Описание
SVGO DoS through entity expansion in DOCTYPE (Billion Laughs)
Summary
SVGO accepts XML with custom entities, without guards against entity expansion or recursion. This can result in a small XML file (811 bytes) stalling the application and even crashing the Node.js process with JavaScript heap out of memory.
Details
The upstream XML parser (sax) doesn't interpret custom XML entities by default. We pattern matched custom XML entities from the DOCTYPE, inserting them into parser.ENTITIES, and enabled unparsedEntities. This gives us the desired behavior of supporting SVGs with entities declared in the DOCTYPE.
However, entities can reference other entities, which can enable small SVGs to explode exponentially when we try to parse them.
Proof of Concept
Impact
If SVGO is run on untrusted input (i.e., user uploaded to server-side application), then the untrusted SVG can effectively stall or crash the application with an SVG < 1 KB in size.
It's unlikely to impact users who just use SVGO locally on their own SVGs or in build pipelines.
Patches
SVGO has patched v4.0.1, v3.3.3, and v2.8.1! However, it's strongly recommended to upgrade to v4 regardless, as previous versions are not officially supported anymore.
Workarounds
== 4.0.0
For v4, users do not specifically have to upgrade SVGO, though it is recommended to do so. A package manager can be used to upgrade sax recursively:
For example:
New options were introduced upstream which makes the way SVGO parses SVGs safe by default.
>= 2.1.0, <= 3.3.2
Users of v3 and v2 will have to take manual action. If users can't upgrade, they may be able to work around this as long as the project doesn't require support for custom XML entities, though it's not a simple flag.
Parse the DOCTYPE directly and check for the presence of custom entities. If entities are present, throw/escape before passing them to SVGO.
Resources
Пакеты
svgo
>= 2.1.0, < 2.8.1
2.8.1
svgo
>= 3.0.0, < 3.3.3
3.3.3
svgo
= 4.0.0
4.0.1
Связанные уязвимости
A flaw was found in SVGO, an SVG (Scalable Vector Graphics) Optimizer. This vulnerability allows a remote attacker to cause a Denial of Service (DoS) by submitting a specially crafted XML file. The application's failure to properly guard against XML entity expansion or recursion can lead to the Node.js process consuming excessive memory and crashing.
SVGO, short for SVG Optimizer, is a Node.js library and command-line application for optimizing SVG files. From version 2.1.0 to before version 2.8.1, from version 3.0.0 to before version 3.3.3, and before version 4.0.1, SVGO accepts XML with custom entities, without guards against entity expansion or recursion. This can result in a small XML file (811 bytes) stalling the application and even crashing the Node.js process with JavaScript heap out of memory. This issue has been patched in versions 2.8.1, 3.3.3, and 4.0.1.
SVGO, short for SVG Optimizer, is a Node.js library and command-line a ...