fix: anchor Klaviyo proxy endpoint allowlist to the full path shape - #11294
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The proxy's endpoint allowlist only checked the segment before the first slash, so a value like "template-universal-content/../lists" passed the check while the traversal segment let the request reach a Klaviyo endpoint that was never allowlisted. Replace the prefix check with a pattern anchored to the exact shape the app actually sends (an allowed endpoint, optionally followed by a single id segment), rejecting anything else outright.
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Michael Pineiro (michaelpineirocontentful)
added this pull request to stack #11296
September 9, 2026 20:53
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Summary
The Klaviyo proxy function's endpoint allowlist only checked the path segment before the first slash. A value like
template-universal-content/../listspassed that check, and the traversal segment let the request reach a Klaviyo API endpoint that was never allowlisted.Solution
Context
Third in a small stack of hardening fixes to the Klaviyo app found during a routine security review. Verified the new pattern still matches every endpoint value the frontend currently sends (bare endpoint names and
endpoint/{id}), while rejecting traversal and encoded-traversal variants.Test plan
tsc --noEmitpassesbuild-functions) succeeds