CVE-2024-30266 (published 2024-04-04T16:15Z)

wasmtime is a runtime for WebAssembly. The 19.0.0 release of Wasmtime contains a regression introduced during its development which can lead to a guest WebAssembly module causing a panic in the host runtime. A valid WebAssembly module, when executed at runtime, may cause this panic. This vulnerability has been patched in version 19.0.1.


Weakness information:
cwe_id: NVD-CWE-noinfo
cwe_name: Insufficient Information
description: There is insufficient information about the issue to classify it; details are unkown or unspecified.
extended_description: Insufficient Information

Fix information:
repo_url: https://github.com/bytecodealliance/wasmtime
commit_details: repo_url: https://github.com/bytecodealliance/wasmtime
author: Alex Crichton
author_date: 2024-04-02 10:56:49-05:00
msg: Fix a panic using tables with the wrong type (#8283)

This commit fixes an accidental issue introduced in #8018 where using an
element segment which had been dropped with an `externref` table would
cause a panic. The panic happened due to an assertion that tables are
being used with the right type of item and that was being mismatched.
The underlying issue was that dropped element segments are modeled as an
empty element segment but the empty element segment was using the
"functions" encoding as opposed to the "expressions" encoding. This
meant that code later assumed that due to the use of functions the table
must be a table-of-functions, but this was not correct for
externref-based tables.

The fix in this commit is to instead model the encoding as an
"expressions" list which means that the table type is dispatched on to
call the appropriate initializer.

There is no memory safety issue with this mistake as the assertion was
specifically targetted at preventing memory safety. This does, however,
enable any WebAssembly module to panic a host.

Closes #8281
repository: repo_url: https://github.com/bytecodealliance/wasmtime
repo_name: bytecodealliance/wasmtime
description: A fast and secure runtime for WebAssembly
repo_language: Rust
owner: bytecodealliance
file_changes: filename: instance.rs
change_type: ModificationType.MODIFY
diff: @@ -801,7 +801,12 @@ impl Instance {
         // disconnected from the lifetime of `self`.
         let module = self.module().clone();
 
-        let empty = TableSegmentElements::Functions(Box::new([]));
+        // NB: fall back to an expressions-based list of elements which doesn't
+        // have static type information (as opposed to `Functions`) since we
+        // don't know just yet what type the table has. The type will be be
+        // inferred in the next step within `table_init_segment`.
+        let empty = TableSegmentElements::Expressions(Box::new([]));
+
         let elements = match module.passive_elements_map.get(&elem_index) {
             Some(index) if !self.dropped_elements.contains(elem_index) => {
                 &module.passive_elements[*index]

programming_language: Rust
filename: externref-table-dropped-segment-issue-8281.wast
change_type: ModificationType.ADD
diff: @@ -0,0 +1,39 @@
+(module
+  (table $t 0 0 externref)
+
+  (func (export "f1")
+    (i32.const 0)
+    (i32.const 0)
+    (i32.const 0)
+    (table.init $t $declared)
+  )
+
+  (func (export "f2")
+    (i32.const 0)
+    (i32.const 0)
+    (i32.const 0)
+    (table.init $t $passive)
+
+    (elem.drop $passive)
+
+    (i32.const 0)
+    (i32.const 0)
+    (i32.const 0)
+    (table.init $t $passive)
+  )
+
+  (func (export "f3")
+    (i32.const 0)
+    (i32.const 0)
+    (i32.const 0)
+    (table.init $t $active)
+  )
+
+  (elem $declared declare externref)
+  (elem $passive externref)
+  (elem $active (i32.const 0) externref)
+)
+
+(assert_return (invoke "f1"))
+(assert_return (invoke "f2"))
+(assert_return (invoke "f3"))

programming_language: PowerShell