CVE-2026-111171

Web3.py 7.15.0 through 7.16.0 and 8.0.0b2 through 8.0.0 contains a server-side request forgery vulnerability because _check_ip_blocked() does not unwrap IPv4-mapped IPv6 addresses in CCIP Read URL validation. Malicious contracts can return OffchainLookup URLs with IPv4-mapped IPv6 hosts or AAAA records, making clients with CCIP Read enabled send requests to loopback, private, or link-local services.

Web3.py 7.15.0 through 7.16.0 and 8.0.0b2 through 8.0.0 contains a server-side request forgery vulnerability because _check_ip_blocked() does not unwrap IPv4-mapped IPv6 addresses in CCIP Read URL validation. Malicious contracts can return OffchainLookup URLs with IPv4-mapped IPv6 hosts or AAAA records, making clients with CCIP Read enabled send requests to loopback, private, or link-local services.

Web3.py 7.15.0 through 7.16.0 and 8.0.0b2 through 8.0.0 contains a server-side request forgery vulnerability because _check_ip_blocked() does not unwrap IPv4-mapped IPv6 addresses in CCIP Read URL validation. Malicious contracts can return OffchainLookup URLs with IPv4-mapped IPv6 hosts or AAAA records, making clients with CCIP Read enabled send requests to loopback, private, or link-local services.

Web3.py 7.15.0 through 7.16.0 and 8.0.0b2 through 8.0.0 contains a server-side request forgery vulnerability because _check_ip_blocked() does not unwrap IPv4-mapped IPv6 addresses in CCIP Read URL validation. Malicious contracts can return OffchainLookup URLs with IPv4-mapped IPv6 hosts or AAAA records, making clients with CCIP Read enabled send requests to loopback, private, or link-local services.

Web3.py 7.15.0 through 7.16.0 and 8.0.0b2 through 8.0.0 contains a server-side request forgery vulnerability because _check_ip_blocked() does not unwrap IPv4-mapped IPv6 addresses in CCIP Read URL validation. Malicious contracts can return OffchainLookup URLs with IPv4-mapped IPv6 hosts or AAAA records, making clients with CCIP Read enabled send requests to loopback, private, or link-local services.

web3.py allows you to interact with the Ethereum blockchain using Python. From 6.0.0b3 to before 7.15.0 and 8.0.0b2, web3.py implements CCIP Read / OffchainLookup (EIP-3668) by performing HTTP requests to URLs supplied by smart contracts in offchain_lookup_payload["urls"]. The implementation uses these contract-supplied URLs directly (after {sender} / {data} template substitution) without any destination validation. CCIP Read is enabled by default (global_ccip_read_enabled = True on all providers), meaning any application using web3.py's .call() method is exposed without explicit opt-in. This results in Server-Side Request Forgery (SSRF) when web3.py is used in backend services, indexers, APIs, or any environment that performs eth_call / .call() against untrusted or user-supplied contract addresses. A malicious contract can force the web3.py process to issue HTTP requests to arbitrary destinations, including internal network services and cloud metadata endpoints. This vulnerability is fixed in 7.15.0 and 8.0.0b2.

Summary

web3.py implements CCIP Read / OffchainLookup (EIP-3668) by performing HTTP requests to URLs supplied by smart contracts in offchain_lookup_payload["urls"]. The implementation uses these contract-supplied URLs directly (after {sender} / {data} template substitution) without any destination validation:

• No restriction to https:// (and no opt-in gate for http://)
• No hostname or IP allowlist
• No blocking of private/reserved IP ranges (loopback, link-local, RFC1918)
• No redirect target validation (both requests and aiohttp follow redirects by default)

CCIP Read is enabled by default (global_ccip_read_enabled = True on all providers), meaning any application using web3.py's .call() method is exposed without explicit opt-in.

This results in Server-Side Request Forgery (SSRF) when web3.py is used in backend services, indexers, APIs, or any environment that performs eth_call / .call() against untrusted or user-supplied contract addresses. A malicious contract can force the web3.py process to issue HTTP requests to arbitrary destinations, including internal network services and cloud metadata endpoints.

Why This Is a Vulnerability

The argument is not that CCIP Read itself is invalid or that web3.py should stop supporting EIP-3668. The issue is that, in server-side deployments (backends, indexers, bots, APIs), the current implementation doesn't provide destination policy controls, such as a validation/override hook, private-range blocking, or redirect target checks, which means contract controlled CCIP URLs can be used as an SSRF primitive.

This is consistent with EIP-3668's own security considerations, which recommends that client libraries "provide clients with a hook to override CCIP read calls, either by rewriting them to use a proxy service, or by denying them entirely" and that "this mechanism or another should be written so as to easily facilitate adding domains to allowlists or blocklists." The mitigations I'm suggesting are meant to align with that guidance without breaking CCIP Read support.

• Default-on exposure. CCIP Read is enabled by default on all web3.py providers (global_ccip_read_enabled = True). Users who never intend to use CCIP Read, and who may not even know the feature exists, are silently exposed. A feature that makes unsanitized outbound requests to attacker-controlled URLs should not be enabled by default without safety guardrails.

• Library vs. application responsibility. web3.py is a widely-used library. Expecting every downstream application to independently implement SSRF protections around .call() is unreasonable, especially for a feature that fires automatically and invisibly on a specific revert pattern. Safe defaults at the library level are the standard expectation for any library that issues outbound HTTP requests to externally-controlled URLs.

Affected Code

Sync CCIP handler

File: web3/utils/exception_handling.py (lines 42-58)

Contract-controlled URLs are requested via requests with no destination validation:

session = requests.Session()
for url in offchain_lookup_payload["urls"]:
    formatted_url = URI(
        str(url)
        .replace("{sender}", str(formatted_sender))
        .replace("{data}", str(formatted_data))
    )

    try:
        if "{data}" in url and "{sender}" in url:
            response = session.get(formatted_url, timeout=DEFAULT_HTTP_TIMEOUT)
        else:
            response = session.post(
                formatted_url,
                json={"data": formatted_data, "sender": formatted_sender},
                timeout=DEFAULT_HTTP_TIMEOUT,
            )

(The request is issued before response validation; subsequent logic parses JSON and enforces a "data" field.)

Key observations:

• requests follows redirects by default (allow_redirects=True).
• No allow_redirects=False is set.
• No validation of formatted_url before the request.
• The placeholder check…

Summary

web3.py implements CCIP Read / OffchainLookup (EIP-3668) by performing HTTP requests to URLs supplied by smart contracts in offchain_lookup_payload["urls"]. The implementation uses these contract-supplied URLs directly (after {sender} / {data} template substitution) without any destination validation:

• No restriction to https:// (and no opt-in gate for http://)
• No hostname or IP allowlist
• No blocking of private/reserved IP ranges (loopback, link-local, RFC1918)
• No redirect target validation (both requests and aiohttp follow redirects by default)

CCIP Read is enabled by default (global_ccip_read_enabled = True on all providers), meaning any application using web3.py's .call() method is exposed without explicit opt-in.

This results in Server-Side Request Forgery (SSRF) when web3.py is used in backend services, indexers, APIs, or any environment that performs eth_call / .call() against untrusted or user-supplied contract addresses. A malicious contract can force the web3.py process to issue HTTP requests to arbitrary destinations, including internal network services and cloud metadata endpoints.

Why This Is a Vulnerability

The argument is not that CCIP Read itself is invalid or that web3.py should stop supporting EIP-3668. The issue is that, in server-side deployments (backends, indexers, bots, APIs), the current implementation doesn't provide destination policy controls, such as a validation/override hook, private-range blocking, or redirect target checks, which means contract controlled CCIP URLs can be used as an SSRF primitive.

This is consistent with EIP-3668's own security considerations, which recommends that client libraries "provide clients with a hook to override CCIP read calls, either by rewriting them to use a proxy service, or by denying them entirely" and that "this mechanism or another should be written so as to easily facilitate adding domains to allowlists or blocklists." The mitigations I'm suggesting are meant to align with that guidance without breaking CCIP Read support.

• Default-on exposure. CCIP Read is enabled by default on all web3.py providers (global_ccip_read_enabled = True). Users who never intend to use CCIP Read, and who may not even know the feature exists, are silently exposed. A feature that makes unsanitized outbound requests to attacker-controlled URLs should not be enabled by default without safety guardrails.

• Library vs. application responsibility. web3.py is a widely-used library. Expecting every downstream application to independently implement SSRF protections around .call() is unreasonable, especially for a feature that fires automatically and invisibly on a specific revert pattern. Safe defaults at the library level are the standard expectation for any library that issues outbound HTTP requests to externally-controlled URLs.

Affected Code

Sync CCIP handler

File: web3/utils/exception_handling.py (lines 42-58)

Contract-controlled URLs are requested via requests with no destination validation:

session = requests.Session()
for url in offchain_lookup_payload["urls"]:
    formatted_url = URI(
        str(url)
        .replace("{sender}", str(formatted_sender))
        .replace("{data}", str(formatted_data))
    )

    try:
        if "{data}" in url and "{sender}" in url:
            response = session.get(formatted_url, timeout=DEFAULT_HTTP_TIMEOUT)
        else:
            response = session.post(
                formatted_url,
                json={"data": formatted_data, "sender": formatted_sender},
                timeout=DEFAULT_HTTP_TIMEOUT,
            )

(The request is issued before response validation; subsequent logic parses JSON and enforces a "data" field.)

Key observations:

• requests follows redirects by default (allow_redirects=True).
• No allow_redirects=False is set.
• No validation of formatted_url before the request.
• The placeholder check…