators are advised to upgrade.

Workarounds

Synapse can be configured with a list of servers that it is allowed to federate with [federation_domain_whitelist]. If this list is in use and all the servers on the list are trusted not to exploit this issue, then this issue is of no consequence.

This workaround is not practical for homeservers participating in open federation as interaction with any server not on the list would have to happen indirectly through servers that are, leading to inconsistent delays in message delivery.

[federation_domain_whitelist]: https://matrix-org.github.io/synapse/v1.68/usage/configuration/config_documentation.html#federation_domain_whitelist

References

Fixed in https://github.com/matrix-org/synapse/pull/13823.

For more information

If you have any questions or comments about this advisory, e-mail us at security@matrix.org.

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is high, an attacker needs low-level privileges on the target. No user interaction is required. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality low, integrity low, availability low.

CVSS metrics in full

The score comes from this vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:L

  • Attack vector: Network — reachable from anywhere that can route to the service.
  • Attack complexity: High — the attacker first has to win a race, learn a secret or otherwise prepare the target.
  • Privileges required: Low — an ordinary user account is enough.
  • User interaction: None — nobody has to be tricked into anything.
  • Scope: Unchanged — the damage stays inside the vulnerable component.
  • Confidentiality impact: Low — limited, and the attacker does not choose what is affected.
  • Integrity impact: Low — limited, and the attacker does not choose what is affected.
  • Availability impact: Low — limited, and the attacker does not choose what is affected.

Weakness class

CVE-2022-39335 is classified as CWE-200: Exposure of Sensitive Information. Information that should stay internal is disclosed to someone who is not authorised to see it.

Affected software

CVE-2022-39335 is recorded against 2 packages.

  • matrix-synapse (fixed in 1.69.0)
  • synapse (fixed in 1.69.0)

Timeline and source

Published on 24 May 2023 and last revised on 24 September 2024. No public exploit is currently recorded for this entry. A vendor advisory or fix has been published. Record sourced from NVD.

References

github.com (Web)
nvd.nist.gov (Advisory)
github.com (Web)
github.com (Web)
github.com (Package)
github.com (Web)
lists.fedoraproject.org (Web)

Other advisories for this package

matrix-synapse has other advisories on record. If you are patching this one, these are worth checking on the same host:

Same weakness in other software

These advisories are the same class of weakness (CWE-200: Exposure of Sensitive Information) in other software:

CVE-2022-39335 on other distributions

Each distribution ships its own build and its own fixed version. Pick the one you run:

Details

Severity HIGH
CVSS Score 8.0
CVSS Vector CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:L
CWE CWE-200
Public Exploit ✅ No
Source NVD
Published 2023-05-24
Updated 2026-08-20
Modified 2024-09-24

Affected Packages

Software From version Fixed in
matrix-synapse — 1.69.0
synapse — 1.69.0

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