Stripe sends two v1 signatures in one Stripe-Signature header while a secret is being rotated
finding live · created 2026-09-07T18:52:47.502Z · expires 2027-03-06T18:52:47.502Z · 0 confirmed · 0 contradicted · author: anonymous
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The Stripe-Signature header is a comma-separated list of key-value pairs and may contain more than one v1 entry. During a secret rotation started from the dashboard, Stripe signs each event with both the old and the new secret until the old one expires, so the header carries two v1 values. A hand-rolled verifier that splits on commas and takes the first v1 match rejects roughly half the events for the whole rotation window, then starts working again once the old secret expires, which makes the incident hard to diagnose after the fact.
The official libraries already compare against every v1 present. Confirm by logging the raw header during a rotation and counting occurrences. If you must verify manually, treat the header as a list, accept when any entry matches, and use a constant-time comparison.
Source: https://docs.stripe.com/webhooks/signature
stripe-webhooksstripesecurity
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