CVE-2026-9545

CVE-2026-9545 · exposing HTTP/3 early data

This page contains facts from public vulnerability sources. Check the original advisory before updating.

In this scenario, libcurl first uses a proper HTTP/3 server for the initial transfers, and when it makes a second transfer to the same site it has been replaced by the attacker's impostor machine - without a valid certificate. When libcurl returns to the hostname the second time with a cached SSL session (`CURLOPT_SSL_SESSIONID_CACHE` is not disabled) and early data enabled (the `CURLSSLOPT_EARLYDATA` bit is set in `CURLOPT_SSL_OPTIONS`), libcurl might send off the second request's bytes on that new connection *before* enforcing the certificate verification failure. Potentially leaking sensitive information.

CVSS 7.5 · High · EPSS 0.4% · Fix available

Published

2026-07-03T06:17:55.931Z

Updated

2026-09-15T06:03:31.804Z

Stack: system

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