https://bugzilla.mindrot.org/show_bug.cgi?id=2547
Bug ID: 2547
Summary: ssh-ext-info: missing server signature algorithms
Product: Portable OpenSSH
Version: 7.2p1
Hardware: All
OS: All
Status: NEW
Severity: normal
Priority: P5
Component: sshd
Assignee: [email protected]
Reporter: [email protected]
In the "server-sig-algs" extension the server sends to the client, sshd
only includes the rsa signature algorithms [1]:
(r = sshpkt_put_cstring(ssh, "rsa-sha2-256,rsa-sha2-512")) != 0 ||
However, it should include all signature algorithms (including
ecdsa-sha2-*, ssh-ed25519, etc) it supports.
This is what the RFC [2] says:
string "server-sig-algs"
This extension is sent by the server only, and contains a list of
signature algorithms that the server is able to process as part of a
"publickey" request.
You may have incorrectly assumed that there is only 1 signature
algorithm for the omitted public key algorithms. For example for ECDSA
private keys there are at least two known signature algorithms:
ecdsa-sha2-nistp256
x509v3-ecdsa-sha2-nistp256 (from rfc6187)
References:
[1] https://github.com/openssh/openssh-portable/blob/master/kex.c#L344
[2] https://tools.ietf.org/html/draft-ssh-ext-info-05#section-3.1
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