CVE-2026-9545
exposing HTTP/3 early data
- State
- Published
- Severity
- 7.5 High
- Published
- Jul 3, 2026
- Updated
- Sep 15, 2026
- Reserved
- May 26, 2026
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uses a proper HTTP/3 server for the initial transfers, and when it makes a second transfer to the same site it has been replaced by the attacker's impostor machine - without a valid certificate.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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 3.1 | 7.5 High | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N | CISA-ADP |
Weaknesses
- CWE-200 Exposure of Sensitive Information to an Unauthorized Actor
Affected Products
| Product | Versions |
|---|---|
curlcurl |
|
curlcurl |
|
curlcurl |
|
References
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