A researcher has earned a total of 148,337 USD from Google for uncovering a set of flaws in Google Cloud’s Application Integration service that escalated into remote code execution (RCE) in Google Cloud production.
The core bug is now tracked as CVE‑2026‑2031. The researcher Arvin Shivram has publicly documented the issue under the title “StubZero: $148,337 RCE in Google Cloud Production” on BruteCat’s blog.
CVE-2026-2031 as a critical access control flaw in Google Cloud Application Integration that can enable remote code execution, carrying a CVSS score of 10.0.
Google has addressed the issue by restricting internal endpoint access, fixing IDOR weaknesses, and strengthening RPC security controls.
According to Arvin Shivram’s own write‑up on BruteCat.com, the chain began when an automated fuzzing tool flagged the internal API cloudcrmipfrontend-pa.googleapis.com for returning HTTP 200 responses on suspicious debugging endpoints.
Further probing revealed an endpoint, v1/integrationPlatform/getProtoDefinition, that would return protobuf descriptors for arbitrary internal messages and services, including YouTube and Google’s internal CRM stack.
Because Google’s internal services are heavily protobuf‑driven, this “req2proto as a service” style leak gave the attacker a near‑complete view of internal API schemas, making black‑box research far easier.
The same API surface also exposed a listQuotaQueue endpoint, which, when queried with the right parameters and X-Goog-Encode-Response-If-Executable: base64, leaked an internal workflow execution queue along with a crucial clientId value (default).
Google Cloud Production RCE Vulnerability
Armed with the leaked client ID, the researcher could create draft workflows via createDraftWorkflow in the internal Application Integration backend and began exploring tasks visible in the discovery document.
The turning point came with an internal task type called GenericStubbyTypedTaskV2, which the BruteCat article identifies as a generic wrapper around Google’s Stubby RPC framework inside Application Integration workflows.
By configuring GenericStubbyTypedTaskV2 with parameters such as serverSpec, serviceName, and serviceMethod, the attacker could trigger arbitrary Stubby RPC calls from Google’s production environment, using the privileged service identity of the integration platform.
Google’s Cloud Vulnerability Reward Program documentation classifies Stubby‑level access as RCE in the production environment because it provides broad access to internal services and data, depending on the RpcSecurityPolicy of the target.
Initially, workflow publishing was blocked by a two‑person approval requirement that prevented a single account from both editing and publishing a workflow.
The researcher explains on BruteCat.com that they bypassed this restriction by abusing an internal ACL endpoint, integrationPlatform/auth/setAcl, to add two attacker‑controlled Google accounts to the workflow ACL, using one as the requester and the other as approver.
In a subsequent collaboration with another researcher (“shrugged”), they discovered that Google’s initial mitigations were only partially deployed across backend instances behind a load balancer.
By repeatedly sending createDraftWorkflow requests until they hit a still‑vulnerable backend, they preserved the RCE path just before the fix fully propagated, a detail highlighted both in the BruteCat write‑up and in later podcast discussions (Critical Thinking – Episode 177).
Three months later, the same researcher identified a second RCE chain in the public Application Integration APIs involving insecure direct object references (IDOR) and the “test cases” feature.
The BruteCat post details how a global test case listing RPC, combined with a binary‑search filter technique, allowed reconstruction of victim integration UUIDs and cross‑tenant access to full workflow definitions, including those operated by internal Google teams.
Google’s Cloud VRP rules, as published on the official program page, describe tiered payouts for “Compromise of Google Cloud Production Environment,” with higher tiers for privileged production users and admin‑level access.
In line with this, Google awarded 60,000 USD for the first chain, 75,000 USD for the second, and an additional 13,337 USD for a lingering single‑service privilege escalation, for a combined payout of 148,337 USD.
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