MSO.DLL in Microsoft Office 2000, Office XP (2002), and Office 2003 allows user-assisted attackers to cause a denial of service and execute arbitrary code via multiple attack vectors, as originally demonstrated using a crafted document record with a malformed string, as demonstrated by replacing a certain 01 00 00 00 byte sequence with an FF FF FF FF byte sequence, possibly causing an invalid array index, in (1) an Excel .xls document, which triggers an access violation in ole32.dll; (2) an Excel .xlw document, which triggers an access violation in excel.exe; (3) a Word document, which triggers an access violation in mso.dll in winword.exe; and (4) a PowerPoint document, which triggers an access violation in powerpnt.txt. NOTE: after the initial disclosure, this issue was demonstrated by triggering an integer overflow using an inconsistent size for a Unicode Sheet Name string.
Weakness
The product constructs all or part of a code segment using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the syntax or behavior of the intended code segment.
Affected Software
| Name |
Vendor |
Start Version |
End Version |
| Office |
Microsoft |
* |
* |
| Office |
Microsoft |
2000 (including) |
2000 (including) |
| Office |
Microsoft |
2000-sp1 (including) |
2000-sp1 (including) |
| Office |
Microsoft |
2000-sp3 (including) |
2000-sp3 (including) |
| Office |
Microsoft |
2003 (including) |
2003 (including) |
| Office |
Microsoft |
2003-sp1 (including) |
2003-sp1 (including) |
| Office |
Microsoft |
2003-sp2 (including) |
2003-sp2 (including) |
| Office |
Microsoft |
2004 (including) |
2004 (including) |
| Office |
Microsoft |
v.x (including) |
v.x (including) |
| Office |
Microsoft |
xp-sp1 (including) |
xp-sp1 (including) |
| Office |
Microsoft |
xp-sp2 (including) |
xp-sp2 (including) |
| Office |
Microsoft |
xp-sp3 (including) |
xp-sp3 (including) |
Potential Mitigations
- Run your code in a “jail” or similar sandbox environment that enforces strict boundaries between the process and the operating system. This may effectively restrict which code can be executed by your product.
- Examples include the Unix chroot jail and AppArmor. In general, managed code may provide some protection.
- This may not be a feasible solution, and it only limits the impact to the operating system; the rest of your application may still be subject to compromise.
- Be careful to avoid CWE-243 and other weaknesses related to jails.
- Assume all input is malicious. Use an “accept known good” input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
- When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, “boat” may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as “red” or “blue.”
- Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code’s environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
- To reduce the likelihood of code injection, use stringent allowlists that limit which constructs are allowed. If you are dynamically constructing code that invokes a function, then verifying that the input is alphanumeric might be insufficient. An attacker might still be able to reference a dangerous function that you did not intend to allow, such as system(), exec(), or exit().
- For Python programs, it is frequently encouraged to use the ast.literal_eval() function instead of eval, since it is intentionally designed to avoid executing code. However, an adversary could still cause excessive memory or stack consumption via deeply nested structures [REF-1372], so the python documentation discourages use of ast.literal_eval() on untrusted data [REF-1373].
References