diff --git a/requirements.txt b/requirements.txt
index 85cdf268b..ad4f1d267 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -36,4 +36,5 @@ MarkupSafe==2.0.1
 # TODO: needed by some plugins: migrate
 simple_logger
 matplotlib
-validators
\ No newline at end of file
+validators
+tornado>=6.3.2 # not directly required, pinned by Snyk to avoid a vulnerability
\ No newline at end of file