CVE-2021-37639: NULL Pointer Dereference (CWE-476)
value: TensorFlow is an end-to-end open source platform for machine learning. When restoring tensors via raw APIs, if the tensor name is not provided, TensorFlow can be tricked into dereferencing a null pointer. Alternatively, attackers can read memory outside the bounds of heap allocated data by providing some tensor names but not enough for a successful restoration. The [implementation](https://github.com/tensorflow/tensorflow/blob/47a06f40411a69c99f381495f490536972152ac0/tensorflow/core/kernels/save_restore_tensor.cc#L158-L159) retrieves the tensor list corresponding to the `tensor_name` user controlled input and immediately retrieves the tensor at the restoration index (controlled via `preferred_shard` argument). This occurs without validating that the provided list has enough values. If the list is empty this results in dereferencing a null pointer (undefined behavior). If, however, the list has some elements, if the restoration index is outside the bounds this results in heap OOB read. We have patched the issue in GitHub commit 9e82dce6e6bd1f36a57e08fa85af213e2b2f2622. The fix will be included in TensorFlow 2.6.0. We will also cherrypick this commit on TensorFlow 2.5.1, TensorFlow 2.4.3, and TensorFlow 2.3.4, as these are also affected and still in supported range.
CWE description: The product dereferences a pointer that it expects to be valid but is NULL.
CVSS v3 base score: 7.8
Published: 2021-08-12T19:15Z
Repository: https://github.com/tensorflow/tensorflow
Language: C++
Files changed: tensorflow/core/kernels/save_restore_tensor.cc
Commit date: 2021-08-02 14:34:00 -0700
Commit message: Fix NPE in restoring code.

PiperOrigin-RevId: 388303253
Change-Id: Ia8c68568cb854bca538909a182b31a618d68ce55

Diff: diff --git a/tensorflow/core/kernels/save_restore_tensor.cc b/tensorflow/core/kernels/save_restore_tensor.cc
index 953c1dfb6290b..dcbed428a5a5a 100644
--- a/tensorflow/core/kernels/save_restore_tensor.cc
+++ b/tensorflow/core/kernels/save_restore_tensor.cc
@@ -149,15 +149,22 @@ void RestoreTensor(OpKernelContext* context,
     const int64_t size = file_pattern_t.NumElements();
     OP_REQUIRES(
         context, size == 1,
         errors::InvalidArgument(
             "Input 0 (file_pattern) must be a string scalar; got a tensor of ",
-            size, "elements"));
+            size, " elements"));
   }
   const string& file_pattern = file_pattern_t.flat<tstring>()(0);
 
   const Tensor& tensor_name_t = context->input(1);
+  {
+    const int64_t size = tensor_name_t.NumElements();
+    OP_REQUIRES(context, size > restore_index,
+                errors::InvalidArgument(
+                    "Input 1 (file_pattern) must be a have at least ",
+                    restore_index + 1, " elements"));
+  }
   const string& tensor_name = tensor_name_t.flat<tstring>()(restore_index);
 
   // If we cannot find a cached reader we will allocate our own.
   std::unique_ptr<checkpoint::TensorSliceReader> allocated_reader;
 

Vulnerable code:             size, "elements"));
Fixed code:             size, " elements"));
  {
    const int64_t size = tensor_name_t.NumElements();
    OP_REQUIRES(context, size > restore_index,
                errors::InvalidArgument(
                    "Input 1 (file_pattern) must be a have at least ",
                    restore_index + 1, " elements"));
  }