Fix GHSA-3h7q-rfh9-xm4v

Weakness in auth chain indexing allows DoS from remote room members
through disk fill and high CPU usage.

A remote Matrix user with malicious intent, sharing a room with Synapse
instances before 1.104.1, can dispatch specially crafted events to
exploit a weakness in how the auth chain cover index is calculated. This
can induce high CPU consumption and accumulate excessive data in the
database of such instances, resulting in a denial of service.

Servers in private federations, or those that do not federate, are not
affected.

1 files changed, 1 insertions, 0 deletions

diff --git a/changelog.d/17044.misc b/changelog.d/17044.misc
new file mode 100644
index 0000000000..a1439752d3
--- /dev/null
+++ b/changelog.d/17044.misc
@@ -0,0 +1 @@
+Refactor auth chain fetching to reduce duplication.