| name | web-cache-poisoning |
| description | Web cache poisoning & deception — get a shared cache to serve attacker content to other users, or trick it into caching victims' private pages. Load behind a CDN/cache (Cloudflare, Varnish, Fastly, Akamai), on unkeyed headers, `X-Forwarded-Host`, cache headers, or static-looking URLs. Signals: `Age`/`X-Cache` headers, CDN, reflected headers.
|
| domain | web |
| type | technique |
| stability | learning |
| modes | ["bugbounty"] |
| severity | high |
| owasp | ["A05:2021-Security-Misconfiguration"] |
| cwe | ["CWE-444","CWE-525"] |
| tools | ["burp","param-miner"] |
| schema_version | 1 |
Web cache poisoning & deception
When it applies
A shared cache (CDN/reverse proxy) sits in front of the app. Poisoning: an unkeyed input
influences the response but isn't part of the cache key, so your malicious response gets stored
and served to everyone. Deception: the cache is tricked into storing a victim's private page.
Why it works
Caches key on some request parts (URL, maybe some headers) and ignore others ("unkeyed"). If an
unkeyed header/param changes the response (reflected X-Forwarded-Host, a header-driven script
src), you poison the cached copy. Deception exploits path/extension rules that cache things that
shouldn't be cached.
Method
- Map cache behaviour:
X-Cache: hit/miss, Age, Cache-Control, CDN vendor. Send a
cache-buster param to test safely without poisoning the real key.
- Find unkeyed inputs with Burp Param Miner ("guess headers"):
X-Forwarded-Host,
X-Forwarded-Scheme, X-Host, custom headers reflected into the response.
- Poison (carefully): make the unkeyed input inject a payload (e.g.
X-Forwarded-Host: evil.com → a script/link src) that reflects into a cacheable response; confirm it's stored
and served to a clean request.
- Deception: request
/account.php/nonexistent.css — if the cache stores the private page
under the static-looking URL, another user can fetch victims' cached data.
Gotchas
- Test with a unique cache-buster so you don't poison production for real users; then prove one controlled hit.
- Impact = what the poisoned response does (XSS, redirect, defacement) × who receives it.
- CDNs normalize/strip headers differently — the win is a specific input this cache doesn't key on.
Verify success
A clean request (no attacker input) receives your poisoned response, or a victim's private page
is served from cache to you.
References
James Kettle "Practical Web Cache Poisoning"; PortSwigger cache labs; Param Miner.
