Public Access
jaap-jan
4c7f47c026
Pins are stored per algorithm, so an endpoint pinned for ssh-ed25519 that was answered with only an ECDSA or RSA key found no pin and raised SshHostKeyUnknownException: the first-use question, where a pin exists to produce a hard refusal. Anybody in the middle needed nothing more than a key of a different type. The connection factory now reads every pin for the endpoint before the handshake, offers the pinned algorithms first so a server that still holds its pinned key negotiates it, and in the gate accepts a key under an unpinned algorithm only when its fingerprint matches one of the endpoint's pins (one RSA key signs as rsa-sha2-256 and rsa-sha2-512). Anything else is a mismatch. IKnownHostStore gains FindForEndpointAsync for this.
70 lines
2.9 KiB
C#
70 lines
2.9 KiB
C#
namespace DodoSSH.Client.Ssh.Tests;
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/// <summary>
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/// A pin is a pin for the endpoint, whichever key type the server answers with.
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/// </summary>
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/// <remarks>
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/// Pins are stored per algorithm, and the gap these close was that an endpoint whose only pins were for
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/// other algorithms read as a host never seen before. Somebody in the middle needed nothing more than a key
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/// of a different type to turn the hard refusal a pin exists for into a first-use question the user is
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/// invited to click through.
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/// </remarks>
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[Collection(SshCollection.Name)]
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public sealed class HostKeyPinningTests(SshServerFixture fixture)
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{
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private static CancellationToken Token => TestContext.Current.CancellationToken;
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/// <summary>
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/// The endpoint is pinned under a key type this server does not have, which is exactly what a server in
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/// the middle looks like from here: the pinned key is not on offer, and a key of another type is.
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/// </summary>
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[Fact]
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public async Task AKeyOfAnotherTypeOnAPinnedEndpoint_IsAMismatchRatherThanAnUnknownHost()
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{
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var knownHosts = new InMemoryKnownHostStore();
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await knownHosts.TrustAsync(
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new HostKeyPresentation(fixture.Host, fixture.Port, "ssh-dss", "SHA256:the-key-that-was-approved"),
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Token);
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var mismatch = await Should.ThrowAsync<SshHostKeyMismatchException>(async () =>
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await new SshNetConnectionFactory(knownHosts).ConnectAsync(Request(), progress: null, Token));
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mismatch.PinnedFingerprint.ShouldBe("SHA256:the-key-that-was-approved");
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}
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/// <summary>
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/// The same public key under another algorithm's name — an RSA key signs as <c>rsa-sha2-256</c> or
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/// <c>rsa-sha2-512</c> — is the key that was approved, and its fingerprint is what says so.
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/// </summary>
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[Fact]
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public async Task TheApprovedKeyUnderAnotherAlgorithmName_IsStillTrusted()
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{
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var learned = new InMemoryKnownHostStore();
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var unknown = await Should.ThrowAsync<SshHostKeyUnknownException>(async () =>
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await new SshNetConnectionFactory(learned).ConnectAsync(Request(), progress: null, Token));
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var knownHosts = new InMemoryKnownHostStore();
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await knownHosts.TrustAsync(unknown.Presentation with { Algorithm = "x-renamed-algorithm" }, Token);
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await using var connection = await new SshNetConnectionFactory(knownHosts)
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.ConnectAsync(Request(), progress: null, Token);
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connection.ShouldNotBeNull();
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}
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[Fact]
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public async Task AnEndpointWithNoPinsAtAll_IsStillAnUnknownHost() =>
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await Should.ThrowAsync<SshHostKeyUnknownException>(async () =>
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await new SshNetConnectionFactory(new InMemoryKnownHostStore())
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.ConnectAsync(Request(), progress: null, Token));
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private SshConnectionRequest Request() => new(
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fixture.Host,
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fixture.Port,
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SshServerFixture.Username,
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new SshPasswordCredential(SshServerFixture.Password));
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}
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