Temporal Server EUVD-2026-97769

Requires an authenticated principal holding write permission in at least one namespace (PR:L), who then attaches a callback to the reserved temporal://internal address on a Workflow start request - that address was exempt from the component.callbacks.allowedAddresses allowlist, which is the core enabling condition. The target namespace must have Scheduler V2 schedules present; Scheduler V2 is OFF BY DEFAULT, so default deployments are not exposed, though schedules created while it was enabled remain targets even after the feature is turned off. Exploitation is further limited by the need to know the exact target namespace identifier, the schedule identifier, and the identity and timing of a currently running scheduled action (the AT:P attack requirement), which constrains this to targeted abuse rather than broad automated exploitation.

This is a moderate-severity, integrity-focused authorization flaw (CWE-639, IDOR-style) that should be treated as a targeted rather than mass-exploitation risk. The vendor CVSS 4.0 vector (AV:N/AC:L/AT:P/PR:L/UI:N) and score of 6.0 are internally consistent with the description: the attacker is network-reachable but must already hold authenticated write permission in some namespace (PR:L) and must satisfy a real attack requirement (AT:P) - knowledge of the target namespace ID, the schedule ID, and the identity and precise timing of a running action. Impact is integrity-only (VI:H) with no confidentiality (VC:N) or availability (VA:N) effect, matching the statement that no Workflow payloads or history are disclosed. No EPSS score, no CISA KEV listing, and no public exploit were provided, so there is no public exploit identified at time of analysis and no evidence of active exploitation; the AT:P requirement plus the need for insider-style namespace knowledge makes opportunistic, automatable exploitation unlikely. A significant mitigating signal is that Scheduler V2 is off by default and only namespaces holding Scheduler V2 schedules are targetable - so most deployments are not exposed. Net: a genuine but bounded issue, not a drop-everything emergency; prioritize patching for environments that have enabled Scheduler V2 (noting that previously-created schedules remain targets even after the feature is disabled).

An attacker with authenticated write access to any single low-value namespace crafts a Workflow start request that attaches a completion callback to the reserved temporal://internal address, which was exempt from the component.callbacks.allowedAddresses allowlist. Knowing a victim namespace ID, a Scheduler V2 schedule ID, and the timing of a currently running scheduled action, they submit a forged completion that the History service delivers to the component named by the token without re-authorizing them in the target namespace - causing the victim schedule to record the action as complete while its Workflow still runs (defeating a SKIP overlap policy) and feeding attacker-controlled data as the last completion result to the next run. No public exploit code is identified; the behavior and fix are confirmed only by the vendor patch diff.