What is the reason for the maximum alias number in the npm YAML library?

Question

What is the reason for the maximum alias number in the npm YAML library?

I have been utilizing the npm module yaml to convert complex, interdependent JavaScript objects into a text format that can be easily restored in Javascript. Additionally, I use this package for deep copying of deeply nested objects by serializing and then deserializing them.

Recently, I encountered an error message related to the maximum object size:

Excessive alias count indicates a resource exhaustion attack

Is there a real risk when serializing inter-referential objects if YAML only creates alias references? (There shouldn't be any issues with cyclic traversal in the graph, correct?) – Is there a way to bypass or adjust this max limit, or perhaps an alternative method for storing inter-referential objects as text / deep-copying them?

Thank you!

Edit: I decided to go with flyx's response as it provided a clearer explanation on why there is a limitation on alias count, while rexfordkelly offered insights on how to deactivate this check within the npm yaml library.

javascript npm yaml

Answer 1

Answer №1

Certain YAML frameworks may be susceptible to the phenomenon known as the billion laughs attack. An illustration of this is showcased below:

a: &a ["lol","lol","lol","lol","lol","lol","lol","lol","lol"]
b: &b [*a,*a,*a,*a,*a,*a,*a,*a,*a]
c: &c [*b,*b,*b,*b,*b,*b,*b,*b,*b]
d: &d [*c,*c,*c,*c,*c,*c,*c,*c,*c]
e: &e [*d,*d,*d,*d,*d,*d,*d,*d,*d]
f: &f [*e,*e,*e,*e,*e,*e,*e,*e,*e]
g: &g [*f,*f,*f,*f,*f,*f,*f,*f,*f]
h: &h [*g,*g,*g,*g,*g,*g,*g,*g,*g]
i: &i [*h,*h,*h,*h,*h,*h,*h,*h,*h]

You can experiment with this scenario using the online demonstration of js-yaml, which may struggle to process it due to its limitations. While anchors and aliases are intended for generating references rather than copies according to YAML specifications, some implementations mistakenly duplicate the lists instead (even PyYAML has been known to exhibit this behavior). Many other YAML frameworks are essentially variations or derivatives of PyYAML in various programming languages.

Answer 2

Certain YAML frameworks may be susceptible to the phenomenon known as the billion laughs attack. An illustration of this is showcased below:

a: &a ["lol","lol","lol","lol","lol","lol","lol","lol","lol"]
b: &b [*a,*a,*a,*a,*a,*a,*a,*a,*a]
c: &c [*b,*b,*b,*b,*b,*b,*b,*b,*b]
d: &d [*c,*c,*c,*c,*c,*c,*c,*c,*c]
e: &e [*d,*d,*d,*d,*d,*d,*d,*d,*d]
f: &f [*e,*e,*e,*e,*e,*e,*e,*e,*e]
g: &g [*f,*f,*f,*f,*f,*f,*f,*f,*f]
h: &h [*g,*g,*g,*g,*g,*g,*g,*g,*g]
i: &i [*h,*h,*h,*h,*h,*h,*h,*h,*h]

You can experiment with this scenario using the online demonstration of js-yaml, which may struggle to process it due to its limitations. While anchors and aliases are intended for generating references rather than copies according to YAML specifications, some implementations mistakenly duplicate the lists instead (even PyYAML has been known to exhibit this behavior). Many other YAML frameworks are essentially variations or derivatives of PyYAML in various programming languages.

Answer 3

Answer №2

To bypass this verification, simply set maxAliasCount=-1 in the yaml parse options.

The purpose of YAML is to prevent potential denial of service attacks. If your YAML file does not contain any user-input data and is secure, you can consider turning off these security checks.

However, there is a risk of resource depletion when processing large YAML files.

I recommend testing and analyzing its performance before making any changes.

Answer 4

To bypass this verification, simply set maxAliasCount=-1 in the yaml parse options.

The purpose of YAML is to prevent potential denial of service attacks. If your YAML file does not contain any user-input data and is secure, you can consider turning off these security checks.

However, there is a risk of resource depletion when processing large YAML files.

I recommend testing and analyzing its performance before making any changes.

What is the reason for the maximum alias number in the npm YAML library?

Answer №1

Answer №2

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