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JLSEC-2026-1220 High 7.5

In this scenario, libcurl first uses a proper HTTP/3 server for the initial transfers, and when...

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JLSEC Published
Modified
Severity
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Affected Packages
CURL_jll >= 8.11.0+0, < 8.21.0+0
LibCURL_jll >= 8.11.0+0, < 8.21.0+0
Upstream
CVE-2026-9545 GHSA-6v72-wfcj-jv53 EUVD-2026-41493

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uses a proper HTTP/3 server for the initial transfers, and when it makes a second transfer to the same site it has been replaced by the attacker's impostor machine - without a valid certificate.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

References