Attacker Value
Unknown
(0 users assessed)
Exploitability
Unknown
(0 users assessed)
User Interaction
None
Privileges Required
Low
Attack Vector
Network
0

CVE-2021-3634

Disclosure Date: August 31, 2021
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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.

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CVSS V3 Severity and Metrics
Base Score:
6.5 Medium
Impact Score:
3.6
Exploitability Score:
2.8
Vector:
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Attack Vector (AV):
Network
Attack Complexity (AC):
Low
Privileges Required (PR):
Low
User Interaction (UI):
None
Scope (S):
Unchanged
Confidentiality (C):
None
Integrity (I):
None
Availability (A):
High

General Information

Vendors

  • debian,
  • fedoraproject,
  • libssh,
  • netapp,
  • oracle,
  • redhat

Products

  • cloud backup -,
  • debian linux 10.0,
  • debian linux 11.0,
  • enterprise linux 8.0,
  • fedora 33,
  • fedora 34,
  • fedora 35,
  • libssh,
  • mysql workbench,
  • virtualization 4.0
Technical Analysis