Lighttpd

Yes, there is a real "memory leak" in lighttpd.

I was able to recreate the leaking behaviour on an x86_64 desktop.
Attached is a valgrind log clearly showing unreachable bytes.

Further inspection of the mod_authn_ldap.c shows the incorrect function for freeing variables of type LDAP*

ldap_destroy() must be used instead of ldap_memfree() to free types of LDAP*

eg

The way to trigger the leak is to just repeatedly try to login with bad credentials.
Please patch immediately on your end as this is a vulnerability on internal systems.

(I doubt anyone would use ldap on an internet facing system, I could be wrong)

Thank you for the trace. Something is definitely amiss.
'man ldap_destroy' instructs

       When ldap_unbind() is called on a session handle with siblings, all the
       siblings become invalid.

       Siblings  must  be  destroyed  using  ldap_destroy().   Session  handle
       resources  associated with the original (LDAP *) will be freed when the
       last session handle is destroyed or when ldap_unbind() is called, if no
       other session handles currently exist.

Untested, but here is the 5 min patch to call ldap_destroy() (instead of ldap_memfree()) after a successful ldap_initialize(), even if the ldap_sasl_bind_s() fails.

diff --git a/src/mod_authn_ldap.c b/src/mod_authn_ldap.c
index c2e793d1..3e75cf10 100644
--- a/src/mod_authn_ldap.c
+++ b/src/mod_authn_ldap.c
@@ -398,7 +398,7 @@ static LDAP * mod_authn_ldap_host_init(server *srv, plugin_c
onfig *s) {
     ret = ldap_set_option(ld, LDAP_OPT_PROTOCOL_VERSION, &ret);
     if (LDAP_OPT_SUCCESS != ret) {
         mod_authn_ldap_err(srv, __FILE__, __LINE__, "ldap_set_options()", ret);
-        ldap_memfree(ld);
+        ldap_destroy(ld);
         return NULL;
     }

@@ -412,7 +412,7 @@ static LDAP * mod_authn_ldap_host_init(server *srv, plugin_c
onfig *s) {
                 mod_authn_ldap_err(srv, __FILE__, __LINE__,
                                    "ldap_set_option(LDAP_OPT_X_TLS_CACERTFILE)" 
,
                                    ret);
-                ldap_memfree(ld);
+                ldap_destroy(ld);
                 return NULL;
             }
         }
@@ -420,7 +420,7 @@ static LDAP * mod_authn_ldap_host_init(server *srv, plugin_c
onfig *s) {
         ret = ldap_start_tls_s(ld, NULL,  NULL);
         if (LDAP_OPT_SUCCESS != ret) {
             mod_authn_ldap_err(srv,__FILE__,__LINE__,"ldap_start_tls_s()",ret);
-            ldap_memfree(ld);
+            ldap_destroy(ld);
             return NULL;
         }
     }
@@ -490,7 +490,7 @@ static LDAPMessage * mod_authn_ldap_search(server *srv, plugin_config *s, char *
                             s->auth_ldap_bindpw->ptr)
       : mod_authn_ldap_bind(srv, s->ldap, NULL, NULL);
     if (LDAP_SUCCESS != ret) {
-        ldap_memfree(s->ldap);
+        ldap_destroy(s->ldap);
         s->ldap = NULL;
         return NULL;
     }
@@ -635,7 +635,7 @@ static handler_t mod_authn_ldap_basic(server *srv, connection *con, void *p_d, c
     }

     if (LDAP_SUCCESS != mod_authn_ldap_bind(srv, ld, dn, pw)) {
-        ldap_memfree(ld);
+        ldap_destroy(ld);
         if (dn != p->ldap_filter->ptr) ldap_memfree(dn);
         return HANDLER_ERROR;
     }
diff --git a/src/mod_vhostdb_ldap.c b/src/mod_vhostdb_ldap.c
index 459d7d60..4f7e2a5f 100644
--- a/src/mod_vhostdb_ldap.c
+++ b/src/mod_vhostdb_ldap.c
@@ -251,7 +251,7 @@ static LDAP * mod_authn_ldap_host_init(server *srv, vhostdb_config *s) {
     ret = ldap_set_option(ld, LDAP_OPT_PROTOCOL_VERSION, &ret);
     if (LDAP_OPT_SUCCESS != ret) {
         mod_authn_ldap_err(srv, __FILE__, __LINE__, "ldap_set_options()", ret);
-        ldap_memfree(ld);
+        ldap_destroy(ld);
         return NULL;
     }

@@ -264,7 +264,7 @@ static LDAP * mod_authn_ldap_host_init(server *srv, vhostdb_config *s) {
                 mod_authn_ldap_err(srv, __FILE__, __LINE__,
                                    "ldap_set_option(LDAP_OPT_X_TLS_CACERTFILE)",
                                    ret);
-                ldap_memfree(ld);
+                ldap_destroy(ld);
                 return NULL;
             }
         }
@@ -272,7 +272,7 @@ static LDAP * mod_authn_ldap_host_init(server *srv, vhostdb_config *s) {
         ret = ldap_start_tls_s(ld, NULL,  NULL);
         if (LDAP_OPT_SUCCESS != ret) {
             mod_authn_ldap_err(srv,__FILE__,__LINE__,"ldap_start_tls_s()",ret);
-            ldap_memfree(ld);
+            ldap_destroy(ld);
             return NULL;
         }
     }
@@ -338,7 +338,7 @@ static LDAPMessage * mod_authn_ldap_search(server *srv, vhostdb_config *s, char

     ret = mod_authn_ldap_bind(srv, s->ldap, s->binddn, s->bindpw);
     if (LDAP_SUCCESS != ret) {
-        ldap_memfree(s->ldap);
+        ldap_destroy(s->ldap);
         s->ldap = NULL;
         return NULL;
     }

Applied in changeset 37f9b60d5e09d000e836a905559326775c81831f.