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ssh: don't advertise rsa-sha2 algorithms if we can't use them

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The server implementation looks at the HostKeys to advertise and
negotiate host key signature algorithms. A fundamental issue of the
Signer and AlgorithmSigner interfaces is that they don't expose the
supported signature algorithms, so really the server has to guess.

Currently, it would guess exclusively based on the PublicKey.Type,
regardless of whether the host key implemented AlgorithmSigner. This
means that a legacy Signer that only supports ssh-rsa still led the
server to negotiate rsa-sha2 algorithms. The server would then fail to
find a suitable host key to make the signature and crash.

This won't happen if only Signers from this package are used, but if a
custom Signer that doesn't support SignWithAlgorithm() but returns
"ssh-rsa" from PublicKey().Type() is used as a HostKey, the server is
vulnerable to DoS.

The only workable rules to determine what to advertise seems to be:

   1. a pure Signer will always Sign with the PublicKey.Type

   2. an AlgorithmSigner supports all algorithms associated with the
      PublicKey.Type

Rule number two means that we can't add new supported algorithms in the
future, which is not great, but it's too late to fix that.

rsaSigner was breaking rule number one, and although it would have been
fine where it's used, I didn't want to break our own interface contract.

It's unclear why we had separate test key entries for rsa-sha2
algorithms, since we can use the ssh-rsa key for those. The only test
that used them, TestCertTypes, seemed broken: the init was actually
failing at making the corresponding signers rsaSigners, and indeed the
test for the SHA-256 signer expected and checked a SHA-512 signature.

Pending CVE
For golang/go#49952

Change-Id: Ie658eefcadd87906e63fc7faae8249376aa96c79
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/392355
Trust: Filippo Valsorda <filippo@golang.org>
Run-TryBot: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Roland Shoemaker <roland@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
This commit is contained in:
Filippo Valsorda
2022-03-14 23:46:59 +00:00
parent fcc990c556
commit 1baeb1ce4c
12 changed files with 234 additions and 233 deletions
Download Patch File Download Diff File Expand all files Collapse all files
ssh/testdata/keys.go
Vendored
+1 -33
View File
@@ -60,38 +60,6 @@ NDvRS0rjwt6lJGv7zPZoqDc65VfrK2aNyHx2PgFyzwrEOtuF57bu7pnvEIxpLTeM
z26i6XVMeYXAWZMTloMCQBbpGgEERQpeUknLBqUHhg/wXF6+lFA+vEGnkY+Dwab2
KCXFGd+SQ5GdUcEMe9isUH6DYj/6/yCDoFrXXmpQb+M=
-----END RSA PRIVATE KEY-----
`),
"rsa-sha2-256": []byte(`-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----
`),
"rsa-sha2-512": []byte(`-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----
`),
"pkcs8": []byte(`-----BEGIN PRIVATE KEY-----
MIIEvgIBADANBgkqhkiG9w0BAQEFAASCBKgwggSkAgEAAoIBAQCitzS2KiRQTccf
@@ -226,7 +194,7 @@ var SSHCertificates = map[string][]byte{
`),
"rsa-sha2-256": []byte(`ssh-rsa-cert-v01@openssh.com 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 host.example.com
`),
"rsa-sha2-512": []byte(`ssh-rsa-cert-v01@openssh.com AAAAHHNzaC1yc2EtY2VydC12MDFAb3BlbnNzaC5jb20AAAAgFGv4IpXfs4L/Y0b3rmUdPFhWoUrVnXuPxXr6aHGs7wgAAAADAQABAAAAgQC8A6FGHDiWCSREAXCq6yBfNVr0xCVG2CzvktFNRpue+RXrGs/2a6ySEJQb3IYquw7HlJgu6fg3WIWhOmHCjfpG0PrL4CRwbqQ2LaPPXhJErWYejcD8Di00cF3677+G10KMZk9RXbmHtuBFZT98wxg8j+ZsBMqGM1+7yrWUvynswQAAAAAAAAAAAAAAAgAAABRob3N0LmV4YW1wbGUuY29tLWtleQAAABQAAAAQaG9zdC5leGFtcGxlLmNvbQAAAABeSMRYAAAAAHBPBp4AAAAAAAAAAAAAAAAAAAEXAAAAB3NzaC1yc2EAAAADAQABAAABAQC+D11D0hEbn2Vglv4YRJ8pZNyHjIGmvth3DWOQrq++2vH2MujmGQDxfr4SVE9GpMBlKU3lwGbpgIBxAg6yZcNSfo6PWVU9ACg6NMFO+yMzc2MaG+/naQdNjSewywF5j2rkNO2XOaViRVSrZroe2B/aY2LTV0jDl8nu5NOjwRs1/s7SLe5z1rw/X0dpmXk0qJY3gQhmR8HZZ1dhEkJUGwaBCPd0T8asSYf1Ag2rUD4aQ28r3q69mbwfWOOa6rMemVZruUV5dzHwVNVNtVv+ImtnYtz8m8g+K0plaGptHn3KsaOnASkh3tujhaE7kvc4HR9Igli9+76jhZie3h/dTN5zAAABFAAAAAxyc2Etc2hhMi01MTIAAAEAnF4fVj6mm+UFeNCIf9AKJCv9WzymjjPvzzmaMWWkPWqoV0P0m5SiYfvbY9SbA73Blpv8SOr0DmpublF183kodREia4KyVuC8hLhSCV2Y16hy9MBegOZMepn80w+apj7Rn9QCz5OfEakDdztp6OWTBtqxnZFcTQ4XrgFkNWeWRElGdEvAVNn2WHwHi4EIdz0mdv48Imv5SPlOuW862ZdFG4Do1dUfDIiGsBofLlgcyIYlf+eNHul6sBeUkuwFxisMpI5DQzNp8PX1g/QJA2wzwT674PTqDXNttKjyh50Fdr4sXxm9Gz1+jVLoESvFNa55ERdSyAqNu4wTy11MZsWwSA== host.example.com
"rsa-sha2-512": []byte(`ssh-rsa-cert-v01@openssh.com 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 host.example.com
`),
}