Buffer Access with Incorrect Length Value

Opis

The product uses a sequential operation to read or write a buffer, but it uses an incorrect length value that causes it to access memory that is outside of the bounds of the buffer.

When the length value exceeds the size of the destination, a buffer overflow could occur.

Skutki

• Integrity, Confidentiality, Availability

  Read Memory; Modify Memory; Execute Unauthorized Code or Commands

  Buffer overflows often can be used to execute arbitrary code, which is usually outside the scope of a program's implicit security policy. This can often be used to subvert any other security service.

• Availability

  Modify Memory; DoS: Crash, Exit, or Restart; DoS: Resource Consumption (CPU)

  Buffer overflows generally lead to crashes. Other attacks leading to lack of availability are possible, including putting the program into an infinite loop.

Zapobieganie

• Requirements · Language Selection

  Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.

  For example, many languages that perform their own memory management, such as Java and Perl, are not subject to buffer overflows. Other languages, such as Ada and C#, typically provide overflow protection, but the protection can be disabled by the programmer.

  Be wary that a language's interface to native code may still be subject to overflows, even if the language itself is theoretically safe.

• Architecture and Design · Libraries or Frameworks

  Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.

  Examples include the Safe C String Library (SafeStr) by Messier and Viega [REF-57], and the Strsafe.h library from Microsoft [REF-56]. These libraries provide safer versions of overflow-prone string-handling functions.

• Operation, Build and Compilation · Environment Hardening

  Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index checking.

  D3-SFCV (Stack Frame Canary Validation) from D3FEND [REF-1334] discusses canary-based detection in detail.

  Skuteczność: Defense in Depth

• Implementation

  Consider adhering to the following rules when allocating and managing an application's memory:

  - Double check that the buffer is as large as specified.

  - When using functions that accept a number of bytes to copy, such as strncpy(), be aware that if the destination buffer size is equal to the source buffer size, it may not NULL-terminate the string.

  - Check buffer boundaries if accessing the buffer in a loop and make sure there is no danger of writing past the allocated space.

  - If necessary, truncate all input strings to a reasonable length before passing them to the copy and concatenation functions.

• Architecture and Design

  For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.

• Operation, Build and Compilation · Environment Hardening

  Run or compile the software using features or extensions that randomly arrange the positions of a program's executable and libraries in memory. Because this makes the addresses unpredictable, it can prevent an attacker from reliably jumping to exploitable code.

  Examples include Address Space Layout Randomization (ASLR) [REF-58] [REF-60] and Position-Independent Executables (PIE) [REF-64]. Imported modules may be similarly realigned if their default memory addresses conflict with other modules, in a process known as "rebasing" (for Windows) and "prelinking" (for Linux) [REF-1332] using randomly generated addresses. ASLR for libraries cannot be used in conjunction with prelink since it would require relocating the libraries at run-time, defeating the whole purpose of prelinking.

  For more information on these techniques see D3-SAOR (Segment Address Offset Randomization) from D3FEND [REF-1335].

  Skuteczność: Defense in Depth

• Operation · Environment Hardening

  Use a CPU and operating system that offers Data Execution Protection (using hardware NX or XD bits) or the equivalent techniques that simulate this feature in software, such as PaX [REF-60] [REF-61]. These techniques ensure that any instruction executed is exclusively at a memory address that is part of the code segment.

  For more information on these techniques see D3-PSEP (Process Segment Execution Prevention) from D3FEND [REF-1336].

  Skuteczność: Defense in Depth

• Architecture and Design, Operation · Environment Hardening

  Run your code using the lowest privileges that are required to accomplish the necessary tasks [REF-76]. If possible, create isolated accounts with limited privileges that are only used for a single task. That way, a successful attack will not immediately give the attacker access to the rest of the product or its environment. For example, database applications rarely need to run as the database administrator, especially in day-to-day operations.

• Architecture and Design, Operation · Sandbox or Jail

  Run the code in a "jail" or similar sandbox environment that enforces strict boundaries between the process and the operating system. This may effectively restrict which files can be accessed in a particular directory or which commands can be executed by the software.

  OS-level examples include the Unix chroot jail, AppArmor, and SELinux. In general, managed code may provide some protection. For example, java.io.FilePermission in the Java SecurityManager allows the software to specify restrictions on file operations.

  This may not be a feasible solution, and it only limits the impact to the operating system; the rest of the application may still be subject to compromise.

  Be careful to avoid CWE-243 and other weaknesses related to jails.

  Skuteczność: Limited

Przykłady podatności

• CVE-2011-1959 Chain: large length value causes buffer over-read (CWE-126)
• CVE-2011-1848 Use of packet length field to make a calculation, then copy into a fixed-size buffer
• CVE-2011-0105 Chain: retrieval of length value from an uninitialized memory location
• CVE-2011-0606 Crafted length value in document reader leads to buffer overflow
• CVE-2011-0651 SSL server overflow when the sum of multiple length fields exceeds a given value
• CVE-2010-4156 Language interpreter API function doesn't validate length argument, leading to information exposure

Słabość nadrzędna

• CWE-119 Improper Restriction of Operations within the Bounds of a Memory Buffer

Słabości podrzędne

• CWE-806 Buffer Access Using Size of Source Buffer

Kiedy powstaje

• Implementation

Dotyczy

Memory-Unsafe, C, C++, Assembly

Źródła

1. Writing Secure Code — Michael Howard, David LeBlanc, Chapter 6, "Why ACLs Are Important" Page 171, Microsoft Press, 2002
2. Address Space Layout Randomization in Windows Vista — Michael Howard
3. Limiting buffer overflows with ExecShield — Arjan van de Ven
4. PaX
5. Top 25 Series - Rank 12 - Buffer Access with Incorrect Length Value — Jason Lam, SANS Software Security Institute, 2010
6. Safe C String Library v1.0.3 — Matt Messier, John Viega
7. Using the Strsafe.h Functions — Microsoft
8. Understanding DEP as a mitigation technology part 1 — Microsoft
9. Least Privilege — Sean Barnum, Michael Gegick, 2005
10. Position Independent Executables (PIE) — Grant Murphy, Red Hat, 2012
11. Prelink and address space randomization — John Richard Moser, 2006
12. Jump Over ASLR: Attacking Branch Predictors to Bypass ASLR — Dmitry Evtyushkin, Dmitry Ponomarev, Nael Abu-Ghazaleh, 2016
13. Stack Frame Canary Validation (D3-SFCV) — D3FEND, 2023
14. Segment Address Offset Randomization (D3-SAOR) — D3FEND, 2023
15. Process Segment Execution Prevention (D3-PSEP) — D3FEND, 2023
16. Bypassing Browser Memory Protections: Setting back browser security by 10 years — Alexander Sotirov and Mark Dowd, Memory information leaks, 2008
17. AddressSanitizer