The EU and US mostly agree on severity. Here is why it looks like they don’t.

What is actually going on

• The EU adopts the vendor’s score. 79% of EU scores match, exactly, the score the assigning authority (the CNA) supplied, which NVD stores as a “Secondary” metric. There is no independent European re-rating step.
• NVD has mostly stopped scoring too. NVD publishes its own “Primary” score for only 35% of these CVEs; the rest carry only the CNA’s score, which both databases pass through.
• The gap is CVSS 4.0 versus 3.1. The EUVD surfaces the newer 4.0 score; most tooling compares against 3.1. Across 12,256 CVEs scored in both, 4.0 is the lower number 58% of the time, about 0.5 points below 3.1 on average. That is the whole “downgrade.”
• Compare like for like and the disagreement collapses to about 7%, almost all of it the EU sitting a notch higher (6%), not lower (0.7%).