SSL_CTX_SET_MAX_CERT_LIST(3ossl)

💅 SSL_CTX_SET_MAX_CERT_LIST 💅

okay bestie so this is the OpenSSL manual page for SSL_CTX_SET_MAX_CERT_LIST, and it's literally all about how big a certificate chain your peer is allowed to send you before you're like "bestie no 💀". Buckle up, it's giving security engineering ✨

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✨ NAME ✨

SSL_CTX_set_max_cert_list, SSL_CTX_get_max_cert_list, SSL_set_max_cert_list, SSL_get_max_cert_list — manipulate the allowed size for the peer's certificate chain 🎀

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🌸 SYNOPSIS 🌸

#include <openssl/ssl.h>

long SSL_CTX_set_max_cert_list(SSL_CTX *ctx, long size);
long SSL_CTX_get_max_cert_list(SSL_CTX *ctx);

long SSL_set_max_cert_list(SSL *ssl, long size);
long SSL_get_max_cert_list(SSL *ctx);

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🦋 DESCRIPTION 🦋

SSL_CTX_set_max_cert_list() sets the maximum size allowed for the peer's certificate chain for all SSL objects created from ctx to be size bytes. The SSL objects inherit the setting that was valid for ctx at the time SSL_new(3) is being called. so like, timing matters, bestie ⏰

SSL_CTX_get_max_cert_list() returns the currently set maximum size for ctx.

SSL_set_max_cert_list() sets the maximum size allowed for the peer's certificate chain for ssl to be size bytes. This setting stays valid until a new value is set. it's not going anywhere unless you say so 💅

SSL_get_max_cert_list() returns the currently set maximum size for ssl.

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🔥 NOTES 🔥

During the handshake process, the peer may send a certificate chain. The TLS/SSL standard does not give any maximum size of the certificate chain. The OpenSSL library handles incoming data by a dynamically allocated buffer. In order to prevent this buffer from growing without bounds due to data received from a faulty or malicious peer, a maximum size for the certificate chain is set. so it's basically a lil guardrail against chaos 😤

The default value for the maximum certificate chain size is 100kB (30kB on the 16-bit DOS platform). This should be sufficient for usual certificate chains (OpenSSL's default maximum chain length is 10, see SSL_CTX_set_verify(3), and certificates without special extensions have a typical size of 1-2kB).

so yeah, the default is highkey generous. if your chain is bigger than that, something is giving unusual 🌈

For special applications it can be necessary to extend the maximum certificate chain size allowed to be sent by the peer, see e.g. the work on "Internet X.509 Public Key Infrastructure Proxy Certificate Profile" and "TLS Delegation Protocol" at http://www.ietf.org/ and http://www.globus.org/ .

Under normal conditions it should never be necessary to set a value smaller than the default, as the buffer is handled dynamically and only uses the memory actually required by the data sent by the peer. literally it only eats what it needs 🍓

⚠️ If the maximum certificate chain size allowed is exceeded, the handshake will fail with an SSL_R_EXCESSIVE_MESSAGE_SIZE error. no cap, that's the error you'll see 💀

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💖 RETURN VALUES 💖

SSL_CTX_set_max_cert_list() and SSL_set_max_cert_list() return the previously set value. (yes, the old one, so you can restore it later, main character energy 👑)

SSL_CTX_get_max_cert_list() and SSL_get_max_cert_list() return the currently set value.

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🎀 SEE ALSO 🎀

• ssl(7)
• SSL_new(3)
• SSL_CTX_set_verify(3)

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📜 COPYRIGHT 📜

Copyright 2001-2020 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <https://www.openssl.org/source/license.html>.

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okay that's the whole page bestie, you ate 🫶 this was OpenSSL 3.5.9, dated 2026-09-29, and yeah we did a little SSL_CTX_SET_MAX_CERT_LIST(3ossl) moment together. go forth and set sensible buffer limits, periodt 💜✨