CVE-2015-2313 (published 2017-08-09T18:29Z)

Sandstorm Cap\'n Proto before 0.4.1.1 and 0.5.x before 0.5.1.2, when an application invokes the totalSize method on an object reader, allows remote peers to cause a denial of service (CPU consumption) via a crafted small message, which triggers a "tight" for loop.  NOTE: this vulnerability exists because of an incomplete fix for CVE-2015-2312.

Severity: HIGH
CVSS v2 base score: 7.8 (AV:N/AC:L/Au:N/C:N/I:N/A:C)
CVSS v3 base score: 7.5, HIGH (CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)

Weakness information:
cwe_id: CWE-400
cwe_name: Uncontrolled Resource Consumption
description: The product does not properly control the allocation and maintenance of a limited resource, thereby enabling an actor to influence the amount of resources consumed, eventually leading to the exhaustion of available resources.
extended_description: 
            Limited resources include memory, file system storage, database connection pool entries, and CPU. If an attacker can trigger the allocation of these limited resources, but the number or size of the resources is not controlled, then the attacker could cause a denial of service that consumes all available resources. This would prevent valid users from accessing the product, and it could potentially have an impact on the surrounding environment. For example, a memory exhaustion attack against an application could slow down the application as well as its host operating system.
            There are at least three distinct scenarios which can commonly lead to resource exhaustion:
               
                  Lack of throttling for the number of allocated resources
                  Losing all references to a resource before reaching the shutdown stage
                  Not closing/returning a resource after processing
               
            Resource exhaustion problems are often result due to an incorrect implementation of the following situations:
               
                  Error conditions and other exceptional circumstances.
                  Confusion over which part of the program is responsible for releasing the resource.
               
         
         

Fix information:
repo_url: https://github.com/capnproto/capnproto
commit_details: repo_url: https://github.com/capnproto/capnproto
author: Kenton Varda
author_date: 2015-03-05 10:27:29-08:00
msg: SECURITY: Additional CPU amplification case.

Unfortunately, commit 104870608fde3c698483fdef6b97f093fc15685d missed a case of CPU amplification via struct lists with zero-sized elements.

See advisory: https://github.com/sandstorm-io/capnproto/blob/master/security-advisories/2015-03-05-0-c++-addl-cpu-amplification.md
repository: repo_url: https://github.com/capnproto/capnproto
repo_name: capnproto/capnproto
description: Cap'n Proto serialization/RPC system - core tools and C++ library
repo_language: C++
owner: capnproto
file_changes: filename: encoding-test.c++
change_type: ModificationType.MODIFY
diff: @@ -1427,17 +1427,24 @@ TEST(Encoding, VoidListAmplification) {
 }
 
 TEST(Encoding, EmptyStructListAmplification) {
-  MallocMessageBuilder builder;
-  builder.initRoot<test::TestAnyPointer>().getAnyPointerField()
-      .initAs<List<test::TestEmptyStruct>>(1u << 28);
+  MallocMessageBuilder builder(1024);
+  auto listList = builder.initRoot<test::TestAnyPointer>().getAnyPointerField()
+      .initAs<List<List<test::TestEmptyStruct>>>(500);
+
+  for (uint i = 0; i < listList.size(); i++) {
+    listList.init(i, 1u << 28);
+  }
 
   auto segments = builder.getSegmentsForOutput();
-  EXPECT_EQ(1, segments.size());
-  EXPECT_LT(segments[0].size(), 16);  // quite small for such a big list!
+  ASSERT_EQ(1, segments.size());
 
   SegmentArrayMessageReader reader(builder.getSegmentsForOutput());
-  auto root = reader.getRoot<test::TestAnyPointer>().getAnyPointerField();
-  EXPECT_NONFATAL_FAILURE(root.getAs<List<TestAllTypes>>());
+  auto root = reader.getRoot<test::TestAnyPointer>();
+  auto listListReader = root.getAnyPointerField().getAs<List<List<TestAllTypes>>>();
+  EXPECT_NONFATAL_FAILURE(listListReader[0]);
+  EXPECT_NONFATAL_FAILURE(listListReader[10]);
+
+  EXPECT_EQ(segments[0].size() - 1, root.totalSize().wordCount);
 }
 
 TEST(Encoding, Constants) {

programming_language: C++
filename: layout.c++
change_type: ModificationType.MODIFY
diff: @@ -555,14 +555,16 @@ struct WireHelpers {
             WordCount dataSize = elementTag->structRef.dataSize.get();
             WirePointerCount pointerCount = elementTag->structRef.ptrCount.get();
 
-            word* pos = ptr + POINTER_SIZE_IN_WORDS;
             uint count = elementTag->inlineCompositeListElementCount() / ELEMENTS;
-            for (uint i = 0; i < count; i++) {
-              pos += dataSize;
-
-              for (uint j = 0; j < pointerCount / POINTERS; j++) {
-                zeroObject(segment, reinterpret_cast<WirePointer*>(pos));
-                pos += POINTER_SIZE_IN_WORDS;
+            if (pointerCount > 0 * POINTERS) {
+              word* pos = ptr + POINTER_SIZE_IN_WORDS;
+              for (uint i = 0; i < count; i++) {
+                pos += dataSize;
+
+                for (uint j = 0; j < pointerCount / POINTERS; j++) {
+                  zeroObject(segment, reinterpret_cast<WirePointer*>(pos));
+                  pos += POINTER_SIZE_IN_WORDS;
+                }
               }
             }
 
@@ -680,8 +682,6 @@ struct WireHelpers {
               return result;
             }
 
-            result.wordCount += wordCount + POINTER_SIZE_IN_WORDS;
-
             const WirePointer* elementTag = reinterpret_cast<const WirePointer*>(ptr);
             ElementCount count = elementTag->inlineCompositeListElementCount();
 
@@ -690,23 +690,29 @@ struct WireHelpers {
               return result;
             }
 
-            KJ_REQUIRE(elementTag->structRef.wordSize() / ELEMENTS *
-                       ElementCount64(count) <= wordCount,
+            auto actualSize = elementTag->structRef.wordSize() / ELEMENTS * ElementCount64(count);
+            KJ_REQUIRE(actualSize <= wordCount,
                        "Struct list pointer's elements overran size.") {
               return result;
             }
 
+            // We count the actual size rather than the claimed word count because that's what
+            // we'll end up with if we make a copy.
+            result.wordCount += actualSize + POINTER_SIZE_IN_WORDS;
+
             WordCount dataSize = elementTag->structRef.dataSize.get();
             WirePointerCount pointerCount = elementTag->structRef.ptrCount.get();
 
-            const word* pos = ptr + POINTER_SIZE_IN_WORDS;
-            for (uint i = 0; i < count / ELEMENTS; i++) {
-              pos += dataSize;
+            if (pointerCount > 0 * POINTERS) {
+              const word* pos = ptr + POINTER_SIZE_IN_WORDS;
+              for (uint i = 0; i < count / ELEMENTS; i++) {
+                pos += dataSize;
 
-              for (uint j = 0; j < pointerCount / POINTERS; j++) {
-                result += totalSize(segment, reinterpret_cast<const WirePointer*>(pos),
-                                    nestingLimit);
-                pos += POINTER_SIZE_IN_WORDS;
+                for (uint j = 0; j < pointerCount / POINTERS; j++) {
+                  result += totalSize(segment, reinterpret_cast<const WirePointer*>(pos),
+                                      nestingLimit);
+                  pos += POINTER_SIZE_IN_WORDS;
+                }
               }
             }
             break;

programming_language: C++