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Spring Boot 4.1 introduced InetAddressFilter for restricting the IP addresses that outgoing HTTP clients may contact. Configure it on a client through HttpClientSettings, or expose a filter bean for auto-configured client builders. This is an address-level control—not a complete defense for every user-supplied URL, redirect, or HTTP client path.
Which Spring Boot versions support InetAddressFilter?
Spring Boot 4.1.0 introduced the feature; Spring announced that release on June 10, 2026. The configuration guidance is in the Spring Boot 4.1 reference, and the API documentation cited here is for Spring Boot 4.1.1. Do not assume the API is available in earlier Spring Boot versions. Spring’s release highlights say both reactive and blocking HTTP clients can be configured with an InetAddressFilter to block outgoing requests to selected addresses.
Spring Boot 4.1.0 release announcement · Spring Boot 4.1 reference: Calling REST Services · Spring Boot 4.1.1 InetAddressFilter API · Spring Boot 4.1 release highlights
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For a client with a specific destination policy, attach the filter to HttpClientSettings, build a JDK request factory with those settings, and give that factory to RestClient. Spring’s reference demonstrates this pattern with the built-in external-address policy:
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InetAddressFilter onlyExternalAddresses = InetAddressFilter.externalAddresses();
HttpClientSettings settings = HttpClientSettings.defaults()
.withInetAddressFilter(onlyExternalAddresses);
ClientHttpRequestFactory requestFactory = ClientHttpRequestFactoryBuilder.jdk()
.build(settings);
RestClient restClient = RestClient.builder()
.requestFactory(requestFactory)
.baseUrl("https://example.org")
.build();Use this per-client approach when clients in the same application need different destination rules. The filter is set on the request factory used by this RestClient; it does not, by itself, configure clients constructed elsewhere.
Spring Boot 4.1 reference: client configuration examples
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Configure a filter for auto-configured client builders
To provide a shared policy to auto-configured HTTP client builders, define an InetAddressFilter bean. This example permits the specified private IPv4 CIDR range except for two addresses:
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InetAddressFilter httpClientInetAddressFilter() {
return InetAddressFilter.of("192.168.1.0/24")
.andNot("192.168.1.1", "192.168.1.10");
}of matches the CIDR range, while andNot removes the listed addresses from that match. A bean is for auto-configured client builders; verify coverage in your application if code also creates clients manually or sends requests through other client libraries or paths.
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Spring Boot 4.1 reference: InetAddressFilter bean example
Choose a policy that matches your destinations
The API supports IPv4 and IPv6 addresses and CIDR blocks. Its factories and composition methods let you express broad address classes or combine more specific rules.
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| Policy or method | What it does |
|---|---|
externalAddresses() |
Matches addresses considered external by Spring’s filter. |
internalAddresses() |
Matches addresses considered internal by Spring’s filter. |
routable() |
Matches addresses considered routable by Spring’s filter. |
multicast() |
Matches multicast addresses. |
specialPurpose() |
Matches special-purpose addresses. |
of(...) |
Creates a filter from IPv4 or IPv6 addresses and CIDR blocks. |
and, or, andNot, negate |
Combine or invert address-matching rules. |
These methods evaluate addresses, not whether a URL is trustworthy as a whole. For example, allowing a private CIDR may be necessary when an application calls an internal service, but it also permits requests to matching addresses. Keep any exception as narrow as the actual service requirement.
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Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Harden the complete outbound request path
SSRF defenses should account for how a URL becomes a network connection. A hostname can resolve to an address during validation and a different address when the client connects. The USENIX Security 2024 paper describes this DNS rebinding problem and discusses IP pinning: resolve once and continue using the validated address. The paper also advises rejecting redirects or validating every redirect destination. These are general security principles; Spring’s cited reference does not establish identical DNS or redirect behavior for every underlying client and request flow.
- Allow only URL schemes your application needs, such as HTTPS, rather than accepting arbitrary schemes.
- Apply address filtering to every outbound client and code path that can handle attacker-influenced URLs.
- Decide whether redirects are needed. Reject them where practical, or validate each redirect target under the same policy.
- Confirm how the specific request factory and client resolve DNS and handle redirects; do not assume validation and connection use the same address without checking.
- Review internal-address exceptions against actual service needs, and keep permitted ranges and exclusions specific.
USENIX Security 2024: Server-Side Request Forgery: Theory and Practice
Do not confuse Spring Boot Admin settings with Spring Boot client defaults
Spring Boot Admin documents a separate SSRF protection feature. Its documentation says that protection is disabled by default in that product and describes allowing selected internal CIDRs when internal communication is required. Those are Spring Boot Admin-specific settings, not defaults for all Spring Boot HTTP clients or a substitute for configuring their outbound request paths.
Quick Recap
Spring Boot Admin 4.1.2: SSRF Protection
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