CVE-2026-5199: 
Wolfi vulnerability analysis and mitigation

CVE-2026-5199 is a namespace authorization bypass vulnerability in Temporal Server that allows a writer role user in an attacker-controlled namespace to signal, delete, and reset workflows or activities in a victim namespace on the same cluster. The bug was introduced in Temporal Server v1.29.0 and affects versions >= 1.29.0 < 1.29.5 and >= 1.30.0 < 1.30.3. It was disclosed on April 1, 2026, and also impacted Temporal Cloud when attacker and victim namespaces resided on the same cell. The vulnerability carries a CVSS v4.0 base score of 2.3 (Low) (Github Advisory, v1.29.5 Release, v1.30.3 Release).

The root cause is classified as CWE-639 (Authorization Bypass Through User-Controlled Key). A bug in the batch activity code inadvertently allowed an attacker to supply an arbitrary namespace name value rather than having the server enforce its own trusted value. While the batch activity correctly validated the namespace ID, it failed to cross-check the namespace name against the worker's bound namespace, enabling per-namespace worker privileged credentials to operate on any namespace. Exploitation requires a server configuration with cross-namespace authorization enabled — such as deployment of the internal-frontend service or TLS-based authorization for internal identities — and the attacker must know or guess specific victim workflow IDs (and signal names for signal operations) (Github Advisory).

A successful exploit allows an attacker with writer role access in their own namespace to manipulate workflows and activities in a victim namespace on the same cluster, including signaling, deleting, and resetting them. This primarily affects integrity and availability — there is no confidentiality impact, as the attacker cannot read victim workflow data. The disruption of victim workflows could cause service outages or corrupt business-critical automation processes, and the impact extends to Temporal Cloud deployments where namespaces share the same cell (Github Advisory, v1.29.5 Release).

No public proof-of-concept exploit code is known to exist, and there is no evidence of in-the-wild exploitation at this time. The EPSS score is approximately 0.058% (18th percentile), indicating a low near-term exploitation probability. Exploitation is constrained by several preconditions: the attacker must hold a writer role in a namespace on the same cluster (or cell for Temporal Cloud), the server must have cross-namespace authorization configured, and the attacker must know or guess specific workflow IDs. The vulnerability is not listed in the CISA KEV catalog (Github Advisory).

1. Obtain writer role access: Acquire or create a writer role account in an attacker-controlled namespace on the target Temporal cluster (e.g., via a free trial, compromised credentials, or a legitimately provisioned account).
2. Confirm cross-namespace authorization: Verify that the target cluster has cross-namespace authorization enabled, such as through deployment of the internal-frontend service or TLS-based authorization for internal identities.
3. Enumerate victim workflow IDs: Attempt to discover or guess victim namespace workflow IDs through reconnaissance (e.g., predictable ID patterns, information leakage, or brute force).
4. Craft malicious batch activity request: Construct a batch activity API request that supplies the victim namespace name (instead of the attacker's own namespace name) while providing a valid namespace ID, exploiting the missing cross-check in the batch activity code.
5. Execute unauthorized operations: Submit the crafted request to signal (with a known signal name), delete, or reset target workflows or activities in the victim namespace using the attacker's per-namespace worker privileged credentials (Github Advisory).

• Logs: Temporal Server logs showing batch activity operations (signal, delete, reset) on workflows in a namespace that do not match the authenticated worker's bound namespace; audit entries where the namespace name in a request differs from the namespace associated with the authenticated credential.
• Behavioral: Unexpected workflow deletions, resets, or signals in a namespace originating from a worker identity associated with a different namespace; unusual batch activity API calls from low-privilege writer role accounts.
• Network: API requests to batch workflow endpoints where the namespace name parameter does not correspond to the caller's registered namespace, particularly from internal-frontend or TLS-authenticated internal service identities (Github Advisory).

Temporal has released patched versions addressing this vulnerability: upgrade to v1.29.5 (for the v1.29.x branch) or v1.30.3 (for the v1.30.x branch), both of which add namespace cross-checking in batch workflow processing. As a configuration-level workaround, restrict or disable cross-namespace authorization (e.g., avoid deploying the internal-frontend service or restrict TLS-based authorization for internal identities) until patching is feasible. Additionally, review and minimize writer role assignments to only trusted users, and monitor workflow operations for anomalous cross-namespace activity (v1.29.5 Release, v1.30.3 Release, Github Advisory).