OpenSSH 7.6p1 ssh-agent exiting if passed an invalid key blob

Ron Frederick ronf at
Wed Nov 15 13:48:10 AEDT 2017

On Nov 14, 2017, at 5:43 PM, Damien Miller <djm at> wrote:
> On Tue, 14 Nov 2017, Ron Frederick wrote:
>> Thanks Damien, but I’m not sure this is a good fix. Now both cases
>> turn into an error(), but if there is a problem reading the initial
>> pair of strings and u32 value, you really can’t safely keep the
>> connection open to receive additional requests.
> That's not the case: this function is called in the context of one
> message with delimited length (see process_message()). A failure here
> just disregards that message and doesn't need to kill the entire
> connection.
> There are some other input parsing cases that should be downgraded
> from fatal() in ssh-agent.c, but I'll do those separately.

Ah, ok - my mistake. I didn’t remember there was an overall length field on each message, but going back and looking at my client code, I see you’re right. In that case, I agree that it shouldn’t be a problem to allow parsing failures at this level, or in similar places for other messages.

Thanks very much!
Ron Frederick
ronf at

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