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authorDarren Tucker <dtucker@zip.com.au>2016-07-15 13:32:45 +1000
committerDarren Tucker <dtucker@zip.com.au>2016-07-15 13:45:42 +1000
commit9286875a73b2de7736b5e50692739d314cd8d9dc (patch)
treeda8bbecb3d639077b3ca94d31f0e94253009b061 /openbsd-compat/xcrypt.c
parenta162dd5e58ca5b224d7500abe35e1ef32b5de071 (diff)
Determine appropriate salt for invalid users.
When sshd is processing a non-PAM login for a non-existent user it uses the string from the fakepw structure as the salt for crypt(3)ing the password supplied by the client. That string has a Blowfish prefix, so on systems that don't understand that crypt will fail fast due to an invalid salt, and even on those that do it may have significantly different timing from the hash methods used for real accounts (eg sha512). This allows user enumeration by, eg, sending large password strings. This was noted by EddieEzra.Harari at verint.com (CVE-2016-6210). To mitigate, use the same hash algorithm that root uses for hashing passwords for users that do not exist on the system. ok djm@
Diffstat (limited to 'openbsd-compat/xcrypt.c')
-rw-r--r--openbsd-compat/xcrypt.c34
1 files changed, 34 insertions, 0 deletions
diff --git a/openbsd-compat/xcrypt.c b/openbsd-compat/xcrypt.c
index 8577cbd8..8913bb81 100644
--- a/openbsd-compat/xcrypt.c
+++ b/openbsd-compat/xcrypt.c
@@ -25,6 +25,7 @@
#include "includes.h"
#include <sys/types.h>
+#include <string.h>
#include <unistd.h>
#include <pwd.h>
@@ -62,11 +63,44 @@
# define crypt DES_crypt
# endif
+/*
+ * Pick an appropriate password encryption type and salt for the running
+ * system.
+ */
+static const char *
+pick_salt(void)
+{
+ struct passwd *pw;
+ char *passwd, *p;
+ size_t typelen;
+ static char salt[32];
+
+ if (salt[0] != '\0')
+ return salt;
+ strlcpy(salt, "xx", sizeof(salt));
+ if ((pw = getpwuid(0)) == NULL)
+ return salt;
+ passwd = shadow_pw(pw);
+ if (passwd[0] != '$' || (p = strrchr(passwd + 1, '$')) == NULL)
+ return salt; /* no $, DES */
+ typelen = p - passwd + 1;
+ strlcpy(salt, passwd, MIN(typelen, sizeof(salt)));
+ explicit_bzero(passwd, strlen(passwd));
+ return salt;
+}
+
char *
xcrypt(const char *password, const char *salt)
{
char *crypted;
+ /*
+ * If we don't have a salt we are encrypting a fake password for
+ * for timing purposes. Pick an appropriate salt.
+ */
+ if (salt == NULL)
+ salt = pick_salt();
+
# ifdef HAVE_MD5_PASSWORDS
if (is_md5_salt(salt))
crypted = md5_crypt(password, salt);