Temporal Server: attacker-controlled namespace could signal, delete, and reset workflows or activities in a victim namespace on the same cluster

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

2.3 · CVSS:4.0/AV:N/AC:H/AT:P/PR:L/UI:N/VC:N/VI:L/VA:L/SC:N/SI:L/SA:L · score source

EPSS

• CVE-2026-5199: 0.34% estimated exploitation activity in the next 30 days; percentile 26.95 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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…

Published by the source

1 Apr 2026, 18:36 UTC

Last modified by the source

21 Jul 2026, 14:59 UTC

Source last checked

26 Oct 2026, 15:27 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-xpg8-3hhp-p7w8

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# Patch Next advisory brief: CVE-2026-5199

Advisory: Temporal Server: attacker-controlled namespace could signal, delete, and reset workflows or activities in a victim namespace on the same cluster
IDs: CVE-2026-5199, GHSA-xpg8-3hhp-p7w8
Record: https://patchnext.com/advisories/cve-2026-5199 (revision 1, source checked 26 Oct 2026, 15:27 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Low (CVSS 2.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: go.temporal.io/server 1.30.3, 1.29.5. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go go.temporal.io/server: affected >= 1.30.0-143.0, < 1.30.3; < 1.29.5; fixed in 1.30.3, 1.29.5

## Suggested inspection (read-only)
- Go go.temporal.io/server: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on go.temporal.io/server.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-xpg8-3hhp-p7w8 (GitHub-reviewed advisory GHSA-xpg8-3hhp-p7w8 lists affected ranges: Go go.temporal.io/server >=1.30.0-143.0 =0 <1.29.5)

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