CVE-2026-9545
Description
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uses a proper HTTP/3 server for the initial transfers, and when it makes a second transfer to the same site it has been replaced by the attacker's impostor machine - without a valid certificate.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.
How to fix
- haxx curl8.21.0 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| haxx curl | 8.11.0 ≤ v < 8.21.0 | 8.21.0 |
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