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MSC4380: Invite blocking #4380

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@richvdh richvdh commented Nov 18, 2025 •
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An alternative to MSC4155.

Written wearing my Spec Core Team hat, in an attempt to unblock the situation that matrix.org and Element-Web have implemented an unspecced MSC which we can't turn off.

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Server implementation: element-hq/synapse#19203
Client implementation: element-hq/element-web#31268

SCT Stuff:

FCP tickyboxes

MSC checklist

@richvdh richvdh changed the title Invite blocking MSC4380: Invite blocking Nov 18, 2025
@turt2live turt2live added proposal A matrix spec change proposal client-server Client-Server API kind:core MSC which is critical to the protocol's success needs-implementation This MSC does not have a qualifying implementation for the SCT to review. The MSC cannot enter FCP. safety labels Nov 18, 2025
@github-project-automation github-project-automation bot moved this to Tracking for review in Spec Core Team Workflow Nov 18, 2025
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turt2live reviewed Nov 18, 2025
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turt2live commented Nov 18, 2025 •
edited by richvdh
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MSCs proposed for Final Comment Period (FCP) should meet the requirements outlined in the checklist prior to being accepted into the spec. This checklist is a bit long, but aims to reduce the number of follow-on MSCs after a feature lands.

SCT members: please check off things you check for, and raise a concern against FCP if the checklist is incomplete. If an item doesn't apply, prefer to check it rather than remove it. Unchecking items is encouraged where applicable.

MSC authors: feel free to ask in a thread on your MSC or in the#matrix-spec:matrix.org room for clarification of any of these points.

  • Are appropriate implementation(s) specified in the MSC’s PR description?
  • Are all MSCs that this MSC depends on already accepted?
  • For each new endpoint that is introduced:
    • Have authentication requirements been specified?
    • Have rate-limiting requirements been specified?
    • Have guest access requirements been specified?
    • Are error responses specified?
      • Does each error case have a specified errcode (e.g. M_FORBIDDEN) and HTTP status code?
        • If a new errcode is introduced, is it clear that it is new?
  • Will the MSC require a new room version, and if so, has that been made clear?
    • Is the reason for a new room version clearly stated? For example, modifying the set of redacted fields changes how event IDs are calculated, thus requiring a new room version.
  • Are backwards-compatibility concerns appropriately addressed?
  • Are the endpoint conventions honoured?
    • Do HTTP endpoints use_underscores_like_this?
    • Will the endpoint return unbounded data? If so, has pagination been considered?
    • If the endpoint utilises pagination, is it consistent with the appendices?
  • An introduction exists and clearly outlines the problem being solved. Ideally, the first paragraph should be understandable by a non-technical audience.
  • All outstanding threads are resolved
    • All feedback is incorporated into the proposal text itself, either as a fix or noted as an alternative
  • While the exact sections do not need to be present, the details implied by the proposal template are covered. Namely:
    • Introduction
    • Proposal text
    • Potential issues
    • Alternatives
    • Dependencies
  • Stable identifiers are used throughout the proposal, except for the unstable prefix section
    • Unstable prefixes consider the awkward accepted-but-not-merged state
    • Chosen unstable prefixes do not pollute any global namespace (use “org.matrix.mscXXXX”, not “org.matrix”).
  • Changes have applicable Sign Off from all authors/editors/contributors
  • There is a dedicated "Security Considerations" section which detail any possible attacks/vulnerabilities this proposal may introduce, even if this is "None.". See RFC3552 for things to think about, but in particular pay attention to the OWASP Top Ten.

turt2live
turt2live approved these changes Nov 18, 2025
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lgtm - just the one comment to complete the checklist

@Half-Shot Half-Shot self-requested a review November 18, 2025 23:13
jevolk added a commit to matrix-construct/ruma that referenced this pull request Nov 19, 2025
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events: Implment MSC4380 Invite Blocking.
dc881a0 
matrix-org/matrix-spec-proposals#4380

Signed-off-by: Jason Volk <[email protected]>
jevolk added a commit to matrix-construct/ruma that referenced this pull request Nov 19, 2025
@jevolk
events: Implment MSC4380 Invite Blocking.
9d5b385 
matrix-org/matrix-spec-proposals#4380

Signed-off-by: Jason Volk <[email protected]>
@jevolk jevolk mentioned this pull request Nov 19, 2025
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jevolk added a commit to matrix-construct/ruma that referenced this pull request Nov 19, 2025
@jevolk
events: Implement MSC4380 Invite Blocking.
b451823 
matrix-org/matrix-spec-proposals#4380

Signed-off-by: Jason Volk <[email protected]>
@turt2live turt2live removed the needs-implementation This MSC does not have a qualifying implementation for the SCT to review. The MSC cannot enter FCP. label Nov 19, 2025
marwing
marwing reviewed Nov 19, 2025
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richvdh commented Nov 25, 2025

Per fbdeb55, I decided to switch from block_all: true|false to default_action: "block"|"allow", mostly to allow easier extension in future to "block"|"allow"|"ignore".

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richvdh commented Dec 2, 2025

I claim this is ready for FCP.

@mscbot fcp merge

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mscbot commented Dec 2, 2025 •
edited by uhoreg
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Team member @richvdh has proposed to merge this. The next step is review by the rest of the tagged people:

Once at least 75% of reviewers approve (and there are no outstanding concerns), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for information about what commands tagged team members can give me.

@mscbot mscbot added proposed-final-comment-period Currently awaiting signoff of a majority of team members in order to enter the final comment period. disposition-merge labels Dec 2, 2025
@richvdh richvdh moved this from Tracking for review to Ready for FCP ticks in Spec Core Team Workflow Dec 2, 2025
@turt2live turt2live added the 00-weekly-pings Tracking for weekly pings in the SCT office. 00 to make it first in the labels list. label Dec 2, 2025
@turt2live turt2live mentioned this pull request Dec 3, 2025
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uhoreg
uhoreg reviewed Dec 9, 2025
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reivilibre added a commit to element-hq/synapse that referenced this pull request Dec 11, 2025
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Merge tag 'v1.144.0' into kegan/sticky-events
9016d68 
The team has decided to deprecate and stop publishing python wheels for MacOS.
Synapse docker images will continue to work on MacOS, as will building Synapse
from source (though note this requires a Rust compiler).

Admins using the unstable [MSC2666](matrix-org/matrix-spec-proposals#2666) endpoint (`/_matrix/client/unstable/uk.half-shot.msc2666/user/mutual_rooms`),
please check [the relevant section in the upgrade notes](https://github.com/element-hq/synapse/blob/develop/docs/upgrade.md#upgrading-to-v11440) as this release contains changes
that disable that endpoint by default.

No significant changes since 1.144.0rc1.

Admins using the unstable [MSC2666](matrix-org/matrix-spec-proposals#2666) endpoint (`/_matrix/client/unstable/uk.half-shot.msc2666/user/mutual_rooms`), please check [the relevant section in the upgrade notes](https://github.com/element-hq/synapse/blob/develop/docs/upgrade.md#upgrading-to-v11440) as this release contains changes that disable that endpoint by default.

- Add experimentatal implememntation of [MSC4380](matrix-org/matrix-spec-proposals#4380) (invite blocking). ([\#19203](#19203))
- Allow restarting delayed event timeouts on workers. ([\#19207](#19207))

- Fix a bug in the database function for fetching state deltas that could result in unnecessarily long query times. ([\#18960](#18960))
- Fix v12 rooms when running with `use_frozen_dicts: True`. ([\#19235](#19235))
- Fix bug where invalid `canonical_alias` content would return 500 instead of 400. ([\#19240](#19240))
- Fix bug where `Duration` was logged incorrectly. ([\#19267](#19267))

- Document in the `--config-path` help how multiple files are merged - by merging them shallowly. ([\#19243](#19243))

- Stop building release wheels for MacOS. ([\#19225](#19225))

- Improve event filtering for Simplified Sliding Sync. ([\#17782](#17782))
- Export `SYNAPSE_SUPPORTED_COMPLEMENT_TEST_PACKAGES` environment variable from `scripts-dev/complement.sh`. ([\#19208](#19208))
- Refactor `scripts-dev/complement.sh` logic to avoid `exit` to facilitate being able to source it from other scripts (composable). ([\#19209](#19209))
- Expire sliding sync connections that are too old or have too much pending data. ([\#19211](#19211))
- Require an experimental feature flag to be enabled in order for the unstable [MSC2666](matrix-org/matrix-spec-proposals#2666) endpoint (`/_matrix/client/unstable/uk.half-shot.msc2666/user/mutual_rooms`) to be available. ([\#19219](#19219))
- Prevent changelog check CI running on @dependabot's PRs even when a human has modified the branch. ([\#19220](#19220))
- Auto-fix trailing spaces in multi-line strings and comments when running the lint script. ([\#19221](#19221))
- Move towards using a dedicated `Duration` type. ([\#19223](#19223), [\#19229](#19229))
- Improve robustness of the SQL schema linting in CI. ([\#19224](#19224))
- Add log to determine whether clients are using `/messages` as expected. ([\#19226](#19226))
- Simplify README and add ESS Getting started section. ([\#19228](#19228), [\#19259](#19259))
- Add a unit test for ensuring associated refresh tokens are erased when a device is deleted. ([\#19230](#19230))
- Prompt user to consider adding future deprecations to the changelog in release script. ([\#19239](#19239))
- Fix check of the Rust compiled code being outdated when using source checkout and `.egg-info`. ([\#19251](#19251))
- Stop building macos wheels in CI pipeline. ([\#19263](#19263))

* Bump Swatinem/rust-cache from 2.8.1 to 2.8.2. ([\#19244](#19244))
* Bump actions/checkout from 5.0.0 to 6.0.0. ([\#19213](#19213))
* Bump actions/setup-go from 6.0.0 to 6.1.0. ([\#19214](#19214))
* Bump actions/setup-python from 6.0.0 to 6.1.0. ([\#19245](#19245))
* Bump attrs from 25.3.0 to 25.4.0. ([\#19215](#19215))
* Bump docker/metadata-action from 5.9.0 to 5.10.0. ([\#19246](#19246))
* Bump http from 1.3.1 to 1.4.0. ([\#19249](#19249))
* Bump pydantic from 2.12.4 to 2.12.5. ([\#19250](#19250))
* Bump pyopenssl from 25.1.0 to 25.3.0. ([\#19248](#19248))
* Bump rpds-py from 0.28.0 to 0.29.0. ([\#19216](#19216))
* Bump rpds-py from 0.29.0 to 0.30.0. ([\#19247](#19247))
* Bump sentry-sdk from 2.44.0 to 2.46.0. ([\#19218](#19218))
* Bump types-bleach from 6.2.0.20250809 to 6.3.0.20251115. ([\#19217](#19217))
* Bump types-jsonschema from 4.25.1.20250822 to 4.25.1.20251009. ([\#19252](#19252))
dbkr
dbkr reviewed Jan 13, 2026
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proposals/4380-invite-blocking.md
* [`PUT /_matrix/federation/v1/invite/{roomId}/{eventId}`](https://spec.matrix.org/v1.15/server-server-api/#put_matrixfederationv1inviteroomideventid)
* [`PUT /_matrix/federation/v2/invite/{roomId}/{eventId}`](https://spec.matrix.org/v1.15/server-server-api/#put_matrixfederationv2inviteroomideventid)
* [`POST /_matrix/client/v3/rooms/{roomId}/invite`](https://spec.matrix.org/v1.15/client-server-api/#post_matrixclientv3roomsroomidinvite)
* [`POST /_matrix/client/v3/createRoom`](https://spec.matrix.org/v1.15/client-server-api/#post_matrixclientv3createroom)
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Presumably in this case, the room would also not be created? Also, I think this is the only endpoint that. allows inviting multiple users at once, so does it have a way to signal which matrix ID was blocked?

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Invites can only be sent after the room is created, so currently any invite blocking will result in the room being created, but some or all invites not being sent

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@richvdh richvdh Jan 13, 2026 •
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yup, there are a number of bugs around this, such as element-hq/synapse#8895 and matrix-org/matrix-spec#1951, and I don't plan to fix that today.

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00-weekly-pings Tracking for weekly pings in the SCT office. 00 to make it first in the labels list. client-server Client-Server API disposition-merge kind:core MSC which is critical to the protocol's success proposal A matrix spec change proposal proposed-final-comment-period Currently awaiting signoff of a majority of team members in order to enter the final comment period. safety

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