Tencent/WeKnora · critical

function '%s' is not allowed (dangerous prefix)

Error message

function '%s' is not allowed (dangerous prefix)

What it means

The SQL injection validator rejects any function whose name starts with a known-dangerous prefix (file_, copy_, binary_, etc.). This library parses untrusted SQL expressions before injecting them into queries, and prefixed functions can read/write files or execute binaries, so they are blocked outright. The check runs before the explicit dangerous-function blocklist and the whitelist.

Source

Thrown at internal/utils/inject.go:2208

		}
		if schemaName != "" && schemaName != "pg_catalog" {
			return fmt.Errorf("schema-qualified function calls are not allowed: %s", schemaName)
		}
	}

	// Block dangerous function prefixes
	if v.checkDangerousFuncs {
		dangerousPrefixes := []string{
			"pg_",     // All pg_* functions (pg_read_file, pg_reload_conf, pg_stat_*, etc.)
			"lo_",     // Large object functions (lo_import, lo_export, lo_from_bytea, lo_put, etc.)
			"dblink",  // Database link functions
			"file_",   // File functions
			"copy_",   // Copy functions
			"binary_", // Binary functions
		}
		for _, prefix := range dangerousPrefixes {
			if strings.HasPrefix(funcName, prefix) {
				return fmt.Errorf("function '%s' is not allowed (dangerous prefix)", funcName)
			}
		}

		// Block specific dangerous functions - comprehensive list for RCE prevention
		dangerousFunctions := map[string]bool{
			// Configuration and settings
			"current_setting": true,
			"set_config":      true,

			// XML/XPath functions (XXE risks)
			"query_to_xml":       true,
			"xpath":              true,
			"xmlparse":           true,
			"xmlroot":            true,
			"xmlelement":         true,
			"xmlforest":          true,
			"xmlconcat":          true,
			"xmlagg":             true,

View on GitHub (pinned to 988cbb0330)

Solutions

1. Remove the file_/copy_/binary_ function call and pre-load or pre-compute the data outside the injected expression
2. Use an allowed scalar function or a parameter placeholder instead of a file/binary function
3. If the operation is legitimately required, perform it via a dedicated server-side API endpoint rather than SQL injection into the expression
4. Check the dangerousPrefixes list in internal/utils/inject.go to see which prefix matched and rename nothing — never bypass it; restructure the query

Example fix

// before
expr := "copy_('data.csv')"
ValidateExpression(expr)
// after
data := loadDataFromFile("data.csv") // server-side, outside SQL
expr := fmt.Sprintf("value IN (%s)", placeholdersFrom(data))

var dangerousPrefixes = []string{"file_", "copy_", "binary_"}
func hasDangerousPrefix(fn string) bool {
    for _, p := range dangerousPrefixes {
        if strings.HasPrefix(fn, p) { return true }
    }
    return false
}
// call before submitting the expression
if hasDangerousPrefix(extractedFuncName(expr)) { return errors.New("expression uses a blocked function prefix") }

func isSafeFunctionName(name string) bool {
    return !strings.HasPrefix(name, "file_") &&
        !strings.HasPrefix(name, "copy_") &&
        !strings.HasPrefix(name, "binary_")
}

err := injector.Validate(expr)
if err != nil && strings.Contains(err.Error(), "dangerous prefix") {
    http.Error(w, "expression contains a disallowed function", http.StatusBadRequest)
    return
}

When it happens

Trigger: Calling the expression validation/injection API with a function call node whose funcName begins with one of the dangerousPrefixes entries (e.g. file_read('/etc/passwd'), copy_to(...), binary_exec(...)) in a column default, computed column, or filter expression.

Common situations: Developers porting DuckDB/postgres-flavored SQL that uses file_ or copy_ table functions to load CSVs; generated SQL from ORMs or LLMs that emit import/export helpers; users pasting data-loading snippets into filter or computed-field inputs.

Related errors

• function not allowed: %s
• join request not found
• failed to retrieve: %s
• opensearch: index not found
• 2201

AI-assisted analysis of Tencent/WeKnora@988cbb0330 (2026-09-02). Data as JSON: /api/errors/a7ef635cd8ddd10f. Report an issue: GitHub.