CVE-2026-87808: SiYuan SQL Injection Vulnerability

CVE-2026-87808 Overview

CVE-2026-87808 is a read-only boundary bypass in SiYuan, an open-source personal knowledge management application. Versions at or below 3.8.1 contain an incomplete fix for the prior issue CVE-2026-32767. The POST /api/search/fullTextSearchBlock endpoint accepts caller-supplied SQL when method=2 but fails to enforce the workspace read-only boundary. An authenticated administrator can submit arbitrary SQL and gain raw read access to the blocks database, even when the workspace runs with --readonly=true. The dedicated /api/query/sql endpoint is properly blocked in read-only mode, making this a direct bypass of the intended access boundary. The issue is fixed in SiYuan v3.8.2.

Critical Impact
Authenticated administrators can bypass the SiYuan read-only workspace boundary and execute arbitrary SQL against the blocks database via /api/search/fullTextSearchBlock.

Affected Products

SiYuan versions <= 3.8.1
SiYuan workspaces launched with --readonly=true
Fixed in SiYuan v3.8.2

Discovery Timeline

2026-09-09 - CVE-2026-87808 published to NVD
2026-09-09 - Last updated in NVD database

Technical Details for CVE-2026-87808

Vulnerability Analysis

SiYuan exposes two SQL-capable HTTP endpoints. The /api/query/sql endpoint enforces read-only mode through calls to model.CheckReadonly and model.CheckReadonlyStatementInBox. The /api/search/fullTextSearchBlock endpoint accepts a method parameter, and when method=2 it forwards the caller-supplied query directly to the blocks database as SQL.

The earlier fix in commit d5e2d0bc for CVE-2026-32767 added an administrator role check for method=2. That check restricts who can call the SQL path but does not evaluate the workspace read-only state. As a result, an administrator retains an unrestricted SQL read path against the blocks database while the workspace is running with --readonly=true.

This is a broken access control weakness classified under [CWE-693] (Protection Mechanism Failure). The vulnerability enables information disclosure of any content stored in the blocks database, including note bodies, metadata, and internal identifiers that the read-only policy is designed to gate.

Root Cause

The root cause is inconsistent enforcement of the read-only boundary across SQL-capable endpoints. /api/query/sql invokes the read-only checks, while /api/search/fullTextSearchBlock with method=2 reaches model.FullTextSearchBlock without invoking model.CheckReadonly or model.CheckReadonlyStatementInBox.

Attack Vector

An authenticated administrator sends a POST request to /api/search/fullTextSearchBlock with method=2 and a query field containing arbitrary SQL. The backend executes the statement against the blocks database and returns matching rows, bypassing the read-only workspace policy that would otherwise block equivalent requests to /api/query/sql.

	}

	page, pageSize, query, paths, boxes, types, method, orderBy, groupBy := parseSearchBlockArgs(arg)

	// SQL mode requires admin privileges, consistent with /api/query/sql
	if method == 2 && !model.IsAdminRoleContext(c) {
		ret.Code = -1
		ret.Msg = "SQL search requires administrator privileges"
		return
	}

	blocks, matchedBlockCount, matchedRootCount, pageCount, docMode := model.FullTextSearchBlock(query, boxes, paths, types, method, orderBy, groupBy, page, pageSize)
	if model.IsReadOnlyRoleContext(c) {
		publishAccess := model.GetPublishAccess()

Source: SiYuan commit d5e2d0bc. This is the prior partial patch that added the administrator check but did not add read-only enforcement. The complete fix ships in v3.8.2.

Detection Methods for CVE-2026-87808

Indicators of Compromise

HTTP POST requests to /api/search/fullTextSearchBlock where the JSON body contains "method": 2.
Request bodies whose query field contains SQL keywords such as SELECT, FROM blocks, UNION, or PRAGMA rather than typical search text.
Administrator sessions issuing SQL-shaped fullTextSearchBlock calls while the workspace was launched with --readonly=true.

Detection Strategies

Inspect application access logs for /api/search/fullTextSearchBlock calls and flag payloads where method=2 originates from any client outside expected admin tooling.
Correlate SiYuan startup flags with request patterns: any method=2 SQL search that succeeds while --readonly=true is set indicates exploitation of this boundary bypass.
Alert on repeated SQL-mode search requests from a single session, which may indicate enumeration of the blocks database.

Monitoring Recommendations

Enable verbose HTTP logging on the SiYuan kernel and forward it to a central log store for retention and searching.
Monitor administrator account creation and role changes in SiYuan, since exploitation requires an authenticated admin context.
Track the deployed SiYuan version across hosts to confirm all instances are running v3.8.2 or later.

How to Mitigate CVE-2026-87808

Immediate Actions Required

Upgrade all SiYuan instances to v3.8.2 or later, which enforces the read-only boundary on /api/search/fullTextSearchBlock when method=2.
Audit existing administrator accounts and revoke any that are not strictly required for operations.
Rotate SiYuan authentication tokens and session credentials after upgrading if exposure is suspected.

Patch Information

The issue is fixed in SiYuan v3.8.2. Details are published in GitHub Security Advisory GHSA-4qwm-3p58-vh67 and the VulnCheck advisory for SiYuan. The prior partial fix is tracked in SiYuan commit d5e2d0bc.

Workarounds

Restrict network access to the SiYuan kernel HTTP interface so only trusted clients can reach /api/search/fullTextSearchBlock.
Place a reverse proxy in front of SiYuan and block POST requests to /api/search/fullTextSearchBlock whose JSON body contains "method":2 until the upgrade is applied.
Avoid running SiYuan with administrator sessions active in environments where the read-only boundary is a required control.

bash

# Example NGINX rule to block SQL-mode fullTextSearchBlock requests
location = /api/search/fullTextSearchBlock {
    if ($request_method = POST) {
        access_by_lua_block {
            ngx.req.read_body()
            local body = ngx.req.get_body_data() or ""
            if body:find('"method"%s*:%s*2') then
                ngx.exit(403)
            end
        }
    }
    proxy_pass http://siyuan_upstream;
}