This fixes the following vulnerability scenario:
* Victim logs into SAFE-HOST on SAFE-IP-ADDRESS regularly.
* Victim is cajoled into connecting to attacker controlled
ATTACK-HOST, on ATTACK-IP-ADDRESS. ATTACK-HOST uses a different host
key type (e.g. Ed25519 vs RSA). The new key is added at the end of
known_hosts.
* Attacker makes DNS system return ATTACK-IP-ADDRESS for SAFE-HOST.
* Victim logs into SAFE-HOST, but is not warned because the host key
matches ATTACK-IP-ADDRESS.
For this attack to work, the key type has to be different, because
knownhosts gives precedence to the first key found for each type. Add
a test that asserts this behavior.
The new semantics simplify the code, but callers that modify
.ssh/known_host interactviely must now take an extra step to remain
OpenSSH compatible: on successful login, the IP address must be
checked without hostname, and if it is not known, added separately to
the known_hosts file, so future logins that use an IP address only
will be protected too.
Thanks to Daniel Parks <security@demonhorse.net> for finding this
vulnerability.
Change-Id: I62b1b60ceb02e2f583a4657213feac1a8885dd42
Reviewed-on: https://go-review.googlesource.com/104939
Reviewed-by: Adam Langley <agl@golang.org>
Run-TryBot: Han-Wen Nienhuys <hanwen@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Consider the following code:
var p *int
a := []int{0, 1, 2, 3}
for _, i := range a {
if i == 1 {
p = &i
}
}
fmt.Println(*p) // Prints 3
This prints 3 because the variable i is the exact same variable across
all iterations of the loop. When the address is taken for some specific
iteration, the user's intent is to capture the value of i at that
given loop, but instead the value of i in the last loop is what remains.
A bug this sort occurs in the check logic since the address of the
knownKey is taken, but is changed upon subsequent iterations of the
loop (which happens when there are multiple lines).
Change-Id: Ic626778cdcde3968dcff4fa5e7206274957dcb04
Reviewed-on: https://go-review.googlesource.com/40937
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Han-Wen Nienhuys
Peter Moody
Joe Tsai