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Ubuntu 26.04 libssh2 Critical Denial of Service USN-8309

Linuxsecurity •LinuxSecurity Advisories • May 26, 2026

A security issue affects these releases of Ubuntu and its derivatives: - Ubuntu 26.04 LTS - Ubuntu 25.10 - Ubuntu 24.04 LTS Summary: libssh2 could be made to crash if it received specially crafted network traffic. Software Description: - libssh2: Client-side C library implementing the SSH2 protocol Details: It was discovered that libssh2 incorrectly handled username and password length values during SSH password authentication. A remote attacker could possibly use this issue to cause a denial of service.

The problem can be corrected by updating your system to the following package versions: Ubuntu 26.04 LTS libssh2-1t64 1.11.1-1ubuntu0.26.04.1 Ubuntu 25.10 libssh2-1t64 1.11.1-1ubuntu0.25.10.1 Ubuntu 24.04 LTS libssh2-1t64 1.11.0-4.1ubuntu0.24.04.1 In general, a standard system update will make all the necessary changes.

Ubuntu Security Notice USN-8309-1

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This article is one source in a clustered incident — the cluster page carries the summary, timeline and every other outlet covering it.

Critical libssh2 Vulnerability Causes Denial of Service Risk in Ubuntu A vulnerability in libssh2 has been identified, affecting multiple Ubuntu releases including 26.04 LTS, 25.10, and 24.04 LTS. The flaw arises from improper handling of username and password length values during SSH password authentication, which could allow remote attackers to exploit the issue and potentially cause a denial of service. Users are advised to update their systems to the latest package versions to mitigate the risk. The vulnerability is categorized under USN-8309-1, and a standard system update will apply the necessary patches. Ubuntu Pro offers ten-year security coverage for affected packages, ensuring continued support for users. The issue emphasizes the importance of regular updates to maintain system security. 2 sources 58

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Ubuntu 26.04 libssh2 Critical Denial of Service USN-8309

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