Summary
Temporal Server: attacker-controlled namespace could signal, delete, and reset workflows or activities in a victim namespace on the same cluster
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.
Impact
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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go.temporal.io/server to 1.30.3 or later; go.temporal.io/server to 1.29.5 or later
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2026-5199? CVE-2026-5199 is a low-severity security vulnerability in go.temporal.io/server (go), affecting versions >= 1.30.0-143.0, < 1.30.3. It is fixed in 1.30.3, 1.29.5.
- Which versions of go.temporal.io/server are affected by CVE-2026-5199? go.temporal.io/server (go) versions >= 1.30.0-143.0, < 1.30.3 is affected.
- Is there a fix for CVE-2026-5199? Yes. CVE-2026-5199 is fixed in 1.30.3, 1.29.5. Upgrade to this version or later.
- Is CVE-2026-5199 exploitable, and should I be worried? Whether CVE-2026-5199 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-5199 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-5199?
- Upgrade
go.temporal.io/serverto 1.30.3 or later - Upgrade
go.temporal.io/serverto 1.29.5 or later
- Upgrade