Impact
Users could upload files with arbitrary Content-Type which would be served from the Zulip hostname with Content-Disposition: inline and no Content-Security-Policy header, allowing them to trick other users into executing arbitrary Javascript in the context of the Zulip application. Among other things, this enables session theft.
Only deployments which use the S3 storage (not the local-disk storage) are affected, and only deployments which deployed 04cf68b (merged on January 9th), which has only been in main. This vulnerability does not affect any numbered release.
Workarounds
Switching from S3 storage to the local-disk storage would nominally mitigate this, but is likely more involved than upgrading to the latest main which addresses the issue.
Patches
The vulnerability was fixed in the main branch with commit 2f6c5a8. Users running a Zulip server from the main branch should upgrade from main again to deploy this fix.
Impact
Users could upload files with arbitrary
Content-Typewhich would be served from the Zulip hostname withContent-Disposition: inlineand noContent-Security-Policyheader, allowing them to trick other users into executing arbitrary Javascript in the context of the Zulip application. Among other things, this enables session theft.Only deployments which use the S3 storage (not the local-disk storage) are affected, and only deployments which deployed 04cf68b (merged on January 9th), which has only been in
main. This vulnerability does not affect any numbered release.Workarounds
Switching from S3 storage to the local-disk storage would nominally mitigate this, but is likely more involved than upgrading to the latest
mainwhich addresses the issue.Patches
The vulnerability was fixed in the
mainbranch with commit 2f6c5a8. Users running a Zulip server from themainbranch should upgrade frommainagain to deploy this fix.