Fix regext substring capture variables for null matches. Bug 2933

broken-by: 59d66fdc13f0

3 files changed, 6 insertions, 1 deletions

diff --git a/src/src/exim.c b/src/src/exim.c
index b3fd9eff0..47a685aa7 100644
--- a/src/src/exim.c
+++ b/src/src/exim.c
@@ -134,6 +134,8 @@ if ((yield = (res >= 0)))
     PCRE2_SIZE len;
     pcre2_substring_get_bynumber(md, matchnum,
       (PCRE2_UCHAR **)&expand_nstring[expand_nmax], &len);
+    if (!expand_nstring[expand_nmax])
+      { expand_nstring[expand_nmax] = US""; len = 0; }
     expand_nlength[expand_nmax++] = (int)len;
     }
   expand_nmax--;
diff --git a/src/src/malware.c b/src/src/malware.c
index 8b5ec27c4..423a5b692 100644
--- a/src/src/malware.c
+++ b/src/src/malware.c
@@ -314,7 +314,10 @@ PCRE2_UCHAR * substr = NULL;
 PCRE2_SIZE slen;
 
 if (i >= 2)				/* Got it */
+  {
   pcre2_substring_get_bynumber(md, 1, &substr, &slen);	/* uses same ctx as md */
+  if (!substr) substr = US"";
+  }
 /* pcre2_match_data_free(md);	gen ctx needs no free */
 return US substr;
 }
diff --git a/src/src/regex.c b/src/src/regex.c
index 25496f950..b401ba0d7 100644
--- a/src/src/regex.c
+++ b/src/src/regex.c
@@ -82,7 +82,7 @@ for (pcre_list * ri = re_list_head; ri; ri = ri->next)
       PCRE2_UCHAR * cstr;
       PCRE2_SIZE cslen;
       pcre2_substring_get_bynumber(md, nn, &cstr, &cslen);	/* uses same ctx as md */
-      regex_vars[nn-1] = CUS cstr;
+      regex_vars[nn-1] = cstr ? CUS cstr : CUS"";
       }
 
     return OK;