CVE-2026-101998 in Sandboxes
Summary
by MITRE • 10/08/2026
Docker Sandboxes could fail open while masking credentials in protected proxy responses. When a response-body read returned data together with an error, affected handlers could forward unmasked bytes. Code inside an authorized sandbox could use this to recover host-managed OAuth access and refresh tokens or a derived Anthropic API key intended to remain outside the sandbox.
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Analysis
by VulDB Data Team • 10/08/2026
The vulnerability described represents a critical security flaw within Docker Sandboxes that compromises the integrity of credential isolation mechanisms, specifically in the context of protected proxy responses. This issue stems from an improper error handling routine where the system fails open when processing response bodies that contain both valid data and associated errors. In standard secure programming practices, any operation resulting in an error state should trigger a fail-secure mechanism, ensuring that no partial or potentially sensitive information is exposed to untrusted contexts. However, in this specific implementation, handlers were designed to forward the bytes read from the response body even when an error condition was detected during the reading process. This behavior creates a side-channel through which masked credentials can be inadvertently leaked because the masking logic likely only applies to successful reads or assumes that errors do not occur mid-stream.
From a technical perspective, this flaw allows code executing within an authorized sandbox environment to recover host-managed OAuth access and refresh tokens as well as derived Anthropic API keys. These credentials are intended to remain strictly outside the sandbox boundary to prevent unauthorized usage by potentially compromised containerized applications or malicious actors who have gained foothold inside the sandbox. The ability to extract these tokens effectively breaks the trust model of the virtualization layer, granting the attacker privileges equivalent to those held by the host service managing the proxies. This is particularly dangerous because OAuth refresh and access tokens often provide long-lived access to sensitive APIs and user data, while API keys can be used to consume significant resources or exfiltrate proprietary information without further authentication checks.
The operational impact of this vulnerability is severe, as it undermines the fundamental principle of least privilege enforced by containerization technologies like Docker. An attacker who exploits this flaw does not need to break out of the sandbox in a traditional sense but rather leverages legitimate access within the sandbox to steal high-value credentials from the host environment. This can lead to unauthorized access to external services, data breaches involving user information protected by OAuth flows, and potential financial loss through abuse of API quotas or services billed via Anthropic keys. Furthermore, because the vulnerability involves masking failures, it may evade standard logging mechanisms that rely on detecting obvious authentication errors rather than subtle credential leakage patterns.
This issue aligns with CWE-209, which describes an information exposure through an error message where sensitive details are revealed to attackers in a format they can exploit. It also relates closely to CWE-798, the use of hardcoded credentials or improper handling of secrets, as it results in the unintended disclosure of secret material that should have been strictly isolated. In terms of MITRE ATT&CK framework tactics, this vulnerability facilitates Credential Access through techniques such as OS Credential Dumping if interpreted broadly within container contexts, but more accurately maps to Steal Application Access Tokens and potentially Exfiltration Over C2 Channels if the stolen tokens are used for further lateral movement or data theft.
Mitigation strategies must focus on correcting the error handling logic in the proxy response handlers. The system should be updated to ensure that any read operation resulting in an error does not return partial body content, especially when masking is involved. Implementing strict fail-secure defaults where errors result in empty responses or explicit failure codes without payload data will prevent the leakage of masked credentials. Additionally, developers should implement comprehensive logging and monitoring for unusual patterns in proxy response handling to detect potential exploitation attempts. Regular security audits focusing on edge cases in input/output processing are essential to identify similar flaws in other components that handle sensitive data under error conditions.