CVE-2021-3634 Detail

Current 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.


View Analysis Description

Severity



CVSS 3.x Severity and Metrics:

NIST CVSS score
NIST: NVD
Base Score:  6.5 MEDIUM
Vector:  CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H


NVD Analysts use publicly available information to associate vector strings and CVSS scores. We also display any CVSS information provided within the CVE List from the CNA.

Note: NVD Analysts have published a CVSS score for this CVE based on publicly available information at the time of analysis. The CNA has not provided a score within the CVE List.

References to Advisories, Solutions, and Tools

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Hyperlink Resource
https://bugzilla.redhat.com/show_bug.cgi?id=1978810 Issue Tracking  Third Party Advisory 
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/DRK67AJCWYYVAGF5SGAHNZXCX3PN3ZFP/ Mailing List  Third Party Advisory 
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/JKYD3ZRAMDAQX3ZW6THHUF3GXN7FF6B4/ Mailing List  Third Party Advisory 
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/SVWAAB2XMKEUMPMDALINKAA4U2QM4LNG/ Mailing List  Third Party Advisory 
https://security.netapp.com/advisory/ntap-20211004-0003/ Third Party Advisory 
https://www.debian.org/security/2021/dsa-4965 Third Party Advisory 

Weakness Enumeration

CWE-ID CWE Name Source
CWE-787 Out-of-bounds Write cwe source acceptance level NIST  
CWE-119 Improper Restriction of Operations within the Bounds of a Memory Buffer Provider acceptance level Red Hat, Inc.  

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Change History

7 change records found show changes

Quick Info

CVE Dictionary Entry:
CVE-2021-3634
NVD Published Date:
08/31/2021
NVD Last Modified:
10/18/2021
Source:
Red Hat, Inc.