Vulnerability Database

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Total vulnerabilities in the database

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

Inefficient Algorithmic Complexity

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:

  • https://github.com/commonmark/commonmark.js/issues/129
  • https://github.com/commonmark/commonmark.js/issues/157
  • https://github.com/commonmark/commonmark.js/issues/172
  • https://github.com/github/cmark-gfm/security/advisories/GHSA-r572-jvj2-3m8p
  • https://github.com/github/cmark-gfm/security/advisories/GHSA-24f7-9frr-5h2r
  • https://github.com/github/cmark-gfm/security/advisories/GHSA-29g3-96g3-jg6c
  • https://github.com/github/cmark-gfm/security/advisories/GHSA-r8vr-c48j-fcc5
  • https://github.com/github/cmark-gfm/security/advisories/GHSA-w4qg-3vf7-m9x5
  • https://github.com/github/cmark-gfm/security/advisories/GHSA-66g8-4hjf-77xh

For general information about this type of issue:

  • https://en.wikipedia.org/wiki/Time_complexity
  • https://cwe.mitre.org/data/definitions/407.html
  • Published: Dec 9, 2024
  • Updated: Jun 5, 2026
  • GHSA: GHSA-c2pc-g5qf-rfrf
  • Severity: High
  • Exploit:
  • CISA KEV:

CVSS v3:

  • Severity: High
  • Score: 7.5
  • AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CWEs:

Frequently Asked Questions

A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.

Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.

Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.

SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.