Harden client IP resolution in RateLimitMiddleware - #19567
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Follow-up to the ipHeader default change: - Extract the left-most entry from a forwarded chain again. Using the raw header line keyed the limit on the whole "client, proxy1, ..." string, so an attacker could vary downstream hops to bypass the limit. - Handle the 'remote_addr' default explicitly instead of relying on it not matching any header name and falling through. - Document that forwarded headers are spoofable and only safe when a trusted proxy overwrites them. - Assert the resolved identifier in the trust-proxy test and switch the status assertions to assertSame(200, ...).
markstory
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Jul 27, 2026
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Thanks for catching the mistake I had with remote_addr ❤️ |
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The previous defaults were not safe, and I don't think we should have released this like this. I've also cleaned up some of the implementation as ServerRequestInterface has methods for this. Thank you to `@yousukezan` for reporting this issue through our security mailing list. * Harden client IP resolution in RateLimitMiddleware (#19567) - Extract the left-most entry from a forwarded chain again. Using the raw header line keyed the limit on the whole "client, proxy1, ..." string, so an attacker could vary downstream hops to bypass the limit. - Handle the 'remote_addr' default explicitly instead of relying on it not matching any header name and falling through. - Document that forwarded headers are spoofable and only safe when a trusted proxy overwrites them. - Assert the resolved identifier in the trust-proxy test and switch the status assertions to assertSame(200, ...). --------- Co-authored-by: Kevin Pfeifer <[email protected]> Co-authored-by: othercorey <[email protected]> Co-authored-by: Mark Scherer <[email protected]>
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Follow-up to #19565, targeting that branch.
The default change from
x-forwarded-fortoremote_addris the right fix. This adds three hardening/correctness follow-ups on top of it.1. Restore left-most IP extraction (behavior regression)
#19565 replaced the
explode(',', ...)+trim($ips[0])extraction with the rawgetHeaderLine()value. For anyone opting back intoipHeader => 'x-forwarded-for', the rate-limit identifier became the entire forwarded chain (192.168.1.101, 10.0.0.1) instead of the client IP.That is a bypass: an attacker who controls XFF can vary the downstream hops (
client, junk1,client, junk2, ...) and get a fresh key each request. This restores taking the left-most (originating client) entry.2. Explicit
remote_addrhandlingThe new default only worked because
getHeaderLine('remote_addr')returns''and falls through to$params['REMOTE_ADDR']. That is implicit - any nonexistent header name behaves the same. Handle theremote_addrsentinel explicitly so intent is clear.3. Docs + tests
testProxyHeadersWithTrustProxynow asserts the resolved identifier: it primes on client192.168.1.101via the chain, then re-requests with the same client but a different proxy hop and asserts the limit is hit. The previous version only asserted200twice and would have passed even with the chain-keying bug.assertSame(200, ...)(expected-first, type-strict).Gates:
RateLimitMiddlewareTest10/10 green, phpstan clean, phpcs clean.