CVE-2026-5199

CVE-2026-5199 affects Temporal Server v1.29.0 and later, allowing a writer role user in an attacker-controlled namespace to signal, delete, or reset workflows and activities in a victim namespace on the same cluster. This vulnerability arises from a bug that permitted attackers to control the namespace name value during batch activity operations, bypassing cross-namespace validation. Exploitation requires high complexity, necessitating knowledge of victim workflow IDs and specific server configurations enabling cross-namespace authorization for internal components. The potential impact is limited to low integrity and availability of affected workflows, resulting in a CVSS score of 2.3 (LOW). There is currently no evidence of active exploitation, public exploit code, or significant community discussion regarding this vulnerability.