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CVE-2021-3634

6.5 · MEDIUM

A flaw has been found in libssh in versions prior to 0.9.6.

Published Aug 31, 2021CWE-787EPSS 4.68%

Overview

CVE-2021-3634 is a medium-severity vulnerability. It was published on August 31, 2021 and has a CVSS 3.1 base score of 6.5 (MEDIUM).

This vulnerability has a CVSS 3.1 base score of 6.5, rated MEDIUM. It can be exploited remotely over the network. Some level of privileges is required for exploitation.

Technical description

A flaw has been found in libssh in versions prior to 0.9.6. The SSH protocol keeps track of two shared secrets during the lifetime of the session. One of them is called secret_hash and the other session_id. Initially, both of them are the same, but after key re-exchange, previous session_id is kept and used as an input to new secret_hash. Historically, both of these buffers had shared length variable, which worked as long as these buffers were same. But the key re-exchange operation can also change the key exchange method, which can be based on hash of different size, eventually creating "secret_hash" of different size than the session_id has. This becomes an issue when the session_id memory is zeroed or when it is used again during second key re-exchange.

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References

Refbugzilla.redhat.com/show_bug.cgi?id=1978810Reflists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/DRK67AJCWYYVAGF5SGAHNZXCX3PN3ZFP/Reflists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/JKYD3ZRAMDAQX3ZW6THHUF3GXN7FF6B4/Reflists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/SVWAAB2XMKEUMPMDALINKAA4U2QM4LNG/Refsecurity.gentoo.org/glsa/202312-05Refsecurity.netapp.com/advisory/ntap-20211004-0003/Refwww.debian.org/security/2021/dsa-4965Refwww.oracle.com/security-alerts/cpujan2022.htmlRefbugzilla.redhat.com/show_bug.cgi?id=1978810Reflists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/DRK67AJCWYYVAGF5SGAHNZXCX3PN3ZFP/

How CyberStrike helps

Frequently asked questions

What is CVE-2021-3634?

CVE-2021-3634 is a medium-severity vulnerability. It was published on August 31, 2021 and has a CVSS 3.1 base score of 6.5 (MEDIUM).

How severe is CVE-2021-3634?

This vulnerability has a CVSS 3.1 base score of 6.5, rated MEDIUM. It can be exploited remotely over the network. Some level of privileges is required for exploitation.

How do I fix or remediate CVE-2021-3634?

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2021-3634?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2021-3634 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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