Vulnerability · Published Jul 3, 2026 · Assigned by curl
CVE-2026-9545exposing HTTP/3 early data
High 7.5
In plain English
A high-severity information exposure in curl from curl. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 35% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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uses a proper HTTP/3 server for the initial transfers, and when it makes a second transfer to the same site it has been replaced by the attacker's impostor machine - without a valid certificate.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 packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine:v3.23 | curl | 8.22.0-r0 | ALPINE-CVE-2026-9545 |
| Alpine:v3.24 | curl | 8.21.0-r0 | ALPINE-CVE-2026-9545 |
| Debian:13 | curl | no fix listed | DEBIAN-CVE-2026-9545 |
| Debian:14 | curl | 8.21.0~rc2-1 | DEBIAN-CVE-2026-9545 |
| Ubuntu:25.10 | curl | 8.14.1-2ubuntu1.4 | UBUNTU-CVE-2026-9545 |
| Ubuntu:26.04:LTS | curl | 8.18.0-1ubuntu2.2 | UBUNTU-CVE-2026-9545 |
Affected products (as reported)
Weakness: CWE-200 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N