telnet: fix option parser to not send uninitialized contents

CVS-2021-22925

Reported-by: Red Hat Product Security
Bug: https://curl.se/docs/CVE-2021-22925.html

diff --git a/lib/telnet.c b/lib/telnet.c
index 1d3024ec4d3ec4534f084cff88ce5349026d80b8..a81bb81c3675ac47fa5b94c1e16bd49ca27d2db5 100644 (file)
--- a/lib/telnet.c
+++ b/lib/telnet.c
@@ -920,12 +920,17 @@ static void suboption(struct Curl_easy *data)
         size_t tmplen = (strlen(v->data) + 1);
         /* Add the variable only if it fits */
         if(len + tmplen < (int)sizeof(temp)-6) {
-          if(sscanf(v->data, "%127[^,],%127s", varname, varval) == 2) {
-            msnprintf((char *)&temp[len], sizeof(temp) - len,
-                      "%c%s%c%s", CURL_NEW_ENV_VAR, varname,
-                      CURL_NEW_ENV_VALUE, varval);
-            len += tmplen;
-          }
+          int rv;
+          char sep[2] = "";
+          varval[0] = 0;
+          rv = sscanf(v->data, "%127[^,]%1[,]%127s", varname, sep, varval);
+          if(rv == 1)
+            len += msnprintf((char *)&temp[len], sizeof(temp) - len,
+                             "%c%s", CURL_NEW_ENV_VAR, varname);
+          else if(rv >= 2)
+            len += msnprintf((char *)&temp[len], sizeof(temp) - len,
+                             "%c%s%c%s", CURL_NEW_ENV_VAR, varname,
+                             CURL_NEW_ENV_VALUE, varval);
         }
       }
       msnprintf((char *)&temp[len], sizeof(temp) - len,