CVE-2025-26466:CVE-2025-26466 is a vulnerability in OpenSSH that can lead to a denial of service attack. The flaw is due to the SSH server allocating a pong packet in a memory buffer for each ping packet it receives, which is only freed when the server/client key exchange has finished. A malicious client can exploit this by continuously sending such packets, causing an uncontrolled increase in memory consumption on the server side.

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The vulnerability, identified as CVE-2025-26466, is found in the OpenSSH package. The flaw is due to the SSH server allocating a pong packet in a memory buffer for each ping packet it receives. These packets are stored in a queue and are only freed when the server/client key exchange has finished. A malicious client can exploit this flaw by continuously sending such packets, leading to an uncontrolled increase in memory consumption on the server side. This can cause the server to become unavailable, resulting in a denial of service attack. The vulnerability has a CVSS v3.1 base score of 5.9, indicating a medium severity level.

Overview

CVE-2025-26466 is a vulnerability in OpenSSH that can lead to a denial of service attack. The flaw is due to the SSH server allocating a pong packet in a memory buffer for each ping packet it receives, which is only freed when the server/client key exchange has finished. A malicious client can exploit this by continuously sending such packets, causing an uncontrolled increase in memory consumption on the server side. This can cause the server to become unavailable, resulting in a denial of service attack. The vulnerability has a CVSS v3.1 base score of 5.9, indicating a medium severity level.

Remediation

This issue can be mitigated by setting the following three different options in the sshd configuration file located at: /etc/ssh/sshd_config

MaxStartups: Set to a reasonable value, this option controls the maximum number of concurrent unauthenticated connections the SSH server accepts.

PerSourcePenalties: Set its suboptions to a reasonable value, this option is used to help sshd to detect and drop connections that are potentially malicious for the SSH server.

LoginGraceTime: Set to a reasonable value, this option controls how much time the SSH server will wait the client to authenticate before dropping its connection.

All the three option above needs to be set to implement a full mitigation for this vulnerability.

References

  1. Red Hat Security Advisory
  2. Red Hat Bugzilla
  3. Qualys Security Advisory
  4. NetApp Security Advisory
  5. OpenWall Security Mailing List
  6. SUSE Bugzilla
  7. Debian Security Tracker
  8. Ubuntu Security Notice

Industry ExposureMost to least
This section illustrates the prevalence of a specific Common Vulnerabilities and Exposures (CVE) across various industries based on customer reports. The ranking displays industries from the most to least affected by this particular vulnerability, offering valuable insight into where this CVE has been most frequently observed. This information can help organizations within these sectors prioritize their security efforts, understand their relative risk exposure compared to their peers, and focus remediation strategies where they are most needed. By understanding the industry-specific impact, organizations can make more informed decisions regarding patching, resource allocation, and overall risk management related to this CVE.

  1. Health Care & Social Assistance
    Health Care & Social Assistance
  2. Manufacturing
    Manufacturing
  3. Public Administration
    Public Administration
  4. Educational Services
    Educational Services
  5. Finance and Insurance
    Finance and Insurance
  6. Professional, Scientific, & Technical Services
    Professional, Scientific, & Technical Services
  7. Retail Trade
    Retail Trade
  8. Transportation & Warehousing
    Transportation & Warehousing
  9. Utilities
    Utilities
  10. Arts, Entertainment & Recreation
    Arts, Entertainment & Recreation
  11. Information
    Information
  12. Other Services (except Public Administration)
    Other Services (except Public Administration)
  13. Management of Companies & Enterprises
    Management of Companies & Enterprises
  14. Agriculture, Forestry Fishing & Hunting
    Agriculture, Forestry Fishing & Hunting
  15. Mining
    Mining
  16. Accommodation & Food Services
    Accommodation & Food Services
  17. Construction
    Construction
  18. Real Estate Rental & Leasing
    Real Estate Rental & Leasing
  19. Wholesale Trade
    Wholesale Trade
  20. Administrative, Support, Waste Management & Remediation Services
    Administrative, Support, Waste Management & Remediation Services

Focus on What Matters

  1. See Everything.
  2. Identify True Risk.
  3. Proactively Mitigate Threats.

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Armis Vulnerability Intelligence Database