Due to a known PHP-issue (see RegExp "Known Issues") a "simple" preg_match call may crash PHP-execution. So far, this only happened in the function validateQuery() of class Zend_Uri_Http (indirectly) used by the Zend_Http_Client when (over)long URL-queries were generated.

Workaround: reduce pcre.recursion_limit to a safe level for this call

--- library/Zend/Uri/Http.php   (revision 22559)
+++ library/Zend/Uri/Http.php   (working copy)
@@ -630,7 +630,34 @@
 
         // Determine whether the query is well-formed
         $pattern = '/^' . $this->_regex['uric'] . '*$/';
+
+   // ======================================================================
+   // added in order to fix Segmentation Fault problem that may appear 
+   // on (over)long URLs with long URL-encoded parameters
+   // trying to catch a PHP-bug by decreasing backtracking- and recursion-limits ...
+   // ======================================================================
+
+   // decrease the PCRE recursion limit for the (possibly dangerous) preg_match call
+   $former_recursion_limit = ini_set("pcre.recursion_limit", 10000);
+
+   // the original call to pregmatch
         $status  = @preg_match($pattern, $query);
+
+   // reset the PCRE recursion limit to its original value
+   ini_set("pcre.recursion_limit", $former_recursion_limit);
+
+   // if the reg-exp has failed to our decreased recursion limit we (Zend) can not make
+   // any statement over the validity of the query and has to assume validity ;)
+   if (PREG_RECURSION_LIMIT_ERROR == preg_last_error()) {
+       $status = true;
+           require_once 'Zend/Uri/Exception.php';
+           throw new Zend_Uri_Exception("Zend_Uri_Http validateQuery check regular expression fails due to decreased PCRE recursion limit (preventing a possible C-Segmentation Fault). Query: $query" );
+   }
+
+   // ======================================================================
+   // END OF MODIFICATION
+   // ======================================================================
+
         if ($status === false) {
             require_once 'Zend/Uri/Exception.php';
             throw new Zend_Uri_Exception('Internal error: query validation failed');