diff --git a/changes/bug40316 b/changes/bug40316
new file mode 100644
index 0000000000..cd275b5c9c
--- /dev/null
+++ b/changes/bug40316
@@ -0,0 +1,5 @@
+  o Major bugfixes (security, denial of service):
+    - Fix a bug in appending detached signatures to a pending consensus
+      document that could be used to crash a directory authority.
+      Fixes bug 40316; bugfix on 0.2.2.6-alpha. Tracked as
+      TROVE-2021-002 and CVE-2021-28090.
diff --git a/src/feature/dirauth/dirvote.c b/src/feature/dirauth/dirvote.c
index 4b9cb9f9f3..ffaa78b997 100644
--- a/src/feature/dirauth/dirvote.c
+++ b/src/feature/dirauth/dirvote.c
@@ -3610,7 +3610,7 @@ dirvote_add_signatures_to_pending_consensus(
       strlen(pc->body) + strlen(new_signatures) + 1;
     pc->body = tor_realloc(pc->body, new_consensus_len);
     dst_end = pc->body + new_consensus_len;
-    dst = strstr(pc->body, "directory-signature ");
+    dst = (char *) find_str_at_start_of_line(pc->body, "directory-signature ");
     tor_assert(dst);
     strlcpy(dst, new_signatures, dst_end-dst);