CVE-2026-9545

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.

High
CVSS
7.5
Important
Exploitation
None reported
No vendor assessment
CISA KEV
Not listed
Not in the Known Exploited Vulnerabilities catalog
EPSS
0.0041
35th percentile

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uses a proper HTTP/3 server for the initial transfers, and when it makes a second transfer to the same site it has been replaced by the attacker's impostor machine - without a valid certificate.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

ProductFixed inFixReleased
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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