dropbear: backport upstream fix for CVE-2018-15599
CVE description : The recv_msg_userauth_request function in svr-auth.c in Dropbear through 2018.76 is prone to a user enumeration vulnerability because username validity affects how fields in SSH_MSG_USERAUTH messages are handled, a similar issue to CVE-2018-15473 in an unrelated codebase. Signed-off-by: Hans Dedecker <dedeckeh@gmail.com>
This commit is contained in:
Hans Dedecker
parent
bbe2cf657c
commit
2211ee0037
3 changed files with 224 additions and 3 deletions
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@ -9,7 +9,7 @@ include $(TOPDIR)/rules.mk
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PKG_NAME:=dropbear
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PKG_NAME:=dropbear
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PKG_VERSION:=2017.75
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PKG_VERSION:=2017.75
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PKG_RELEASE:=6
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PKG_RELEASE:=7
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PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.bz2
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PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.bz2
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PKG_SOURCE_URL:= \
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PKG_SOURCE_URL:= \
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@ -0,0 +1,221 @@
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From 52adbb34c32d3e2e1bcdb941e20a6f81138b8248 Mon Sep 17 00:00:00 2001
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From: Matt Johnston <matt@ucc.asn.au>
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Date: Thu, 23 Aug 2018 23:43:12 +0800
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Subject: [PATCH 2/2] Wait to fail invalid usernames
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---
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auth.h | 6 +++---
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svr-auth.c | 19 +++++--------------
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svr-authpam.c | 26 ++++++++++++++++++++++----
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svr-authpasswd.c | 27 ++++++++++++++-------------
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svr-authpubkey.c | 11 ++++++++++-
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5 files changed, 54 insertions(+), 35 deletions(-)
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--- a/auth.h
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+++ b/auth.h
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@@ -37,9 +37,9 @@ void recv_msg_userauth_request(void);
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void send_msg_userauth_failure(int partial, int incrfail);
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void send_msg_userauth_success(void);
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void send_msg_userauth_banner(buffer *msg);
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-void svr_auth_password(void);
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-void svr_auth_pubkey(void);
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-void svr_auth_pam(void);
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+void svr_auth_password(int valid_user);
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+void svr_auth_pubkey(int valid_user);
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+void svr_auth_pam(int valid_user);
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#ifdef ENABLE_SVR_PUBKEY_OPTIONS
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int svr_pubkey_allows_agentfwd(void);
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--- a/svr-auth.c
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+++ b/svr-auth.c
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@@ -176,10 +176,8 @@ void recv_msg_userauth_request() {
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if (methodlen == AUTH_METHOD_PASSWORD_LEN &&
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strncmp(methodname, AUTH_METHOD_PASSWORD,
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AUTH_METHOD_PASSWORD_LEN) == 0) {
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- if (valid_user) {
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- svr_auth_password();
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- goto out;
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- }
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+ svr_auth_password(valid_user);
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+ goto out;
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}
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}
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#endif
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@@ -191,10 +189,8 @@ void recv_msg_userauth_request() {
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if (methodlen == AUTH_METHOD_PASSWORD_LEN &&
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strncmp(methodname, AUTH_METHOD_PASSWORD,
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AUTH_METHOD_PASSWORD_LEN) == 0) {
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- if (valid_user) {
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- svr_auth_pam();
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- goto out;
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- }
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+ svr_auth_pam(valid_user);
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+ goto out;
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}
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}
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#endif
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@@ -204,12 +200,7 @@ void recv_msg_userauth_request() {
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if (methodlen == AUTH_METHOD_PUBKEY_LEN &&
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strncmp(methodname, AUTH_METHOD_PUBKEY,
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AUTH_METHOD_PUBKEY_LEN) == 0) {
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- if (valid_user) {
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- svr_auth_pubkey();
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- } else {
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- /* pubkey has no failure delay */
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- send_msg_userauth_failure(0, 0);
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- }
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+ svr_auth_pubkey(valid_user);
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goto out;
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}
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#endif
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--- a/svr-authpam.c
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+++ b/svr-authpam.c
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@@ -178,13 +178,14 @@ pamConvFunc(int num_msg,
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* Keyboard interactive would be a lot nicer, but since PAM is synchronous, it
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* gets very messy trying to send the interactive challenges, and read the
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* interactive responses, over the network. */
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-void svr_auth_pam() {
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+void svr_auth_pam(int valid_user) {
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struct UserDataS userData = {NULL, NULL};
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struct pam_conv pamConv = {
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pamConvFunc,
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&userData /* submitted to pamvConvFunc as appdata_ptr */
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};
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+ const char* printable_user = NULL;
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pam_handle_t* pamHandlep = NULL;
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@@ -204,12 +205,23 @@ void svr_auth_pam() {
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password = buf_getstring(ses.payload, &passwordlen);
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+ /* We run the PAM conversation regardless of whether the username is valid
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+ in case the conversation function has an inherent delay.
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+ Use ses.authstate.username rather than ses.authstate.pw_name.
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+ After PAM succeeds we then check the valid_user flag too */
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+
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/* used to pass data to the PAM conversation function - don't bother with
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* strdup() etc since these are touched only by our own conversation
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* function (above) which takes care of it */
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- userData.user = ses.authstate.pw_name;
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+ userData.user = ses.authstate.username;
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userData.passwd = password;
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+ if (ses.authstate.pw_name) {
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+ printable_user = ses.authstate.pw_name;
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+ } else {
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+ printable_user = "<invalid username>";
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+ }
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+
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/* Init pam */
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if ((rc = pam_start("sshd", NULL, &pamConv, &pamHandlep)) != PAM_SUCCESS) {
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dropbear_log(LOG_WARNING, "pam_start() failed, rc=%d, %s",
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@@ -236,7 +248,7 @@ void svr_auth_pam() {
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rc, pam_strerror(pamHandlep, rc));
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dropbear_log(LOG_WARNING,
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"Bad PAM password attempt for '%s' from %s",
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- ses.authstate.pw_name,
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+ printable_user,
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svr_ses.addrstring);
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send_msg_userauth_failure(0, 1);
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goto cleanup;
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@@ -247,12 +259,18 @@ void svr_auth_pam() {
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rc, pam_strerror(pamHandlep, rc));
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dropbear_log(LOG_WARNING,
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"Bad PAM password attempt for '%s' from %s",
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- ses.authstate.pw_name,
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+ printable_user,
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svr_ses.addrstring);
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send_msg_userauth_failure(0, 1);
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goto cleanup;
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}
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+ if (!valid_user) {
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+ /* PAM auth succeeded but the username isn't allowed in for another reason
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+ (checkusername() failed) */
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+ send_msg_userauth_failure(0, 1);
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+ }
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+
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/* successful authentication */
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dropbear_log(LOG_NOTICE, "PAM password auth succeeded for '%s' from %s",
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ses.authstate.pw_name,
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--- a/svr-authpasswd.c
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+++ b/svr-authpasswd.c
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@@ -48,22 +48,14 @@ static int constant_time_strcmp(const ch
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/* Process a password auth request, sending success or failure messages as
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* appropriate */
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-void svr_auth_password() {
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+void svr_auth_password(int valid_user) {
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char * passwdcrypt = NULL; /* the crypt from /etc/passwd or /etc/shadow */
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char * testcrypt = NULL; /* crypt generated from the user's password sent */
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- char * password;
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+ char * password = NULL;
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unsigned int passwordlen;
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-
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unsigned int changepw;
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- passwdcrypt = ses.authstate.pw_passwd;
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-
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-#ifdef DEBUG_HACKCRYPT
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- /* debugging crypt for non-root testing with shadows */
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- passwdcrypt = DEBUG_HACKCRYPT;
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-#endif
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-
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/* check if client wants to change password */
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changepw = buf_getbool(ses.payload);
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if (changepw) {
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@@ -73,12 +65,21 @@ void svr_auth_password() {
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}
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password = buf_getstring(ses.payload, &passwordlen);
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-
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- /* the first bytes of passwdcrypt are the salt */
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- testcrypt = crypt(password, passwdcrypt);
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+ if (valid_user) {
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+ /* the first bytes of passwdcrypt are the salt */
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+ passwdcrypt = ses.authstate.pw_passwd;
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+ testcrypt = crypt(password, passwdcrypt);
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+ }
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m_burn(password, passwordlen);
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m_free(password);
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+ /* After we have got the payload contents we can exit if the username
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+ is invalid. Invalid users have already been logged. */
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+ if (!valid_user) {
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+ send_msg_userauth_failure(0, 1);
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+ return;
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+ }
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+
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if (testcrypt == NULL) {
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/* crypt() with an invalid salt like "!!" */
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dropbear_log(LOG_WARNING, "User account '%s' is locked",
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--- a/svr-authpubkey.c
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+++ b/svr-authpubkey.c
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@@ -79,7 +79,7 @@ static int checkfileperm(char * filename
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/* process a pubkey auth request, sending success or failure message as
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* appropriate */
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-void svr_auth_pubkey() {
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+void svr_auth_pubkey(int valid_user) {
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unsigned char testkey; /* whether we're just checking if a key is usable */
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char* algo = NULL; /* pubkey algo */
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@@ -102,6 +102,15 @@ void svr_auth_pubkey() {
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keybloblen = buf_getint(ses.payload);
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keyblob = buf_getptr(ses.payload, keybloblen);
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+ if (!valid_user) {
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+ /* Return failure once we have read the contents of the packet
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+ required to validate a public key.
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+ Avoids blind user enumeration though it isn't possible to prevent
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+ testing for user existence if the public key is known */
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+ send_msg_userauth_failure(0, 0);
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+ goto out;
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+ }
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+
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/* check if the key is valid */
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if (checkpubkey(algo, algolen, keyblob, keybloblen) == DROPBEAR_FAILURE) {
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send_msg_userauth_failure(0, 0);
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@ -1,6 +1,6 @@
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--- a/svr-authpubkey.c
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--- a/svr-authpubkey.c
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+++ b/svr-authpubkey.c
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+++ b/svr-authpubkey.c
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@@ -220,14 +220,20 @@ static int checkpubkey(char* algo, unsig
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@@ -229,14 +229,20 @@ static int checkpubkey(char* algo, unsig
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goto out;
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goto out;
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}
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}
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@ -29,7 +29,7 @@
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/* open the file as the authenticating user. */
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/* open the file as the authenticating user. */
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origuid = getuid();
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origuid = getuid();
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@@ -396,26 +402,35 @@ static int checkpubkeyperms() {
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@@ -405,26 +411,35 @@ static int checkpubkeyperms() {
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goto out;
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goto out;
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}
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}
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