- Scott Cantor posted the bug report #2829955

  (http://curl.haxx.se/bug/view.cgi?id=2829955) mentioning the recent SSL cert
  verification flaw found and exploited by Moxie Marlinspike. The presentation
  he did at Black Hat is available here:
  https://www.blackhat.com/html/bh-usa-09/bh-usa-09-archives.html#Marlinspike

  Apparently at least one CA allowed a subjectAltName or CN that contain a
  zero byte, and thus clients that assumed they would never have zero bytes
  were exploited to OK a certificate that didn't actually match the site. Like
  if the name in the cert was "example.com\0theatualsite.com", libcurl would
  happily verify that cert for example.com.

  libcurl now better use the length of the extracted name, not assuming it is
  zero terminated.

1 files changed, 22 insertions, 11 deletions

diff --git a/lib/ssluse.c b/lib/ssluse.c
index ffc1fbd96..324b05d47 100644
--- a/lib/ssluse.c
+++ b/lib/ssluse.c
@@ -990,14 +990,19 @@ static int asn1_output(const ASN1_UTCTIME *tm,
 #define HOST_NOMATCH 0
 #define HOST_MATCH   1
 
-static int hostmatch(const char *hostname, const char *pattern)
+static int hostmatch(const char *hostname, const char *pattern, size_t plen)
 {
   while(1) {
     char c = *pattern++;
+    plen--;
 
-    if(c == '\0')
+    if(!plen)
       return (*hostname ? HOST_NOMATCH : HOST_MATCH);
 
+    if(!c)
+      /* an embedded zero in the pattern can't match a host name */
+      return HOST_NOMATCH;
+
     if(c == '*') {
       c = *pattern;
       if(c == '\0')      /* "*\0" matches anything remaining */
@@ -1005,7 +1010,7 @@ static int hostmatch(const char *hostname, const char *pattern)
 
       while(*hostname) {
         /* The only recursive function in libcurl! */
-        if(hostmatch(hostname++,pattern) == HOST_MATCH)
+        if(hostmatch(hostname++, pattern, plen) == HOST_MATCH)
           return HOST_MATCH;
       }
       break;
@@ -1018,17 +1023,20 @@ static int hostmatch(const char *hostname, const char *pattern)
 }
 
 static int
-cert_hostcheck(const char *match_pattern, const char *hostname)
+cert_hostcheck(const char *match_pattern, size_t mlen, const char *hostname)
 {
+  size_t hlen = strlen(hostname);
   if(!match_pattern || !*match_pattern ||
-      !hostname || !*hostname) /* sanity check */
+     !hostname || !*hostname) /* sanity check */
     return 0;
 
-  if(Curl_raw_equal(hostname, match_pattern)) /* trivial case */
+  if((hlen == mlen) && !memcmp(hostname, match_pattern, hlen))
+    /* trivial case */
     return 1;
 
-  if(hostmatch(hostname,match_pattern) == HOST_MATCH)
+  if(hostmatch(hostname, match_pattern, mlen) == HOST_MATCH)
     return 1;
+
   return 0;
 }
 
@@ -1101,7 +1109,7 @@ static CURLcode verifyhost(struct connectdata *conn,
       if(check->type == target) {
         /* get data and length */
         const char *altptr = (char *)ASN1_STRING_data(check->d.ia5);
-        size_t altlen;
+        size_t altlen = (size_t) ASN1_STRING_length(check->d.ia5);
 
         switch(target) {
         case GEN_DNS: /* name/pattern comparison */
@@ -1114,15 +1122,17 @@ static CURLcode verifyhost(struct connectdata *conn,
              Gisle researched the OpenSSL sources:
              "I checked the 0.9.6 and 0.9.8 sources before my patch and
              it always 0-terminates an IA5String."
+
+             To reduce the risk of an embedded zero before the final zero
+             causing us trouble, we use the length OpenSSL reports!
           */
-          if(cert_hostcheck(altptr, conn->host.name))
+          if(cert_hostcheck(altptr, altlen, conn->host.name))
             matched = TRUE;
           break;
 
         case GEN_IPADD: /* IP address comparison */
           /* compare alternative IP address if the data chunk is the same size
              our server IP address is */
-          altlen = (size_t) ASN1_STRING_length(check->d.ia5);
           if((altlen == addrlen) && !memcmp(altptr, &addr, altlen))
             matched = TRUE;
           break;
@@ -1196,7 +1206,8 @@ static CURLcode verifyhost(struct connectdata *conn,
             "SSL: unable to obtain common name from peer certificate");
       return CURLE_PEER_FAILED_VERIFICATION;
     }
-    else if(!cert_hostcheck((const char *)peer_CN, conn->host.name)) {
+    else if(!cert_hostcheck((const char *)peer_CN, strlen((char *)peer_CN),
+                            conn->host.name)) {
       if(data->set.ssl.verifyhost > 1) {
         failf(data, "SSL: certificate subject name '%s' does not match "
               "target host name '%s'", peer_CN, conn->host.dispname);