Add rust-ammonia/ammonia#142 (#956)

* Add rust-ammonia/ammonia#142

* Update RUSTSEC-0000-0000.md

* Update RUSTSEC-0000-0000.md

crates/ammonia/RUSTSEC-0000-0000.md

@@ -0,0 +1,39 @@
+```toml
+[advisory]
+id = "RUSTSEC-0000-0000"
+package = "ammonia"
+date = "2021-07-08"
+url = "https://github.com/rust-ammonia/ammonia/pull/142"
+categories = ["format-injection"]
+keywords = ["html", "xss"]
+
+[versions]
+patched = [">= 3.1.0", ">= 2.1.3, < 3.0.0"]
+```
+
+# Incorrect handling of embedded SVG and MathML leads to mutation XSS
+
+Affected versions of this crate did not account for namespace-related parsing
+differences between HTML, SVG, and MathML. Even if the `svg` and `math` elements
+are not allowed, the underlying HTML parser still treats them differently.
+Running cleanup without accounting for these differing namespaces resulted in an "impossible"
+DOM, which appeared "safe" when examining the DOM tree, but when serialized and deserialized,
+could be exploited to inject abitrary markup.
+
+To exploit this, the application using this library must allow a tag that is parsed as raw text in HTML.
+These [elements] are:
+
+* title
+* textarea
+* xmp
+* iframe
+* noembed
+* noframes
+* plaintext
+* noscript
+* style
+* script
+
+Applications that do not explicitly allow any of these tags should not be affected, since none are allowed by default.
+
+[elements]: https://github.com/servo/html5ever/blob/57eb334c0ffccc6f88d563419f0fbeef6ff5741c/html5ever/src/tree_builder/rules.rs