CVE-2026-70481

Summary On standard channels, the message update and delete handlers accepted any caller holding write access on the channel, without checking that the caller wrote the message. Write access is the same grant a member needs in order to post, so every ordinary participant in a shared channel could rewrite or permanently delete any other participant's messages. The group and direct message branch of the same handlers enforced authorship; the standard branch did not. Preconditions Channels are disabled by default and must be enabled by an administrator (ENABLE_CHANNELS). The channel must be a standard channel; group and direct message channels are not affected. The attacker is any authenticated account with role user that holds write access on the channel, whether granted publicly, per user, or through a group. No ownership of the channel, channel manager role, or elevated role is required. Channel and message ids are returned by the listing endpoints the member can already call. Impact An ordinary member could replace the content of another member's message while the message stayed attributed to its original author, and could attach arbitrary data and meta payloads to it through the same form. The member could also permanently delete other members' messages, up to the entire visible history of the channel. This is an integrity and availability loss against other users of the channel: content can be forged under a colleague's name and records can be destroyed. It reaches no further than channels the attacker already has write access to, and it discloses nothing the attacker could not already read as a member. Pinning is unaffected and is not part of this issue. Fix Fixed in c609ec411 (#27197), released in 0.11.0. Both handlers now apply the same authorship check the group and direct message branch already used, so a non-admin caller can act only on their own messages regardless of write access. Upgrading fully resolves it, with no configuration change required. Roo

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