Bypassing Web Cache Poisoning Countermeasures
Summary: PortSwigger researcher James Kettle published follow-up research showing that Cloudflare's two deployed defenses against web cache poisoning could be bypassed, because Cloudflare only inspects the first instance of each header, letting an attacker supply a duplicate header with a harmless first value and a payload in the second. The post also describes flawed patches elsewhere, including a WAF at www.tesla.com that blocked requests containing 'burpcollaborator.net' in any header and cached the block, and a target that whitelisted X-Forwarded-Host values without noticing the header can also populate request.port.
What you should know: Cloudflare's cache-key mitigation was bypassed through a single duplicate header, and the post notes it only ever covered the most popular headers, not cache poisoning in general. The Tesla example shows the failure mode a security leader should sit with: a block response that is itself cacheable turns a defense into a denial of service for every visitor who follows.
Read the original at PortSwigger Research ↗
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- Vulnerabilities & Patching
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