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transfers, and when it makes a second transfer to the same site it has been
replaced by the attacker's impostor machine - without a valid certificate.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.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| curl | curl | 8.11.0 – < 8.14.2, 8.15.0 – < 8.16.1, 8.17.0 – < 8.20.1, 8.20.0, 8.19.0, 8.18.0, 8.17.0, 8.16.0, 8.15.0, 8.14.1, 8.14.0, 8.13.0, 8.12.1, 8.12.0, 8.11.1, 8.11.0 | 8.14.2 |
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | curl | 8.21.0~rc2-1 | — |
| Debian 13 | curl | No fix yet | — |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 26.04 LTS | curl | 8.18.0-1ubuntu2.2 | — |
| Ubuntu 25.10 | curl | 8.14.1-2ubuntu1.4 | — |
Red Hat
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Red Hat Hardened Images 1 | curl +3 | 8.21.0-0.1.1.hum1 | RHSA-2026:41240 |
SUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES 15 SP7 | curl | 8.14.1-150700.7.20.1 | SUSE-SU-2026:2925-1 |
| SLES 15 SP6 | curl | 8.14.1-150600.4.46.1 | SUSE-SU-2026:2926-1 |
| SLES 15 SP5 | curl | 8.14.1-150400.5.86.1 | SUSE-SU-2026:3043-1 |
| SLES 15 SP4 | curl | 8.14.1-150400.5.86.1 | SUSE-SU-2026:3043-1 |
Show 13 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES for SAP 16.0 | curl +1 | 8.14.1-160000.8.1 | SUSE-SU-2026:22582-1 |
| SLES for SAP 15 SP6 | curl | 8.14.1-150600.4.46.1 | SUSE-SU-2026:2926-1 |
| SLES 16.0 | curl +1 | 8.14.1-160000.8.1 | SUSE-SU-2026:22582-1 |
| SLE Micro 6.2 | curl | 8.14.1-160000.8.1 | SUSE-SU-2026:22553-1 |
| SLE Micro 6.1 | curl | 8.14.1-slfo.1.1_8.1 | SUSE-SU-2026:22889-1 |
| SLE Micro 6.0 | curl | 8.14.1-7.1 | SUSE-SU-2026:22709-1 |
| SLE Micro 5.5 | curl | 8.14.1-150400.5.86.1 | SUSE-SU-2026:3043-1 |
| SLE Micro 5.4 | curl | 8.14.1-150400.5.86.1 | SUSE-SU-2026:3043-1 |
| SLE Micro 5.3 | curl | 8.14.1-150400.5.86.1 | SUSE-SU-2026:3043-1 |
| SLE HPC 15 SP5 | curl | 8.14.1-150400.5.86.1 | SUSE-SU-2026:3043-1 |
| SLE HPC 15 SP4 | curl | 8.14.1-150400.5.86.1 | SUSE-SU-2026:3043-1 |
| SUSE Linux Enterprise Installer Updates 15 SP5 | curl | 8.14.1-150400.5.86.1 | SUSE-SU-2026:3043-1 |
| SUSE Linux Enterprise Installer Updates 15 SP4 | curl | 8.14.1-150400.5.86.1 | SUSE-SU-2026:3043-1 |
openSUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| openSUSE Tumbleweed | curl | 8.21.0-1.1 | openSUSE-SU-2026:11230-1 |
| openSUSE Leap 16.0 | curl | 8.14.1-160000.8.1 | openSUSE-SU-2026:21272-1 |
Alpine
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.24 | curl | 8.21.0-r0 | — |
| Alpine v3.23 | curl | 8.22.0-r0 | — |
Amazon Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Amazon Linux 2023 | curl +4 | 8.21.0-5.amzn2023.0.1 | ALAS2023-2026-2132 |
Advisories 12
- WID-SEC-2026-2052 cURL: Mehrere Schwachstellen BSI CERT-Bund (WID) · Nov 12, 2026
- RHSA-2026:41240 Red Hat Security Advisory: Red Hat Hardened Images RPMs Security Update Red Hat Security Advisories (RHSA) · Oct 20, 2026
- ALAS2023-2026-2132 Moderate: curl security update (Amazon Linux 2023) Amazon Linux Security Center (ALAS) · Sep 14, 2026
- SUSE-SU-2026:22889-1 Security update for curl SUSE / openSUSE Security Updates · Jul 28, 2026
- SUSE-SU-2026:22709-1 Security update for curl SUSE / openSUSE Security Updates · Jul 23, 2026
- SUSE-SU-2026:3043-1 Security update for curl SUSE / openSUSE Security Updates · Jul 16, 2026
- SUSE-SU-2026:22582-1 Security update for curl SUSE / openSUSE Security Updates · Jul 15, 2026
- SUSE-SU-2026:2926-1 Security update for curl SUSE / openSUSE Security Updates · Jul 15, 2026
- SUSE-SU-2026:2925-1 Security update for curl SUSE / openSUSE Security Updates · Jul 15, 2026
- SUSE-SU-2026:22553-1 Security update for curl SUSE / openSUSE Security Updates · Jul 14, 2026
- openSUSE-SU-2026:21272-1 Security update for curl SUSE / openSUSE Security Updates · Jul 11, 2026
- openSUSE-SU-2026:11230-1 curl-8.21.0-1.1 on GA media SUSE / openSUSE Security Updates · Jul 10, 2026