Claude Code WebFetch Hostname Bypass 0.2.54-2.1.163
CVE-2026-54316 Published on June 23, 2026
Claude Code: Out-of-Band Data Exfiltration via Pre-Approved HuggingFace Domain in WebFetch
Claude Code is an agentic coding tool. From 0.2.54 until 2.1.163, because the hostname huggingface.co was pre-approved as a bare hostname for the WebFetch tool, any path on that domainincluding attacker-controlled model repositorieswas auto-approved without a permission prompt or being subject to --allowedTools restrictions. An attacker able to inject untrusted content into a Claude Code context could direct it to issue WebFetch requests against attacker-controlled repository files (e.g. /resolve/main/config.json), which HuggingFace counts as downloads server-side, creating a covert out-of-band channel for encoding and exfiltrating data Claude can access such as files, environment variables, or command output. Reliably exploiting this required the ability to add untrusted content into a Claude Code context window. This vulnerability is fixed in 2.1.163.
Weakness Types
What is an Allowlist / Allow List Vulnerability?
The product implements a protection mechanism that relies on a list of inputs (or properties of inputs) that are explicitly allowed by policy because the inputs are assumed to be safe, but the list is too permissive - that is, it allows an input that is unsafe, leading to resultant weaknesses.
CVE-2026-54316 has been classified to as an Allowlist / Allow List vulnerability or weakness.
What is an Information Disclosure Vulnerability?
The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information.
CVE-2026-54316 has been classified to as an Information Disclosure vulnerability or weakness.
Covert Storage Channel
A covert storage channel transfers information through the setting of bits by one program and the reading of those bits by another. What distinguishes this case from that of ordinary operation is that the bits are used to convey encoded information. Covert storage channels occur when out-of-band data is stored in messages for the purpose of memory reuse. Covert channels are frequently classified as either storage or timing channels. Examples would include using a file intended to hold only audit information to convey user passwords--using the name of a file or perhaps status bits associated with it that can be read by all users to signal the contents of the file. Steganography, concealing information in such a manner that no one but the intended recipient knows of the existence of the message, is a good example of a covert storage channel.
Products Associated with CVE-2026-54316
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