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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
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')
-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 8577cbd8a..8913bb81a 100644
--- a/openbsd-compat/xcrypt.c
+++ b/openbsd-compat/xcrypt.c
@@ -25,6 +25,7 @@
25#include "includes.h" 25#include "includes.h"
26 26
27#include <sys/types.h> 27#include <sys/types.h>
28#include <string.h>
28#include <unistd.h> 29#include <unistd.h>
29#include <pwd.h> 30#include <pwd.h>
30 31
@@ -62,11 +63,44 @@
62# define crypt DES_crypt 63# define crypt DES_crypt
63# endif 64# endif
64 65
66/*
67 * Pick an appropriate password encryption type and salt for the running
68 * system.
69 */
70static const char *
71pick_salt(void)
72{
73 struct passwd *pw;
74 char *passwd, *p;
75 size_t typelen;
76 static char salt[32];
77
78 if (salt[0] != '\0')
79 return salt;
80 strlcpy(salt, "xx", sizeof(salt));
81 if ((pw = getpwuid(0)) == NULL)
82 return salt;
83 passwd = shadow_pw(pw);
84 if (passwd[0] != '$' || (p = strrchr(passwd + 1, '$')) == NULL)
85 return salt; /* no $, DES */
86 typelen = p - passwd + 1;
87 strlcpy(salt, passwd, MIN(typelen, sizeof(salt)));
88 explicit_bzero(passwd, strlen(passwd));
89 return salt;
90}
91
65char * 92char *
66xcrypt(const char *password, const char *salt) 93xcrypt(const char *password, const char *salt)
67{ 94{
68 char *crypted; 95 char *crypted;
69 96
97 /*
98 * If we don't have a salt we are encrypting a fake password for
99 * for timing purposes. Pick an appropriate salt.
100 */
101 if (salt == NULL)
102 salt = pick_salt();
103
70# ifdef HAVE_MD5_PASSWORDS 104# ifdef HAVE_MD5_PASSWORDS
71 if (is_md5_salt(salt)) 105 if (is_md5_salt(salt))
72 crypted = md5_crypt(password, salt); 106 crypted = md5_crypt(password, salt);