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uses a proper HTTP/3 server for the initial transfers, and when it makes a second transfer to the same site it has been replaced by the attacker's impostor machine - without a valid certificate.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 Details
- CVSS 3.1 Base Score: 7.5
- CVSS 3.1 Vector: (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N)
Covered by Rapid7
| Product | Vendor Advisory | Solution File | Added | Published |
|---|---|---|---|---|
| Alpine Linux | — | Upgrade curl | Jul 6, 2026 | Jul 3, 2026 |
| Amazon_linux_2023 | — | Upgrade libcurl-minimal-debuginfoUpgrade libcurlUpgrade curl-minimalUpgrade curlUpgrade libcurl-develUpgrade curl-debuginfoUpgrade curl-debugsourceUpgrade libcurl-minimalUpgrade libcurl-debuginfoUpgrade curl-minimal-debuginfo | Sep 30, 2026 | Jul 3, 2026 |
| Ubuntu | — | Upgrade libcurl3-nss (Ubuntu Pro)Upgrade libcurl3-nssUpgrade libcurl4-openssl-dev (Ubuntu Pro)Upgrade libcurl3t64-gnutlsUpgrade curlUpgrade curl (Ubuntu Pro)Upgrade libcurl4-nss-devUpgrade libcurl4-openssl-devUpgrade libcurl4-gnutls-dev (Ubuntu Pro)Upgrade libcurl4-gnutls-devUpgrade libcurl3-gnutls (Ubuntu Pro)Upgrade libcurl4-nss-dev (Ubuntu Pro)Upgrade libcurl4t64Upgrade libcurl4Upgrade libcurl3 (Ubuntu Pro)Upgrade libcurl3-gnutlsUpgrade libcurl4 (Ubuntu Pro) | Jul 1, 2026 | Jun 30, 2026 |
| Vmware Photon_os | — | Use 'tdnf update' to upgrade all packages to the latest version. | Aug 10, 2026 | Jul 3, 2026 |
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