exposing HTTP/3 early data
CVE-2026-9545 is fixed in 13 products on 1 platform, first by curl 8.18.0-1ubuntu2.2, released June 26, 2026. It is not reported as exploited. Patch Radar priority: High.
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uses a proper HTTP/3 server for the initial transfers, and when it makes a second transfer to the same site it has been replaced by the attacker's impostor machine - without a valid certificate.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.
Where it's fixed
| Product | Fixed in | Fix | Released |
|---|---|---|---|
| Linux | |||
| curl · Debian 14 | 8.21.0~rc2-1 | DEBIAN-CVE-2026-9545 | Jul 24, 2026 |
| curl · Ubuntu 25.10 (questing) | 8.14.1-2ubuntu1.4 | curl 8.14.1-2ubuntu1.4 | Jul 3, 2026 |
| curl · Ubuntu 26.04.1 LTS (resolute) | 8.18.0-1ubuntu2.2 | curl 8.18.0-1ubuntu2.2 | Jun 26, 2026 |
| curl · amzn 2023 | 8.21.0-5.amzn2023.0.1 | ALAS2023-2026-2132 | Sep 14, 2026 |
| curl · opensuse-leap 16.0 | 8.14.1-160000.8.1 | OPENSUSE-SU-2026:21272-1 | Jul 8, 2026 |
| curl · sles 15.6 | 8.14.1-150600.4.46.1 | SUSE-SU-2026:2926-1 | Jul 13, 2026 |
| curl · sles 15.7 | 8.14.1-150700.7.20.1 | SUSE-SU-2026:2925-1 | Jul 13, 2026 |
| curl · sles 16.0 | 8.14.1-160000.8.1 | SUSE-SU-2026:22582-1 | Jul 8, 2026 |
| curl-debuginfo · amzn 2023 | 8.21.0-5.amzn2023.0.1 | ALAS2023-2026-2132 | Sep 14, 2026 |
| curl-debugsource · amzn 2023 | 8.21.0-5.amzn2023.0.1 | ALAS2023-2026-2132 | Sep 14, 2026 |
| curl-mini · sles 16.0 | 8.14.1-160000.8.1 | SUSE-SU-2026:22582-1 | Jul 8, 2026 |
| curl-minimal · amzn 2023 | 8.21.0-5.amzn2023.0.1 | ALAS2023-2026-2132 | Sep 14, 2026 |
| curl-minimal-debuginfo · amzn 2023 | 8.21.0-5.amzn2023.0.1 | ALAS2023-2026-2132 | Sep 14, 2026 |
| libcurl · amzn 2023 | 8.21.0-5.amzn2023.0.1 | ALAS2023-2026-2132 | Sep 14, 2026 |
| libcurl-debuginfo · amzn 2023 | 8.21.0-5.amzn2023.0.1 | ALAS2023-2026-2132 | Sep 14, 2026 |
| libcurl-devel · amzn 2023 | 8.21.0-5.amzn2023.0.1 | ALAS2023-2026-2132 | Sep 14, 2026 |
| libcurl-minimal · amzn 2023 | 8.21.0-5.amzn2023.0.1 | ALAS2023-2026-2132 | Sep 14, 2026 |
| libcurl-minimal-debuginfo · amzn 2023 | 8.21.0-5.amzn2023.0.1 | ALAS2023-2026-2132 | Sep 14, 2026 |
| libcurl3t64-gnutls · Ubuntu 25.10 (questing) | 8.14.1-2ubuntu1.4 | libcurl3t64-gnutls 8.14.1-2ubuntu1.4 | Jul 3, 2026 |
| libcurl3t64-gnutls · Ubuntu 26.04.1 LTS (resolute) | 8.18.0-1ubuntu2.2 | libcurl3t64-gnutls 8.18.0-1ubuntu2.2 | Jun 26, 2026 |
| libcurl4t64 · Ubuntu 25.10 (questing) | 8.14.1-2ubuntu1.4 | libcurl4t64 8.14.1-2ubuntu1.4 | Jul 3, 2026 |
| libcurl4t64 · Ubuntu 26.04.1 LTS (resolute) | 8.18.0-1ubuntu2.2 | libcurl4t64 8.18.0-1ubuntu2.2 | Jun 26, 2026 |
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