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

2025-06-21 18:23:40 +02:00 · 2023-09-03 16:13:00 -04:00
parent 3f2fdbaa3d
commit 199e75f6cd
19 changed files with 100 additions and 104 deletions
--- a/test/docker/expected_results/openssh_8.0p1_builtin_policy_test1.json
+++ b/test/docker/expected_results/openssh_8.0p1_builtin_policy_test1.json
@ -27,5 +27,5 @@
    ],
    "host": "localhost",
    "passed": false,
-    "policy": "Hardened OpenSSH Server v8.0 (version 2)"
+    "policy": "Hardened OpenSSH Server v8.0 (version 3)"
 }
--- a/test/docker/expected_results/openssh_8.0p1_builtin_policy_test1.txt
+++ b/test/docker/expected_results/openssh_8.0p1_builtin_policy_test1.txt
@ -1,5 +1,5 @@
 Host:   localhost:2222
-Policy: Hardened OpenSSH Server v8.0 (version 2)
+Policy: Hardened OpenSSH Server v8.0 (version 3)
 Result: [0;31m❌ Failed![0m
 [0;33m
 Errors:
--- a/test/docker/expected_results/openssh_8.0p1_builtin_policy_test2.json
+++ b/test/docker/expected_results/openssh_8.0p1_builtin_policy_test2.json
@ -50,5 +50,5 @@
    ],
    "host": "localhost",
    "passed": false,
-    "policy": "Hardened OpenSSH Server v8.0 (version 2)"
+    "policy": "Hardened OpenSSH Server v8.0 (version 3)"
 }
--- a/test/docker/expected_results/openssh_8.0p1_builtin_policy_test2.txt
+++ b/test/docker/expected_results/openssh_8.0p1_builtin_policy_test2.txt
@ -1,5 +1,5 @@
 Host:   localhost:2222
-Policy: Hardened OpenSSH Server v8.0 (version 2)
+Policy: Hardened OpenSSH Server v8.0 (version 3)
 Result: [0;31m❌ Failed![0m
 [0;33m
 Errors:
--- a/test/docker/expected_results/openssh_8.0p1_custom_policy_test14.json
+++ b/test/docker/expected_results/openssh_8.0p1_custom_policy_test14.json
@ -2,13 +2,13 @@
    "errors": [
        {
            "actual": [
-                "2048"
+                "4096"
            ],
            "expected_optional": [
                ""
            ],
            "expected_required": [
-                "4096"
+                "8192"
            ],
            "mismatched_field": "Group exchange (diffie-hellman-group-exchange-sha256) modulus sizes"
        }
--- a/test/docker/expected_results/openssh_8.0p1_custom_policy_test14.txt
+++ b/test/docker/expected_results/openssh_8.0p1_custom_policy_test14.txt
@ -16,6 +16,6 @@ Result: [0;31m❌ Failed![0m
 [0;33m
 Errors:
  * Group exchange (diffie-hellman-group-exchange-sha256) modulus sizes did not match.
-    - Expected: 4096
-    - Actual:   2048
+    - Expected: 8192
+    - Actual:   4096
 [0m
--- a/test/docker/expected_results/openssh_8.0p1_test1.json
+++ b/test/docker/expected_results/openssh_8.0p1_test1.json
@ -82,7 +82,7 @@
        },
        {
            "algorithm": "diffie-hellman-group-exchange-sha256",
-            "keysize": 2048
+            "keysize": 4096
        },
        {
            "algorithm": "diffie-hellman-group16-sha512"
--- a/test/docker/expected_results/openssh_8.0p1_test1.txt
+++ b/test/docker/expected_results/openssh_8.0p1_test1.txt
@ -21,9 +21,8 @@
                                            `- [info] available since OpenSSH 5.7, Dropbear SSH 2013.62
 [0;31m(kex) ecdh-sha2-nistp521                    -- [fail] using elliptic curves that are suspected as being backdoored by the U.S. National Security Agency[0m
                                            `- [info] available since OpenSSH 5.7, Dropbear SSH 2013.62
-[0;33m(kex) diffie-hellman-group-exchange-sha256 (2048-bit) -- [warn] 2048-bit modulus only provides 112-bits of symmetric strength[0m
-                                                      `- [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)
+[0;32m(kex) diffie-hellman-group-exchange-sha256 (4096-bit) -- [info] available since OpenSSH 4.4[0m
+                                                      `- [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).
 [0;32m(kex) diffie-hellman-group16-sha512         -- [info] available since OpenSSH 7.3, Dropbear SSH 2016.73[0m
 [0;32m(kex) diffie-hellman-group18-sha512         -- [info] available since OpenSSH 7.3[0m
 [0;33m(kex) diffie-hellman-group14-sha256         -- [warn] 2048-bit modulus only provides 112-bits of symmetric strength[0m
--- a/test/docker/expected_results/openssh_8.0p1_test2.json
+++ b/test/docker/expected_results/openssh_8.0p1_test2.json
@ -72,7 +72,7 @@
        },
        {
            "algorithm": "diffie-hellman-group-exchange-sha256",
-            "keysize": 2048
+            "keysize": 4096
        },
        {
            "algorithm": "diffie-hellman-group16-sha512"
--- a/test/docker/expected_results/openssh_8.0p1_test2.txt
+++ b/test/docker/expected_results/openssh_8.0p1_test2.txt
@ -21,9 +21,8 @@
                                            `- [info] available since OpenSSH 5.7, Dropbear SSH 2013.62
 [0;31m(kex) ecdh-sha2-nistp521                    -- [fail] using elliptic curves that are suspected as being backdoored by the U.S. National Security Agency[0m
                                            `- [info] available since OpenSSH 5.7, Dropbear SSH 2013.62
-[0;33m(kex) diffie-hellman-group-exchange-sha256 (2048-bit) -- [warn] 2048-bit modulus only provides 112-bits of symmetric strength[0m
-                                                      `- [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)
+[0;32m(kex) diffie-hellman-group-exchange-sha256 (4096-bit) -- [info] available since OpenSSH 4.4[0m
+                                                      `- [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).
 [0;32m(kex) diffie-hellman-group16-sha512         -- [info] available since OpenSSH 7.3, Dropbear SSH 2016.73[0m
 [0;32m(kex) diffie-hellman-group18-sha512         -- [info] available since OpenSSH 7.3[0m
 [0;33m(kex) diffie-hellman-group14-sha256         -- [warn] 2048-bit modulus only provides 112-bits of symmetric strength[0m
--- a/test/docker/expected_results/openssh_8.0p1_test3.json
+++ b/test/docker/expected_results/openssh_8.0p1_test3.json
@ -63,7 +63,7 @@
        },
        {
            "algorithm": "diffie-hellman-group-exchange-sha256",
-            "keysize": 2048
+            "keysize": 4096
        }
    ],
    "key": [
--- a/test/docker/expected_results/openssh_8.0p1_test3.txt
+++ b/test/docker/expected_results/openssh_8.0p1_test3.txt
@ -15,9 +15,8 @@
                                            `- [info] default key exchange since OpenSSH 6.4
 [0;32m(kex) curve25519-sha256@libssh.org          -- [info] available since OpenSSH 6.4, Dropbear SSH 2013.62[0m
                                            `- [info] default key exchange since OpenSSH 6.4
-[0;33m(kex) diffie-hellman-group-exchange-sha256 (2048-bit) -- [warn] 2048-bit modulus only provides 112-bits of symmetric strength[0m
-                                                      `- [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)
+[0;32m(kex) diffie-hellman-group-exchange-sha256 (4096-bit) -- [info] available since OpenSSH 4.4[0m
+                                                      `- [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).

 [0;36m# host-key algorithms[0m
 [0;32m(key) ssh-ed25519                           -- [info] available since OpenSSH 6.5[0m
--- a/test/docker/policies/policy_test13.txt
+++ b/test/docker/policies/policy_test13.txt
@ -23,7 +23,7 @@ hostkey_size_rsa-sha2-512 = 3072
 hostkey_size_ssh-rsa = 3072

 # Group exchange DH modulus sizes.
-dh_modulus_size_diffie-hellman-group-exchange-sha256 = 2048
+dh_modulus_size_diffie-hellman-group-exchange-sha256 = 4096

 # The host key types that must match exactly (order matters).
 host keys = rsa-sha2-512, rsa-sha2-256, ssh-rsa, ecdsa-sha2-nistp256, ssh-ed25519
--- a/test/docker/policies/policy_test14.txt
+++ b/test/docker/policies/policy_test14.txt
@ -23,7 +23,7 @@ hostkey_size_rsa-sha2-512 = 3072
 hostkey_size_ssh-rsa = 3072

 # Group exchange DH modulus sizes.
-dh_modulus_size_diffie-hellman-group-exchange-sha256 = 4096
+dh_modulus_size_diffie-hellman-group-exchange-sha256 = 8192

 # The host key types that must match exactly (order matters).
 host keys = rsa-sha2-512, rsa-sha2-256, ssh-rsa, ecdsa-sha2-nistp256, ssh-ed25519