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league/commonmark's quadratic complexity bugs may lead to a denial of service

High severity GitHub Reviewed Published Dec 7, 2024 in thephpleague/commonmark • Updated Dec 9, 2024

Package

composer league/commonmark (Composer)

Affected versions

< 2.6.0

Patched versions

2.6.0

Description

Impact

Several polynomial time complexity issues in league/commonmark may lead to unbounded resource exhaustion and subsequent denial of service.

Malicious users could trigger that inefficient code with carefully crafted Markdown inputs that are specifically designed to ensure the worst-case performance is reached. Sending multiple such requests in parallel could tie up all available CPU resources and/or PHP-FPM processes, leading to denial of service for legitimate users.

Patches

These vulnerabilities have been patched in version 2.6.0. All users on older versions are highly encouraged to upgrade as soon as possible.

Workarounds

If you cannot upgrade, you may be able to mitigate the issues by:

  • Setting very low memory_limit and max_execution_time PHP configurations to prevent runaway resource usage
  • Implementing rate-limiting, bot protection, or other approaches to reduce the risk of simultaneous bad requests hitting your site
  • Limiting the size of inputs fed into this library (specifically the max length of each line)
  • Limiting the use of this library to trusted users

References

Most of these issues were discovered in other Markdown parsers. You can read more about them here:

For general information about this type of issue:

References

@colinodell colinodell published to thephpleague/commonmark Dec 7, 2024
Published to the GitHub Advisory Database Dec 9, 2024
Reviewed Dec 9, 2024
Last updated Dec 9, 2024

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS score

Weaknesses

Inefficient Algorithmic Complexity

An algorithm in a product has an inefficient worst-case computational complexity that may be detrimental to system performance and can be triggered by an attacker, typically using crafted manipulations that ensure that the worst case is being reached. Learn more on MITRE.

CVE ID

No known CVE

GHSA ID

GHSA-c2pc-g5qf-rfrf

Source code

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