Fix timing information leak allowing discovery of invalid usernames in PAM

keyboard-interactive authentication (backported from a patch by Darren
Tucker; closes: #281595).

3 files changed, 17 insertions, 8 deletions

diff --git a/auth-pam.c b/auth-pam.c
index 701d85b64..ec3b74951 100644
--- a/auth-pam.c
+++ b/auth-pam.c
@@ -169,6 +169,7 @@ static int sshpam_cred_established = 0;
 static int sshpam_account_status = -1;
 static char **sshpam_env = NULL;
 static Authctxt *sshpam_authctxt = NULL;
+static char badpw[] = "\b\n\r\177INCORRECT";
 
 /* Some PAM implementations don't implement this */
 #ifndef HAVE_PAM_GETENVLIST
@@ -644,7 +645,10 @@ sshpam_respond(void *ctx, u_int num, char **resp)
                 return (-1);
         }
         buffer_init(&buffer);
-        buffer_put_cstring(&buffer, *resp);
+        if (sshpam_authctxt->valid)
+                buffer_put_cstring(&buffer, *resp);
+        else
+                buffer_put_cstring(&buffer, badpw);
         if (ssh_msg_send(ctxt->pam_psock, PAM_AUTHTOK, &buffer) == -1) {
                 buffer_free(&buffer);
                 return (-1);
diff --git a/auth2-chall.c b/auth2-chall.c
index aacbf0bcc..0f08b05c6 100644
--- a/auth2-chall.c
+++ b/auth2-chall.c
@@ -275,12 +275,9 @@ input_userauth_info_response(int type, u_int32_t seq, void *ctxt)
         }
         packet_check_eom();
 
-        if (authctxt->valid) {
-                res = kbdintctxt->device->respond(kbdintctxt->ctxt,
-                    nresp, response);
-        } else {
-                res = -1;
-        }
+        res = kbdintctxt->device->respond(kbdintctxt->ctxt, nresp, response);
+        if (!authctxt->valid)
+                res = 1;        /* keep going if login invalid */
 
         for (i = 0; i < nresp; i++) {
                 memset(response[i], 'r', strlen(response[i]));
@@ -292,7 +289,7 @@ input_userauth_info_response(int type, u_int32_t seq, void *ctxt)
         switch (res) {
         case 0:
                 /* Success! */
-                authenticated = 1;
+                authenticated = authctxt->valid ? 1 : 0;
                 break;
         case 1:
                 /* Authentication needs further interaction */
diff --git a/debian/changelog b/debian/changelog
index 4a53bef7e..8693c48ef 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -1,3 +1,11 @@
+openssh (1:3.8.1p1-8.sarge.4) UNRELEASED; urgency=high
+
+  * Fix timing information leak allowing discovery of invalid usernames in
+    PAM keyboard-interactive authentication (backported from a patch by
+    Darren Tucker; closes: #281595).
+
+ -- Colin Watson <cjwatson@debian.org>  Sun, 28 Nov 2004 12:12:55 +0000
+
 openssh (1:3.8.1p1-8.sarge.3) unstable; urgency=low
 
   * Enable threading for PAM, on Sam Hartman's advice (closes: #278394).