CVE-2026-92812 in Server
Summary
by MITRE • 09/16/2026
decap-server contains a path traversal vulnerability in the local proxy containment guard that uses plain string prefix comparison without path separator validation. Attackers can access sibling directories whose names begin with the repository directory name to read, write, or delete files outside the intended repository root.
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Analysis
by VulDB Data Team • 09/17/2026
The decap-server application suffers from a critical path traversal vulnerability located within its local proxy containment guard mechanism. This security flaw stems from an insufficient validation of user-supplied input when resolving file paths for access control purposes. Specifically, the system employs a naive string prefix comparison to determine whether a requested resource resides within the allowed repository root directory. The implementation fails to account for path separators such as forward slashes or backslashes, which are essential components in defining hierarchical directory structures. Consequently, an attacker can manipulate the input path by appending sequences like dot-dot-slash followed by additional characters that match the beginning of the legitimate repository name. This manipulation allows the resolved absolute path to bypass the containment check and escape the designated sandboxed environment.
From a technical perspective, this vulnerability is classified under CWE-22: Improper Limitation of a Pathname to a Restricted Directory. The core issue lies in the logic used for boundary enforcement. By relying solely on string prefix matching without normalizing paths or validating path separators, the application incorrectly assumes that any file starting with the repository name's characters must be inside that directory. For instance, if the allowed root is repo-alpha, an attacker could request a resource at ../repo-beta/file.txt. If the system simply checks if the resulting absolute path starts with /path/to/repo-alpha, it might fail to detect this escape vector depending on how the prefix check is implemented relative to directory boundaries. This lack of robust path canonicalization and separator validation creates a significant security gap that undermines the integrity of the file access controls.
The operational impact of this vulnerability is severe, as it grants unauthorized actors the ability to read, write, or delete files outside the intended repository root. An attacker with network access to the decap-server instance can exploit this flaw to exfiltrate sensitive configuration files, source code from other projects hosted on the same server, or system-level data that should remain isolated. Furthermore, the capability to write arbitrary files could lead to remote code execution if the attacker can overwrite executable scripts or configuration files that are subsequently processed by the server. In scenarios where multiple repositories share a common parent directory, this vulnerability effectively breaks the multi-tenancy isolation model, allowing lateral movement between different project contexts and potentially compromising the entire hosting infrastructure.
This type of path traversal is frequently associated with ATT&CK technique T1083: File and Directory Discovery, as it enables an adversary to enumerate and access restricted files on a compromised system. The exploitation typically involves crafting specific HTTP requests that include maliciously formatted URL paths designed to traverse up the directory tree before re-entering a valid-looking path segment. Defenders should treat this as a high-severity issue requiring immediate remediation due to its direct impact on data confidentiality and integrity.
To mitigate this vulnerability, developers must implement strict input validation for all file path parameters. The most effective approach is to normalize the requested path using standard library functions that resolve symbolic links and relative components like dot-dot-slash before performing any access control checks. After normalization, the application should verify that the resulting absolute path strictly begins with the allowed repository root directory string, ensuring that a trailing slash or separator exists between the root name and the rest of the path to prevent prefix matching errors against sibling directories. Additionally, employing allowlists for permitted file extensions and restricting write operations to specific subdirectories can provide defense-in-depth layers. Regular security audits focusing on filesystem interaction logic are recommended to identify similar weaknesses in other parts of the application.