CVE-2026-82651 in SiYuan
Summary
by MITRE • 08/30/2026
SiYuan before v3.8.1 does not apply the IsForbiddenAbsPath guard (introduced in GHSA-c8r8-95hg-mp34) to the /history/*path and /repo/diff/*path endpoints in kernel/server/serve.go. These routes require admin authentication but construct file paths independently, so an authenticated administrator can retrieve historical snapshots of sensitive files that the guard is meant to block, including data/.siyuan/publishAccess.json (plaintext publish-mode passwords) and files under data/templates/.
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Analysis
by VulDB Data Team • 08/30/2026
The vulnerability in SiYuan versions prior to 3.8.1 represents a critical authentication bypass mechanism rooted in inconsistent application of security controls across different API endpoints. Although the software introduced a protective guard known as IsForbiddenAbsPath via GitHub Security Advisory GHSA-c8r8-95hg-mp34, this safeguard was not uniformly applied to all administrative routes. Specifically, the /history/path and /repo/diff/path endpoints in kernel/server/serve.go remain vulnerable because they construct file paths independently without invoking the necessary validation logic designed to prevent directory traversal or access to restricted system files. This oversight creates a significant gap in the application's security posture, allowing an attacker who has obtained administrative credentials to bypass intended restrictions on sensitive data retrieval.
From a technical perspective, this flaw is classified under CWE-284 Improper Access Control and CWE-732 Incorrect Permission Assignment for Critical Resource. The core issue lies in the server-side logic where path construction occurs without sufficient sanitization or verification against a blacklist of forbidden absolute paths. While other endpoints correctly utilize the IsForbiddenAbsPath guard to validate that requested resources do not fall within protected directories, these specific history and diff endpoints fail to perform this check. Consequently, an authenticated administrator can manipulate the path parameters to traverse outside the intended application data directory and access arbitrary files on the underlying file system. This behavior effectively neutralizes the security boundary established by the authentication layer, as valid credentials are used to exploit a logic flaw rather than breaking encryption or bypassing login mechanisms directly.
The operational impact of this vulnerability is severe due to the high privilege level required for exploitation. An authenticated administrator can retrieve historical snapshots and diff data for sensitive configuration files that contain plaintext secrets. Most notably, the attacker can access data/.siyuan/publishAccess.json, which stores passwords used in publish mode in clear text. Additionally, files located under data/templates/ may be exposed, potentially revealing internal application structures or hardcoded credentials embedded within template definitions. The exposure of these artifacts allows for credential theft and further lateral movement within an organization's infrastructure. Since the vulnerability relies on administrative access, it poses a direct threat to organizations where insider threats are a concern or where admin accounts have been compromised through phishing or other means.
This incident aligns with MITRE ATT&CK technique T1078 Valid Accounts, as exploitation requires legitimate credentials, and T1530 Data from Local System, reflecting the unauthorized retrieval of files from the local file system. To mitigate this risk, organizations running SiYuan must immediately upgrade to version 3.8.1 or later where the IsForbiddenAbsPath guard is correctly applied to all relevant endpoints including /history/path and /repo/diff/path. Until an update can be deployed, administrators should restrict access to these specific API routes using network-level controls such as firewalls or reverse proxy rules that limit exposure to trusted internal networks only. Furthermore, it is advisable to rotate any passwords stored in publishAccess.json and review template files for embedded secrets to ensure no credentials have been compromised during the window of vulnerability.