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PatchSiren cyber security CVE debrief

CVE-2026-59887 markdown-it CVE debrief

CVE-2026-59887 is a denial of service vulnerability in the linkify-it library. The vulnerability is caused by the mailto: schema validator used by .test() and .match() which can be invoked at every mailto: occurrence and scan the remaining input, leading to O(n^2) CPU consumption on crafted user text. This issue is fixed in version 5.0.2. The vulnerability has a high CVSS score of 7.5 and can be exploited by crafted user text, potentially causing performance issues and leading to a denial of service.

Vendor
markdown-it
Product
linkify-it
CVSS
HIGH 7.5
CISA KEV
Not listed in stored evidence
Original CVE published
2026-07-08
Original CVE updated
2026-08-26
Advisory published
2026-07-08
Advisory updated
2026-08-26

Who should care

Developers and users of the linkify-it library should be aware of this vulnerability and take steps to mitigate it. This vulnerability has a high CVSS score of 7.5 and can be exploited by crafted user text, potentially causing performance issues and leading to a denial of service. Affected operators, platforms, and security teams should review and address this vulnerability.

Technical summary

The linkify-it library prior to version 5.0.2 contains a denial of service vulnerability. The vulnerability is caused by the mailto: schema validator used by .test() and .match() which can be invoked at every mailto: occurrence and scan the remaining input, leading to O(n^2) CPU consumption on crafted user text. This can cause performance issues and potentially lead to a denial of service. The vulnerability has a high CVSS score of 7.5.

Defensive priority

High

Recommended defensive actions

  • Update to version 5.0.2 or later
  • Validate and sanitize user input
  • Monitor for suspicious activity
  • Review compensating controls for exposed systems while remediation is scheduled and verified
  • Check relevant monitoring, detection, and logs for exposed assets that need extra review
  • Track exceptions, retest remediated assets, and close the item only after evidence is documented
  • Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The CVE record was published on 2026-07-08T17:17:26.883Z and was last modified on 2026-07-10T19:13:03.283Z. The NVD entry is currently Awaiting Analysis. This information is based on the provided source corpus. Further verification is recommended to confirm the accuracy of this information.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-59887 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-59887

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-59887 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-59887

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.