Denial-of-Service in markdown-it via Quadratic Processing in Smartquotes

Executive Summary

This vulnerability exists in markdown-it, a Markdown parser, in versions 14.1.1 and below when the typographer feature is enabled. It is a denial-of-service issue caused by quadratic (O(n^2)) processing in the smartquotes rule. The problem arises because the code repeatedly modifies strings using replaceAt(), which involves O(n) slicing and concatenation for each quote character. This inefficient processing can lead to excessive CPU usage when parsing markdown content that contains many quotes, especially if the markdown is user-supplied.

Although the typographer feature is disabled by default, many production applications enable it for enhanced typography, making this vulnerability relevant in real-world scenarios. The issue has been fixed in version 14.2.0.

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Impact Analysis

This vulnerability can impact you by allowing attackers to cause a denial-of-service (DoS) condition. Specifically, by submitting markdown content with many quote characters, an attacker can trigger excessive CPU consumption due to the inefficient processing in the smartquotes rule. This can degrade or disrupt the availability of services that use markdown-it with the typographer feature enabled.

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Mitigation Strategies

To mitigate this vulnerability, you should upgrade markdown-it to version 14.2.0 or later, where the issue has been fixed.

Additionally, if upgrading is not immediately possible, consider disabling the typographer option (which is disabled by default) to prevent the vulnerable smartquotes rule from being triggered.

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Compliance Impact

This vulnerability causes a denial-of-service condition by allowing excessive CPU consumption when processing quote-heavy, user-supplied markdown with the typographer option enabled. While it impacts service availability, there is no direct information linking this vulnerability to breaches of data confidentiality or integrity.

Since the vulnerability primarily affects availability and does not involve unauthorized data access or disclosure, its impact on compliance with standards like GDPR or HIPAA—which focus heavily on data privacy and protection—is indirect and depends on the context of use.

Organizations relying on markdown-it with typographer enabled should consider the risk of service disruption as part of their availability controls, which may be relevant for compliance frameworks that require maintaining service uptime and availability.

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Detection Guidance

This vulnerability occurs in markdown-it versions 14.1.1 and below when the typographer option is enabled, causing excessive CPU consumption due to quadratic processing in the smartquotes rule.

To detect if your system is affected, first verify the version of markdown-it in use and whether the typographer option is enabled.

• Check the installed markdown-it version, for example by running: npm list markdown-it
• Inspect your application configuration or code to see if the typographer option is set to true when initializing markdown-it.

Monitoring CPU usage during markdown parsing of quote-heavy user input may also help identify if the vulnerability is being triggered.

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