The lack thereof enables spoofing ActivityPub objects.
A malicious user could upload fake activities as attachments
and (if having access to remote search) trick local and remote
fedi instances into fetching and processing it as a valid object.
If uploads are hosted on the same domain as the instance itself,
it is possible for anyone with upload access to impersonate(!)
other users of the same instance.
If uploads are exclusively hosted on a different domain, even the most
basic check of domain of the object id and fetch url matching should
prevent impersonation. However, it may still be possible to trick
servers into accepting bogus users on the upload (sub)domain and bogus
notes attributed to such users.
Instances which later migrated to a different domain and have a
permissive redirect rule in place can still be vulnerable.
If — like Akkoma — the fetching server is overly permissive with
redirects, impersonation still works.
This was possible because Plug.Static also uses our custom
MIME type mappings used for actually authentic AP objects.
Provided external storage providers don’t somehow return ActivityStream
Content-Types on their own, instances using those are also safe against
their users being spoofed via uploads.
Akkoma instances using the OnlyMedia upload filter
cannot be exploited as a vector in this way — IF the
fetching server validates the Content-Type of
fetched objects (Akkoma itself does this already).
However, restricting uploads to only multimedia files may be a bit too
heavy-handed. Instead this commit will restrict the returned
Content-Type headers for user uploaded files to a safe subset, falling
back to generic 'application/octet-stream' for anything else.
This will also protect against non-AP payloads as e.g. used in
past frontend code injection attacks.
It’s a slight regression in user comfort, if say PDFs are uploaded,
but this trade-off seems fairly acceptable.
(Note, just excluding our own custom types would offer no protection
against non-AP payloads and bear a (perhaps small) risk of a silent
regression should MIME ever decide to add a canonical extension for
ActivityPub objects)
Now, one might expect there to be other defence mechanisms
besides Content-Type preventing counterfeits from being accepted,
like e.g. validation of the queried URL and AP ID matching.
Inserting a self-reference into our uploads is hard, but unfortunately
*oma does not verify the id in such a way and happily accepts _anything_
from the same domain (without even considering redirects).
E.g. Sharkey (and possibly other *keys) seem to attempt to guard
against this by immediately refetching the object from its ID, but
this is easily circumvented by just uploading two payloads with the
ID of one linking to the other.
Unfortunately *oma is thus _both_ a vector for spoofing and
vulnerable to those spoof payloads, resulting in an easy way
to impersonate our users.
Similar flaws exists for emoji and media proxy.
Subsequent commits will fix this by rigorously sanitising
content types in more areas, hardening our checks, improving
the default config and discouraging insecure config options.
OTP builds to 1.15
Changelog entry
Ensure policies are fully loaded
Fix :warn
use main branch for linkify
Fix warn in tests
Migrations for phoenix 1.17
Revert "Migrations for phoenix 1.17"
This reverts commit 6a3b2f15b7.
Oban upgrade
Add default empty whitelist
mix format
limit test to amd64
OTP 26 tests for 1.15
use OTP_VERSION tag
baka
just 1.15
Massive deps update
Update locale, deps
Mix format
shell????
multiline???
?
max cases 1
use assert_recieve
don't put_env in async tests
don't async conn/fs tests
mix format
FIx some uploader issues
Fix tests
Set it to `inline` because the vast majority of what's sent is multimedia
content while `attachment` would have the side-effect of triggering a
download dialog.
Closes: https://git.pleroma.social/pleroma/pleroma/-/issues/3114
Close#304.
Notes:
- This patch was made on top of Pleroma develop, so I created a separate cachex worker for request signature actions, instead of Akkoma's instance cache. If that is a merge blocker, I can attempt to move logic around for that.
- Regarding the `has_request_signatures: true -> false` state transition: I think that is a higher level thing (resetting instance state on new instance actor key) which is separate from the changes relevant to this one.
Co-authored-by: Luna <git@l4.pm>
Reviewed-on: https://akkoma.dev/AkkomaGang/akkoma/pulls/312
Co-authored-by: @luna@f.l4.pm <akkoma@l4.pm>
Co-committed-by: @luna@f.l4.pm <akkoma@l4.pm>
- Drop Expect-CT
Expect-CT has been redundant since 2018 when Certificate Transparency became mandated and required for all CAs and browsers. This header is only implemented in Chrome and is now deprecated. HTTP header analysers do not check this anymore as this is enforced by default. See https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Expect-CT
- Raise HSTS to 2 years and explicitly preload
The longer age for HSTS, the better. Header analysers prefer 2 years over 1 year now as free TLS is very common using Let's Encrypt.
For HSTS to be fully effective, you need to submit your root domain (domain.tld) to https://hstspreload.org. However, a requirement for this is the "preload" directive in Strict-Transport-Security. If you do not have "preload", it will reject your domain.
- Drop X-Download-Options
This is an IE8-era header when Adobe products used to use the IE engine for making outbound web requests to embed webpages in things like Adobe Acrobat (PDFs). Modern apps are using Microsoft Edge WebView2 or Chromium Embedded Framework. No modern browser checks or header analyser check for this.
- Set base-uri to 'none'
This is to specify the domain for relative links (`<base>` HTML tag). pleroma-fe does not use this and it's an incredibly niche tag.
I use all of these myself on my instance by rewriting the headers with zero problems. No breakage observed.
I have not compiled my Elixr changes, but I don't see why they'd break.
Co-authored-by: r3g_5z <june@terezi.dev>
Reviewed-on: https://akkoma.dev/AkkomaGang/akkoma/pulls/294
Co-authored-by: @r3g_5z@plem.sapphic.site <june@terezi.dev>
Co-committed-by: @r3g_5z@plem.sapphic.site <june@terezi.dev>
The header name was Report-To, not Reply-To.
In any case, that's now being changed to the Reporting-Endpoints HTTP
Response Header.
https://w3c.github.io/reporting/#headerhttps://github.com/w3c/reporting/issues/177
CanIUse says the Report-To header is still supported by current Chrome
and friends.
https://caniuse.com/mdn-http_headers_report-to
It doesn't have any data for the Reporting-Endpoints HTTP header, but
this article says Chrome 96 supports it.
https://web.dev/reporting-api/
(Even though that's come out one year ago, that's not compatible with
Network Error Logging which's still using the Report-To version of the
API)
Signed-off-by: Thomas Citharel <tcit@tcit.fr>
As this plug is called on every request, this should reduce load on the
database by not requiring to select on the users table every single
time, and to instead use the by-ID user cache whenever possible.
