Discourse is an open-source discussion platform. Prior to versions 3.4.3 on the stable branch and 3.5.0.beta3 on the beta branch, the users limit for a DM can be bypassed, thus giving the ability to potentially create a DM with every user from a site in it. This issue has been patched in stable version 3.4.3 and beta version 3.5.0.beta3.

Discourse is an option source discussion platform. Prior to version 2.8.14 on the stable branch and version 3.0.0.beta16 on the beta and tests-passed branches, when a user requests for a password reset link email, then changes their primary email, the old reset email is still valid. When the old reset email is used to reset the password, the Discourse account's primary email would be re-linked to the old email. If the old email address is compromised or has transferred ownership, this leads to an account takeover. This is however mitigated by the SiteSetting emailtokenvalidhours which is currently 48 hours. Users should upgrade to versions 2.8.14 or 3.0.0.beta15 to receive a patch. As a workaround, lower emailtokenvalidhours as needed.

Discourse is an option source discussion platform. Prior to version 2.8.14 on the stable branch and version 3.0.0.beta16 on the beta and tests-passed branches, the number of times a user posted in an arbitrary topic is exposed to unauthorized users through the /u/username.json endpoint. The issue is patched in version 2.8.14 and 3.0.0.beta16. There is no known workaround.

Discourse is an option source discussion platform. Prior to version 2.8.14 on the stable branch and version 3.0.0.beta16 on the beta and tests-passed branches, pending post titles can be used for cross-site scripting attacks. Pending posts can be created by unprivileged users when a category has the "require moderator approval of all new topics" setting set. This vulnerability can lead to a full XSS on sites which have modified or disabled Discourse’s default Content Security Policy. A patch is available in versions 2.8.14 and 3.0.0.beta16.

Discourse is an option source discussion platform. Prior to version 2.8.14 on the stable branch and version 3.0.0.beta16 on the beta and tests-passed branches, tag descriptions, which can be updated by moderators, can be used for cross-site scripting attacks. This vulnerability can lead to a full XSS on sites which have modified or disabled Discourse’s default Content Security Policy. Versions 2.8.14 and 3.0.0.beta16 contain a patch.

Discourse is an open-source discussion platform. Prior to version 3.0.1 on the stable branch and 3.1.0.beta2 on the beta and tests-passed branches, when submitting a membership request, there is no character limit for the reason provided with the request. This could potentially allow a user to flood the database with a large amount of data. However it is unlikely this could be used as part of a DoS attack, as the paths reading back the reasons are only available to administrators. Starting in version 3.0.1 on the stable branch and 3.1.0.beta2 on the beta and tests-passed branches, a limit of 280 characters has been introduced for membership requests.

Discourse is an open-source discussion platform. Prior to version 3.0.1 on the stable branch and 3.1.0.beta2 on the beta and tests-passed branches, the contents of latest/top routes for restricted tags can be accessed by unauthorized users. This issue is patched in version 3.0.1 on the stable branch and 3.1.0.beta2 on the beta and tests-passed branches. There are no known workarounds.

Discourse is an open-source discussion platform. Prior to version 3.0.1 on the stable branch and version 3.1.0.beta2 on the beta and tests-passed branches, a malicious user can cause a regular expression denial of service using a carefully crafted user agent. This issue is patched in version 3.0.1 on the stable branch and version 3.1.0.beta2 on the beta and tests-passed branches. There are no known workarounds.

Discourse is an open-source discussion platform. Prior to version 3.0.1 on the stable branch and version 3.1.0.beta2 on the beta and tests-passed branches, someone can use the excludetag param to filter out topics and deduce which ones were using a specific hidden tag. This affects any Discourse site using hidden tags in public categories. This issue is patched in version 3.0.1 on the stable branch and version 3.1.0.beta2 on the beta and tests-passed branches. As a workaround, secure any categories that are using hidden tags, change any existing hidden tags to not include private data, or remove any hidden tags currently in use.

Discourse is an open source discussion platform. The embeddable comments can be exploited to create new topics as any user but without any clear title or content. This issue is patched in the latest stable, beta and tests-passed versions of Discourse. As a workaround, disable embeddable comments by deleting all embeddable hosts.

Discourse is an open-source messaging platform. In versions 3.0.1 and prior on the stable branch and versions 3.1.0.beta2 and prior on the beta and tests-passed branches, the count of personal messages displayed for a tag is a count of all personal messages regardless of whether the personal message is visible to a given user. As a result, any users can technically poll a sensitive tag to determine if a new personal message is created even if the user does not have access to the personal message.

In the patched versions, the count of personal messages tagged with a given tag is hidden by default. To revert to the old behaviour of displaying the count of personal messages for a given tag, an admin may enable the displaypersonalmessagestagcounts site setting.

Discourse is an open-source discussion platform. Prior to version 3.0.1 of the stable branch and version 3.1.0.beta2 of the beta and tests-passed branches, the count of topics displayed for a tag is a count of all regular topics regardless of whether the topic is in a read restricted category or not. As a result, any users can technically poll a sensitive tag to determine if a new topic is created in a category which the user does not have excess to.

In version 3.0.1 of the stable branch and version 3.1.0.beta2 of the beta and tests-passed branches, the count of topics displayed for a tag defaults to only counting regular topics which are not in read restricted categories. Staff users will continue to see a count of all topics regardless of the topic's category read restrictions.

Discourse is an open source platform for community discussion. In affected versions a maliciously crafted request from a Discourse administrator can lead to a long-running request and eventual timeout. This has the greatest potential impact in shared hosting environments where admins are untrusted. This issue has been addressed in versions 3.0.3 and 3.1.0.beta4. Users are advised to upgrade. There are no known workarounds for this vulnerability.

Discourse is an open source discussion platform. Prior to version 3.1.0.beta7 of the beta and tests-passed branches, a CSP (Content Security Policy) nonce reuse vulnerability was discovered could allow cross-site scripting (XSS) attacks to bypass CSP protection for anonymous (i.e. unauthenticated) users. There are no known XSS vectors at the moment, but should one be discovered, this vulnerability would allow the XSS attack to bypass CSP and execute successfully. This vulnerability isn't applicable to logged-in users. Version 3.1.0.beta7 contains a patch. The stable branch doesn't have this vulnerability. A workaround to prevent the vulnerability is to disable Google Tag Manager, i.e., unset the gtm container id setting.

Discourse is an open source discussion platform. Prior to version 3.0.6 of the stable branch and version 3.1.0.beta7 of the beta and tests-passed branches, more users than permitted could be created from invite links. The issue is patched in version 3.0.6 of the stable branch and version 3.1.0.beta7 of the beta and tests-passed branches. As a workaround, use restrict to email address invites.

Discourse is an open source discussion platform. Prior to version 3.0.6 of the stable branch and version 3.1.0.beta7 of the beta and tests-passed branches, a malicious user can edit a post in a topic and cause a DoS with a carefully crafted edit reason. The issue is patched in version 3.0.6 of the stable branch and version 3.1.0.beta7 of the beta and tests-passed branches. There are no known workarounds for this vulnerability.

Discourse is an open source discussion platform. Prior to version 3.0.6 of the stable branch and version 3.1.0.beta7 of the beta and tests-passed branches, a malicious user can prevent the defer queue from proceeding promptly on sites hosted in the same multisite installation. The issue is patched in version 3.0.6 of the stable branch and version 3.1.0.beta7 of the beta and tests-passed branches. There are no known workarounds for this vulnerability. Users of multisite configurations should upgrade.

Discourse is an open source discussion platform. Prior to version 3.0.6 of the stable branch and version 3.1.0.beta7 of the beta and tests-passed branches, in multiple controller actions, Discourse accepts limit params but does not impose any upper bound on the values being accepted. Without an upper bound, the software may allow arbitrary users to generate DB queries which may end up exhausting the resources on the server. The issue is patched in version 3.0.6 of the stable branch and version 3.1.0.beta7 of the beta and tests-passed branches. There are no known workarounds for this vulnerability.

Discourse is an open source discussion platform. Prior to version 3.0.6 of the stable branch and version 3.1.0.beta7 of the beta and tests-passed branches, information about restricted-visibility topic tags could be obtained by unauthorized users. The issue is patched in version 3.0.6 of the stable branch and version 3.1.0.beta7 of the beta and tests-passed branches.

Discourse is an open-source discussion platform. Prior to version 3.1.1 of the stable branch and version 3.2.0.beta1 of the beta and tests-passed branches, a malicious user could add a 2FA or security key with a carefully crafted name to their account and cause a denial of service for other users. The issue is patched in version 3.1.1 of the stable branch and version 3.2.0.beta1 of the beta and tests-passed branches. There are no known workarounds.

Discourse is an open-source discussion platform. Prior to version 3.1.1 of the stable branch and version 3.2.0.beta1 of the beta and tests-passed branches, importing a remote theme loads their assets into memory without enforcing limits for file size or number of files. The issue is patched in version 3.1.1 of the stable branch and version 3.2.0.beta1 of the beta and tests-passed branches. There are no known workarounds.

Discourse is an open-source discussion platform. Prior to version 3.1.1 of the stable branch and version 3.2.0.beta1 of the beta and tests-passed branches, a malicious admin could create extremely large icons sprites, which would then be cached in each server process. This may cause server processes to be killed and lead to downtime. The issue is patched in version 3.1.1 of the stable branch and version 3.2.0.beta1 of the beta and tests-passed branches. This is only a concern for multisite installations. No action is required when the admins are trusted.