Bug 1978810 (CVE-2021-3634)

Summary: CVE-2021-3634 libssh: possible heap-based buffer overflow when rekeying
Product: [Other] Security Response Reporter: Guilherme de Almeida Suckevicz <gsuckevi>
Component: vulnerabilityAssignee: Red Hat Product Security <security-response-team>
Status: CLOSED ERRATA QA Contact:
Severity: low Docs Contact:
Priority: low    
Version: unspecifiedCC: ansasaki, asn, bishop, caswilli, dblechte, devthomp, dfediuck, djuran, eedri, elima, erik-fedora, fidencio, fjansen, jjelen, jnakfour, kaycoth, kdudka, marcandre.lureau, mgoldboi, michal.skrivanek, mike, mperina, mpitt, negativo17, paul, psegedy, rdieter, redhat-bugzilla, rjones, sahana, sbonazzo, security-response-team, sherold, vmugicag, yturgema
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
Whiteboard:
Fixed In Version: libssh 0.9.6 Doc Type: If docs needed, set a value
Doc Text:
A flaw has been found in libssh. 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.
 Story Points: ---
Clone Of: Environment:
Last Closed: 2021-08-26 13:34:15 UTC Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Bug Depends On: 1994600, 1994605, 1994607, 1998135, 1998136, 1998137, 1998139, 1998140    
Bug Blocks: 1976967, 1978811    

Description Guilherme de Almeida Suckevicz 2021-07-02 19:54:56 UTC 
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 zeroized or when it is used again during second key re-exchange.
Comment 4 devthomp 2021-08-26 13:22:07 UTC 
Created libssh tracking bugs for this issue:

Affects: epel-7 [bug 1998139]
Affects: fedora-all [bug 1998135]


Created libssh2 tracking bugs for this issue:

Affects: epel-8 [bug 1998140]
Affects: fedora-all [bug 1998136]


Created mingw-libssh2 tracking bugs for this issue:

Affects: fedora-all [bug 1998137]
Comment 6 devthomp 2021-08-26 13:34:15 UTC 
Embargo lifted, patch attached, analysis has been completed resolving..
Comment 9 errata-xmlrpc 2022-05-10 15:03:13 UTC 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 8

Via RHSA-2022:2031 https://access.redhat.com/errata/RHSA-2022:2031