Merge pull request #9 from kevinbackhouse/FacebookFizz

Facebook Fizz demo

Author: jf205

ql_demos/cpp/Facebook_Fizz_CVE-2019-3560/FizzOverflow.ql

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+/**
+ * @name Fizz Overflow
+ * @description Narrowing conversions on untrusted data could enable
+ *              an attacker to trigger an integer overflow.
+ * @kind path-problem
+ * @problem.severity warning
+ */
+
+import cpp
+import semmle.code.cpp.ir.dataflow.TaintTracking
+import semmle.code.cpp.ir.IR
+import DataFlow::PathGraph
+
+/**
+ * The endianness conversion function `Endian::big()`.
+ * It is Folly's replacement for `ntohs` and `ntohl`.
+ */
+class EndianConvert extends Function {
+  EndianConvert() {
+    this.getName() = "big" and
+    this.getDeclaringType().getName().matches("Endian")
+  }
+}
+
+class Cfg extends TaintTracking::Configuration {
+  Cfg() { this = "FizzOverflowIR" }
+
+  /** Holds if `source` is a call to `Endian::big()`. */
+  override predicate isSource(DataFlow::Node source) {
+    source.(CallInstruction).getCallTarget().(FunctionInstruction).getFunctionSymbol() instanceof
+      EndianConvert
+  }
+
+  /** Hold if `sink` is a narrowing conversion. */
+  override predicate isSink(DataFlow::Node sink) {
+    sink.getResultSize() < sink.(ConvertInstruction).getUnary().getResultSize()
+  }
+}
+
+from
+  Cfg cfg, DataFlow::PathNode source, DataFlow::PathNode sink, ConvertInstruction conv,
+  Type inputType, Type outputType
+where
+  cfg.hasFlowPath(source, sink) and
+  conv = sink.getNode() and
+  inputType = conv.getUnary().getResultType() and
+  outputType = conv.getResultType()
+select sink, source, sink,
+  "Conversion of untrusted data from " + inputType + " to " + outputType + "."

ql_demos/cpp/Facebook_Fizz_CVE-2019-3560/README.md

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+# Facebook Fizz integer overflow vulnerability (CVE-2019-3560)
+
+Use [this snapshot](https://downloads.lgtm.com/snapshots/cpp/facebook/fizz/facebookincubator_fizz_cpp-srcVersion_c69ad1baf3f04620393ebadc3eedd130b74f4023-dist_odasa-lgtm-2019-01-13-f9dca2a-universal.zip) for the demo.
+
+[Fizz](https://github.com/facebookincubator/fizz) contained a remotely triggerable infinite loop. For more details about the bug, see this [blog post](https://lgtm.com/blog/facebook_fizz_CVE-2019-3560). A proof-of-concept exploit is available [here](https://github.com/Semmle/SecurityExploits/tree/446048470633bf0f8da9570d008d056dbaa28ea9/Facebook/Fizz/CVE-2019-3560).