Further details on Critical Security Update in Synapse affecting all versions prior to 0.34.1 (CVE-2019-5885)

On Thursday Jan 10th we released a Critical Security Update (Synapse, which fixes a serious security bug in Synapse 0.34.0 and earlier.  Many deployments have now upgraded to or, and we now consider it appropriate to disclose more information about the issue, to provide context and encourage the remaining affected servers to upgrade as soon as possible.

In Synapse 0.11 (Nov 2015) we added a configuration parameter called “macaroon_secret_key” which relates to our use of macaroons in authentication. Macaroons are authentication tokens which must be signed by the server which generates them, to prevent them being forged by attackers. “macaroon_secret_key” defines the key which is used for this signature, and it must therefore be kept secret to preserve the security of the server.

If the option is not set, Synapse will attempt to derive a secret key from other secrets specified in the configuration file. However, in all versions of Synapse up to and including 0.34.0, this process was faulty and a predictable value was used instead.

So if, your homeserver.yaml does not contain a macaroon_secret_key, you need to upgrade to or or Debian 0.34.0-3~bpo9+2 immediately to prevent the risk of account hijacking.

The vulnerability affects any Synapse installation which does not have a macaroon_secret_key setting. For example, the Debian and Ubuntu packages from Matrix.org, Debian and Ubuntu include a configuration file without an explicit macaroon_secret_key and must upgrade. Anyone who hasn’t updated their config since Nov 2015 or who grandfathered their config from the Debian/Ubuntu packages will likely also be affected.

We are not aware of this vulnerability being exploited in the wild, but if you are running an affected server it may still be wise to check your synapse’s user_ips database table for any unexpected access to your server’s accounts. You could also check your accounts’ device lists (shown under Settings in Riot) for unexpected devices, although this is not as reliable as an attacker could cover their tracks to remove unexpected devices.

We’ll publish a full post-mortem of the issue once we are confident that most affected servers have been upgraded.

We’d like to apologise for the inconvenience caused by this – especially to folks who upgraded since Friday who were in practice not affected.  Due to the nature of the issue we wanted to minimise details about the issue until people had a chance to upgrade. We also did not follow a planned disclosure procedure because Synapse 0.34.1 already unintentionally disclosed the existence of the bug by fixing it (causing the logout bug for affected users which led us to pull the original Synapse 0.34.1 release).

On the plus side, we are approaching the end of beta for Synapse, and going forwards hope to see much better stability and security across the board.

Thanks again for your patience,

The Matrix.org Team


This Week in Matrix 2019-01-11


Do not panic, Benpa is away, I repeat, Benpa is away. Nonetheless TWIM lives on!


Lots of spec work this week, and a shout out to anoa for his magical mscbot that provides pokes, nudges and updates on all things spec. Here’s what mscbot had to say about the past week.

Approved MSCs

[MSC 1497]: Advertising support of experimental features in the CS API
[MSC 1339]: Proposal to add a GET method to read account data
[MSC 1501]: Room version upgrades

Final Comment Period

MSC 1708: .well-known support for server name resolution
MSC 1711: X.509 certificate verification for federation connections

New and In Progress MSCs

[MSC 1794]: Federation v2 Invite API
[MSC 1796]: Improved e2e notifications
[MSC 1797]: Proposal for more granular profile error codes
[MSC 1640]: Replace event IDs with hashes
[MSC 1776]: Implementing peeking via /sync
[MSC 1777]: peeking over federation
[MSC 1779]: Proposal for Open Governance for Matrix.org (v2)

(A few may be missing as we’re still tweaking mscbot :)


Brendan had this to say:-

The Dendrite audit is over! A bunch of issues have been created on the Dendrite GitHub repository, as well as a project board in order to keep track of everything: https://github.com/matrix-org/dendrite/projects/2
There’s a fair amount of issues that have been labeled as “good first issue”, so feel free to pick them up and open pull requests if you’re looking into hacking on Dendrite! :)

And whilst we have your attention – here’s Brendan & Matthew talking through the audit in this week’s Matrix Live!


Neil says:-

This week saw the release of v0.34.0.1 and v0.34.1.1 both contain critical security updates so please update asap if you have not already done so. See here for more details, we’ll be able to share a bit more about the vuln once admins have had a chance to upgrade.

Aside from that we’ve been making progress against getting s2s api to r0 and Synapse to v1.0. Rich has been grappling with federation certificates (MSCs 1708, 1711) and Erik is pushing on with event ids as hashes MSC 1640. Meanwhile Hawkowl has been cranking out bug fixes and perf improvements and in particular taking a look at taming the user_ips table.

While Debian packager Andrewsh adds:-

latest synapse (, Python 3) in Debian, fixing CVE-2019-5885; an update to a previous release fixing this CVE uploaded to stretch-backports, using Python 2. Dependencies for a Python 3 upload approved in stretch-backports, a Python 3 upload of will be following later this week


Riot-iOS 0.7.11 has been released, with lots of bug fixes.

We have been working on e2e new screens (like key backup setup) and the re-skinning of the app.


Working to improve notifications style.

Split screen mode will be supported on next release!

Continuous autofocus on the Camera has been enabled.

Also fighting bugs on registration.


Halfshot has this to say:

Matrix-appservice-purple is being renamed to matrix-bifröst, on the basis that we now bridge to things and “burning rainbow bridge” seemed like a good description.

Other things that have happened: Performance improvements, as always. XMPP -> Matrix typing notifications XMPP -> Matrix avatars XMPP -> Matrix uploads * Matrix -> XMPP uploads (via oob)

and then follows up with this:-

As promised, we’ve got a discord bridge release out today. v0.4.0-rc1 has landed! See the change notes https://github.com/Half-Shot/matrix-appservice-discord/releases/tag/v0.4.0-rc1 . Thank you to Sorunome for doing a huge amount of work on this!

@swedneck reports that:

linuxgaming.life is now running matrix-appservice-discord v0.4.0-rc1.

Matrix.org Foundation

Matthew has a final draft of the Matrix.org Foundation governance document ready: https://github.com/matrix-org/matrix-doc/blob/matthew/msc1779/proposals/1779-open-governance.md. Comments on https://github.com/matrix-org/matrix-doc/pulls/1779 would be much appreciated!  We expect to propose merging it next week, and then incorporating it into the final Articles of the foundation.

Riot Web

Loads and loads of work happening on https://riot.im/experimental which is now where all new development is happening as we race towards launching the new design.  Highlights include:

  • All new key verification is implemented! (in olm & matrix-js-sdk).  We’re currently hooking up the UX.
  • Online key backup is pretty much finished.
  • Cross-signing is up next.
  • Redesign backlog is progressing (slightly stuck on making the RoomList resizing work nicely, but almost there)
  • Finalising the all new registration/login screens
  • …and loads of other stuff too.


kitsune reports that:

Sending files landed in master branches of libQMatrixClient and Quaternion. Finally you can send your Quaternion screenshots (as any other images, jingles, cat videos etc.) to Matrix using Quaternion ;)

Also, libQMatrixClient is available as a Conan repository, for developers who’d like to use Conan to track dependencies.

progserega reports that:

Hello to all! I am write matrix bot for bridge messages between matrix and social network vk.com (russian analog of facebook). https://github.com/progserega/MatrixVkBot

alphapapa reports that:

matrix-client.el gained a room-list buffer, which can be sorted by unread status, name, number of members, etc, and has a right-click context menu like the room-list sidebar.

matrix-client.el gained right-click context menus in the room sidebar, allowing to set room priority, notifications, etc.

The matrix-client.el git repository has moved to: https://github.com/alphapapa/matrix-client.el

Stanislav N. aka pztrn reports that:

Hey guys, joined here to post another thing that works in Matrix https://gitlab.com/pztrn/check_mk_matrix_notifications it is a script that sends check_mk notifications to Matrix. Check_mk is a “plugin” for Nagios NMS.

Cadair reports that:

It’s not my update but I saw this HomeAssistant addon for matrix (https://github.com/hassio-addons/addon-matrix) and wanted to make sure it got a shoutout on TWIM. [Seeing how nobody else has posted it in here, just on twitter etc.]

Morgan McMillian (thrrgilag) reports that:

I published v1.0.1 of the pnut-matrix bridge this week which brings public pnut.io chat rooms to the matrix network. Features include syncing of pnut.io names and avatars, matrix users ability to authorize their pnut.io accounts, and administrative controls for managing linked rooms. Project can be found at https://gitlab.dreamfall.space/thrrgilag/pnut-matrix and discussion is at #pnut-matrix:monkeystew.net

MMJD reports that:

ma1uta’s MXToot deserves mention in the blog, and in https://matrix.org/docs/projects/try-matrix-now.html . People should not be wanting of Twitter over Decentralized-Federated F(L)OSS feeds in their Matrix room.

uforia reports that:

in the koma project, the desktop client continuum now does a full sync when the user account doesn’t seem to have joined any chat rooms, this way, it can recover from some disk IO errors, or more commonly, unclean shutdowns. A ca-certificates issue with Java 11 on Debian stable was found while running a bot on a headless server, more details and the solution is in the README

vabd reports that:

Our first specs proposal of 2019 just landed in the form of SCS #16, which specifies the data/event structure for trust authorities. This is a big step as TAs play a key role in Informo’s trust/reputation system!

In the meantime, we’ve also opened SCS #19, which proposes a rework of the specs’ introduction with the idea to give newcomers a more accessible and immediate way to figure out what Informo is about, and give them some starting points so they can dive deeper into it if interested. It’s a rather small one and we’d love people to give it a look so we can aim for the most newcomer-friendly version possible

We’ve also just opened SCS #21 which specifies a way for a source to change the Matrix user it uses to publish articles (e.g. if it was previously using a server managed by non trustworthy people). As with all of our proposals introducing changes in behaviour, it’s open for people to share their comments on it for the next 7 days.

Maximus reports that:

The first alpha release for mxisd v1.3.0 has been released with already major performance improvements. Early testing and reporting about success/failure would be very much appreciated as v1.3.0 will break backward compatbility. We have been running it on our own servers for about a week now and feels really good and stable.

Friedger Müffke reports that:

I just launched OI Chat, a matrix service dedicated to Blockstack users (https://www.producthunt.com/posts/oi-chat).

It is a home server that does not rely on any passwords but on cryptography and user-owned storage

This is a first step towards login with private/public keys as suggested in MSC1768

OI Chat uses one-time logins to verify the ownership of a username that can only be created by the user if they control the blockstack account.

…and that’s all this week, folks!  Your normal hand-crafted artisanal benpa confectionery will be back next week.

Critical Security Update: Synapse

After releasing Synapse v0.34.1, we have become aware of a security vulnerability affecting all previous versions (CVE-2019-5885). v0.34.1 closed the vulnerability but, in some cases, caused users to be logged out of their clients, so we do not recommend 0.34.1 for production use.

Today we release two mitigating versions v0.34.0.1 and v0.34.1.1. Both versions close the vulnerability and will not cause users to be logged out. All installations should be upgraded to one or other immediately.

  • Admins who would otherwise upgrade to v0.34.1 (or those that have already done so) should upgrade to v0.34.1.1.
  • Admins on v0.34.0, who do not wish to bring in new non-security related behaviour, should upgrade to v0.34.0.1.

You can get the new updates for v0.34.0.1 and v0.34.1.1 here or any of the sources mentioned at https://github.com/matrix-org/synapse. Note, Synapse is now available from PyPI, pick it up here. See also our Synapse installation guide page.

We will publish more details of the vulnerability once admins have had a chance to upgrade. To our knowledge the vulnerability has not been exploited in the wild.

Many thanks for your patience, we are moving ever closer to Synapse reaching v1.0, and fixes like this one edge us ever closer.

Thanks also to the package maintainers who have coordinated with us to ensure distro packages are available for a speedy upgrade!


Porting Synapse to Python 3

Matrix’s reference homeserver, Synapse, is written in Python and uses the Twisted networking framework to power its bitslinging across the Internet. The Python version used has been strictly Python 2.7, the last supported version of Python 2, but as of this week that changes! Since Twisted and our other upstream dependencies now support the newest version of Python, Python 3, we are now able to finish the jump and port Synapse to use it by default. The port has been done in a backwards compatible way, written in a subset of Python that is usable in both Python 2 and Python 3, meaning your existing Synapse installs still work on Python 2, while preparing us for a Python 3 future.

Why port?

Porting Synapse to Python 3 prepares Synapse for a post-Python 2 world, currently scheduled for 2020. After the 1st of January in 2020, Python 2 will no longer be supported by the core Python developers and no bugfixes (even critical security ones) will be issued. As the security of software depends very much on the runtime and libraries it is running on top of, this means that by then all Python 2 software in use should have moved to Python 3 or other runtimes.

The Python 3 port has benefits other than just preparing for the End of Life of Python 2.7. Successive versions of Python 3 have improved the standard library, provided newer and clearer syntax for asynchronous code, added opt-in static typing to reduce bugs, and contained incremental performance and memory management improvements. These features, once Synapse stops supporting Python 2, can then be fully utilised to make Synapse’s codebase clearer and more performant. One bonus that we get immediately, though, is Python 3’s memory compaction of Unicode strings. Rather than storing as UCS-2/UTF-16 or UCS-4/UTF-32, it will instead store it in the smallest possible representation giving a 50%-75% memory improvement for strings only containing Latin-1 characters, such as nearly all dictionary keys, hashes, IDs, and a large proportion of messages being processed from English speaking countries. Non-English text will also see a memory improvement, as it can be commonly stored in only two bytes instead of the four in a UCS-4 “wide” Python 2 build.

Editor’s note: If you were wondering how this fits in with Dendrite (the next-gen golang homeserver): our plan is to use Synapse as the reference homeserver for all the current work going on with landing a 1.0 release of the Matrix spec: it makes no sense to try to iterate and converge on 1.0 on both Synapse and Dendrite in parallel. In order to prove that the 1.0 spec is indeed fit for purpose we then also need Synapse to exit beta and hit a 1.0 too, hence the investment to get it there. It’s worth noting that over the last year we’ve been plugging away solidly improving Synapse in general (especially given the increasing number of high-profile deployments out there), so we’re committed to getting Synapse to a formal production grade release and supporting it in the long term. Meanwhile, Dendrite development is still progressing – currently acting as a place to experiment with more radical blue-sky architectural changes, especially in low-footprint or even clientside homeservers. We expect it to catch up with Synapse once 1.0 is out the door; and meanwhile Synapse is increasingly benefiting from performance work inspired by Dendrite.

When will the port be released?

The port is has been released in a “production ready” form in Synapse 0.34.0, supporting Python 3.5, 3.6, and 3.7. This will work on installations with and without workers.

What’s it like in the real world?

Beta testers of the Python 3 port have reported lower memory usage, including lower memory “spikes” and slower memory growth. You can see this demonstrated on matrix.org:

See 10/15, ~20:00 for the Python 3 migration. This is on some of the Synchrotrons on matrix.org.

See ~11/8 for the Python 3 migration. This is on the Synapse master on matrix.org.

We have also noticed some better CPU utilisation:

See 21:30 for the migration of federation reader 1, and 21:55 for the others. The federation reader is a particular pathological case, where the replacement of lists with iterators internally on Python 3 has given us some big boosts.

See 10/15, 4:00.The CPU utilisation has gone down on synchrotron 1 after the Python 3 migration, but not as dramatically as the federation reader. Synchrotron 3 was migrated a few days later.

As some extra data-points, my personal HS consumes about 300MB now at initial start, and grows to approximately 800MB — under Python 2 the growth would be near-immediate to roughly 1.4GB.

Where to from here?

Python 2 is still a supported platform for running Synapse for the time being. We plan on ending mainstream support on 1st April 2019, where upon Python 3.5+ will be the only officially supported platform. Additionally, we will give notice ahead of time once we are ready to remove Python 2.7 compatibility from the codebase (which will be no sooner than 1st April). Although slightly inconvenient, we hope that this gives our users and integrators adequate time to migrate, whilst giving us the flexibility to use modern Python features and make Synapse a better piece of software to help power the Matrix community.

How can I try it?

The port is compatible with existing homeservers and configurations, so if you install Synapse inside a Python 3 virtualenv, you can run it from there. Of course, this differs based on your installation method, operating system, and what version of Python 3 you wish to use. Full upgrade notes live here but if you’re having problems or want to discuss specific packagings of Synapse please come ask in #synapse:matrix.org.


Many thanks go to fellow Synapse developers Erik and Rich for code review, as well as community contributors such as notafile and krombel for laying the foundations many months ago allowing this port to happen. Without them, this wouldn’t have happened.

Happy Matrixing,

Amber Brown (hawkowl)

Synapse 0.34.0 released!

Folks this is a big day for us at Matrix Towers, because today we release 0.34.0.

The big news for 0.34.0 is that we now recommend Python 3 for production use and have been running matrix.org under Python 3 for the past month.

Performance improvements have been marked, in some contexts we have seen 50% reductions in RAM and CPU usage. Here are some illustrative graphs to get you going but look out for a dedicated post delving into much more detail on the port. You can also see a Matrix Live interview with the project lead Amber (hawkowl) here.

Matrix.org federation reader workers, the big drops signify roll over to python 3

Synapse master on matrix.org, again the drop in RAM signifies the roll over to python 3

Many thanks to Amber for leading the effort, Rich and Erik for providing support as well as Notafile and Krombel from the community for pushing this effort right from the early days of the project.

If that wasn’t enough, 0.34.0 also all the usual bug fixes and perf improvements. In particular the media repository now no longer fails to decode UTF-8 filenames when downloading remote media and auto joining rooms now work on servers with consent requirements enabled.

As ever, you can get the new update here or any of the sources mentioned at https://github.com/matrix-org/synapse. Note, Synapse is now available from PyPI, pick it up here. Also, check out our new Synapse installation guide page.

In particular, if you want to run Synapse 0.34.0 on Python 3 take a look at the upgrade notes.


Synapse 0.34.0 changelog

Synapse 0.34.0 is the first release to fully support Python 3. Synapse will now run on Python versions 3.5 or 3.6 (as well as 2.7). Support for Python 3.7 remains experimental.

We recommend upgrading to Python 3, but make sure to read the upgrade notes when doing so.


  • Add ‘sandbox’ to CSP for media reprository (#4284)
  • Make the new landing page prettier. (#4294)
  • Fix deleting E2E room keys when using old SQLite versions. (#4295)
  • Add a welcome page for the client API port. Credit to @krombel! (#4289)
  • Remove Matrix console from the default distribution (#4290)
  • Add option to track MAU stats (but not limit people) (#3830)
  • Add an option to enable recording IPs for appservice users (#3831)
  • Rename login type m.login.cas to m.login.sso (#4220)
  • Add an option to disable search for homeservers that may not be interested in it. (#4230)


  • Pushrules can now again be made with non-ASCII rule IDs. (#4165)
  • The media repository now no longer fails to decode UTF-8 filenames when downloading remote media. (#4176)
  • URL previews now correctly decode non-UTF-8 text if the header contains a <meta http-equiv="Content-Type" header. (#4183)
  • Fix an issue where public consent URLs had two slashes. (#4192)
  • Fallback auth now accepts the session parameter on Python 3. (#4197)
  • Remove riot.im from the list of trusted Identity Servers in the default configuration (#4207)
  • fix start up failure when mau_limit_reserved_threepids set and db is postgres (#4211)
  • Fix auto join failures for servers that require user consent (#4223)
  • Fix exception caused by non-ascii event IDs (#4241)
  • Pushers can now be unsubscribed from on Python 3. (#4250)
  • Fix UnicodeDecodeError when postgres is configured to give non-English errors (#4253)

Internal Changes

  • Debian packages utilising a virtualenv with bundled dependencies can now be built. (#4212)
  • Disable pager when running git-show in CI (#4291)
  • A coveragerc file has been added. (#4180)
  • Add a GitHub pull request template and add multiple issue templates (#4182)
  • Update README to reflect the fact that #1491 is fixed (#4188)
  • Run the AS senders as background processes to fix warnings (#4189)
  • Add some diagnostics to the tests to detect logcontext problems (#4190)
  • Add missing jpeg package prerequisite for OpenBSD in README. (#4193)
  • Add a note saying you need to manually reclaim disk space after using the Purge History API (#4200)
  • More logcontext checking in unittests (#4205)
  • Ignore __pycache__ directories in the database schema folder (#4214)
  • Add note to UPGRADE.rst about removing riot.im from list of trusted identity servers (#4224)
  • Added automated coverage reporting to CI. (#4225)
  • Garbage-collect after each unit test to fix logcontext leaks (#4227)
  • add more detail to logging regarding “More than one row matched” error (#4234)
  • Drop sent_transactions table (#4244)
  • Add a basic .editorconfig (#4257)
  • Update README.rst and UPGRADE.rst for Python 3. (#4260)
  • Remove obsolete verbose and log_file settings from homeserver.yaml for Docker image. (#4261)