CVE-2026-5199 Cross Namespace Access via Batch Operation
Attackers can manipulate workflows in other namespaces if cross-namespace authorization is enabled, requiring specific IDs and names.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-5199?
CVE-2026-5199 is a low-severity missing authorization vulnerability in temporal, published on 1 Apr 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
A writer role user in an attacker-controlled namespace could signal, delete, and reset workflows or activities in a victim namespace on the same cluster. Exploitation requires the attacker to know or guess specific victim workflow ID(s) and, for signal operations, signal names. This was due to a bug introduced in Temporal Server v1.29.0 which inadvertently allowed an attacker to control the namespace name value instead of using the server's own trusted name value within the batch activity code. The batch activity validated the namespace ID but did not cross-check the namespace name against the worker's bound namespace, allowing the per-namespace worker's privileged credentials to operate on an arbitrary namespace. Exploitation requires a server configuration where internal components have cross-namespace authorization, such as deployment of the internal-frontend service or equivalent TLS-based authorization for internal identities.
This vulnerability also impacted Temporal Cloud when the attacker and victim namespaces were on the same cell, with the same preconditions as self-hosted clusters.
Weakness: CWE-639
Which versions are affected by CVE-2026-5199?
5 open source packages ship an affected version, including go.temporal.io/server.
| Package | Affected | Fixed in |
|---|---|---|
go.temporal.io/server Go | All versions | 1.29.5, 1.30.3 |
go.temporal.io/server Go | All versions | 1.29.5 |
go.temporal.io/server Go | All versions | 1.29.5 |
go.temporal.io/server Go | From 1.30.0-143.0 | 1.30.3 |
go.temporal.io/server Go | From 1.30.0-143.0 | 1.30.3 |
How do I fix CVE-2026-5199?
Upgrade go.temporal.io/server to a fixed version for your release line: 1.29.5 or 1.30.3.
Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.
Is CVE-2026-5199 being exploited?
There is no known exploitation of CVE-2026-5199 in the wild and no public exploit code.
Sources
Also known as CLEANSTART-2026-BV78886, CLEANSTART-2026-DE80520, CLEANSTART-2026-LH40285, ECHO-7744-7b2d-d504, GHSA-xpg8-3hhp-p7w8, GO-2026-5766 and 8 more.