Refined GEX testing against OpenSSH servers: when the fallback mechanism is suspected of being triggered, perform an additional test to obtain more accurate results.

This commit is contained in:
Joe Testa
2023-09-03 16:13:00 -04:00
parent 3f2fdbaa3d
commit 199e75f6cd
19 changed files with 100 additions and 104 deletions

View File

@ -15,9 +15,8 @@
`- [info] default key exchange since OpenSSH 6.4
(kex) curve25519-sha256@libssh.org -- [info] available since OpenSSH 6.4, Dropbear SSH 2013.62
`- [info] default key exchange since OpenSSH 6.4
(kex) diffie-hellman-group-exchange-sha256 (2048-bit) -- [warn] 2048-bit modulus only provides 112-bits of symmetric strength
`- [info] available since OpenSSH 4.4
`- [info] A bug in OpenSSH causes it to fall back to a 2048-bit modulus regardless of server configuration (https://bugzilla.mindrot.org/show_bug.cgi?id=2793)
(kex) diffie-hellman-group-exchange-sha256 (4096-bit) -- [info] available since OpenSSH 4.4
`- [info] OpenSSH's GEX fallback mechanism was triggered during testing. Very old SSH clients will still be able to create connections using a 2048-bit modulus, though modern clients will use 4096. This can only be disabled by recompiling the code (see https://github.com/openssh/openssh-portable/blob/V_9_4/dh.c#L477).
# host-key algorithms
(key) ssh-ed25519 -- [info] available since OpenSSH 6.5