Google Vertex AI SDK Flaw Let Attackers Hijack Model Uploads via Bucket Squatting

Google Vertex AI SDK Flaw Let Attackers Hijack Model Uploads via Bucket Squatting Swati KhandelwalJun 16, 2026Machine Learning / Cloud Security A flaw in the Google Cloud Vertex AI SDK for Python let an attacker with no access to a victim's project hijack the victim's machine learning model upload and run code inside Google's serving infrastructure. Palo Alto Networks Unit 42, which found and reported the bug through Google's bug bounty program, calls the technique "Pickle in the Middle" and said it saw no exploitation in the wild. Google has patched it; if you use the SDK, update to version 1.148.0 or later. The attacker needed only a Google Cloud project of their own and the victim's project ID, which is often public. No credentials, no phishing, no foothold in the target. The flaw was in how the SDK chose a temporary Cloud Storage bucket for model uploads. If a user did not set a bucket, the SDK generated a predictable name from the project ID and region, such as project-vertex-staging-region. It checked whether that bucket existed, but not whether the victim owned it. Because bucket names are globally unique, an attacker could create the expected bucket first in their own project. The victim's SDK would then upload the model files to the attacker's bucket. The attacker could then replace the uploaded model with a malicious one. Many Python ML models are saved with pickle or joblib, which can run code when a file is loaded. When Vertex AI later loaded the swapped model, the attacker's code executed inside the serving container. The attack depended on speed. Unit 42 measured about 2.5 seconds between the victim's upload and Vertex AI reading the file. In its proof of concept, the attacker used a Cloud Function that triggered after upload and replaced the model in 1.4 seconds, before Vertex AI read it. The payload then stole an OAuth token from the serving container's metadata server and sent it to the attacker. In Unit 42's test environment, that token was not limited to the compromised deployment. It could access other model artifacts in the same Google-managed tenant project, including a full TensorFlow model with trained weights, as well as BigQuery metadata, access lists, tenant logs, GKE cluster names, and internal container image paths. The attack worked only under specific conditions: the victim's default staging bucket did not already exist in that region, and the victim left the staging_bucket parameter unset. The first is common for a new project in Vertex AI in a region. The second depends on the developer relying on the SDK's default rather than naming their own bucket. Unit 42 reported the flaw through Google's Vulnerability Reward Program on March 5, 2026. It tested versions 1.139.0 and 1.140.0, the latest available at the time, and found both vulnerable. Google shipped an initial fix in v1.144.0 on March 31, adding a random uuid4 to the bucket name. It completed the fix in v1.148.0 on April 15, adding bucket ownership verification to block bucket squatting in Model.upload(). As of publication, neither Unit 42 nor Google's Vertex AI security bulletins list a CVE for the issue. Update to 1.148.0 or later so the ownership check is active. Also, set an explicit staging_bucket to a Cloud Storage location you control when uploading models. Because the flawed logic lives in the client SDK, check the google-cloud-aiplatform version wherever it runs, including notebooks, CI jobs, and training pipelines, not only production services. It is the second predictable-bucket-name flaw to surface in Vertex AI this year. Google patched CVE-2026-2473 in February, a separate bucket-squatting bug in Vertex AI Experiments that also allowed cross-tenant code execution, model theft, and poisoning. Unit 42's earlier work on Vertex AI's default service-agent permissions traced a related path from a deployed AI agent into customer and tenant data. Found this article interesting? Follow us on Google News, Twitter and LinkedIn to read more exclusive content we post. SHARE     Tweet Share Share SHARE  Bucket Squatting, Cloud security, cybersecurity, Google Cloud, machine learning, Model Poisoning, Python, Vertex AI ⚡ Top Stories This Week Cybersecurity Stars Awards 2026: Winners Announced Across 95 Categories Agentjacking Attack Tricks AI Coding Agents Into Running Malicious Code Chrome V8 Zero-Day CVE-2026-11645 Exploited in the Wild - Patch Now Microsoft Defender RoguePlanet Zero-Day Grants SYSTEM Access on Updated Windows Critical Splunk Enterprise Flaw Lets Attackers Run Code Without Authentication Ivanti, Fortinet, and SAP Release Patches for Multiple Critical Vulnerabilities New GreatXML Exploit Bypasses Windows BitLocker via Recovery Partition XML Files Researchers Build Self-Replicating AI Worm That Operates Entirely on Local, Open-Weight Models Over 400 Arch Linux AUR Packages Hijacked to Deploy Infostealer and eBPF Rootkit U.S. Orders Anthropic to Suspend Fable 5 and Mythos 5 Access for Foreign Nationals ThreatsDay Bulletin: Worm Code Leaked, AI Agent Phished, Claude Code Patch + 28 New Stories Microsoft Patches Record 206 Flaws, Including Three Zero-Days and Critical RCE Bugs China-Linked Hackers Backdoored Linux Login Software to Hide for Nearly a Decade Anthropic Releases Claude Fable 5, Its Most Powerful AI Yet, With Cyber Safeguards Load More ▼ ⭐ Featured Resources Have You Outgrown Your MDR? 7 Warning Signs Every CISO Should Check Get the 2026 Guide to Govern and Secure Enterprise AI Agents at Scale [Watch Demo] See Which Security Gaps Attackers Could Exploit First AI Can’t Stop Every Attack. 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