CVE-2026-9545

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uses a proper HTTP/3 server for the initial transfers, and when it makes a second transfer to the same site it has been replaced by the attacker's impostor machine - without a valid certificate.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.

• https://curl.se/docs/CVE-2026-9545.htmlPatch, Vendor Advisory
• https://curl.se/docs/CVE-2026-9545.jsonVendor Advisory
• https://hackerone.com/reports/3752888Exploit, Issue Tracking, Third Party Advisory
• https://hackerone.com/reports/3752888Exploit, Issue Tracking, Third Party Advisory

Published

Jul 3, 2026

Last Modified

Jul 7, 2026

Status

Analyzed

• How Strix found a critical auth bypass in etcdStrix autonomously discovered a critical authentication bypass in etcd, later designated CVE-2026-33413.
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