CVE-2026-9545

What it is

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uses a proper HTTP/3 server for the initial transfers, and when it makes a second transfer to the same site it has been replaced by the attacker's impostor machine - without a valid certificate.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

At a glance

Exploitability

Can be exploited over the network without logging in. High risk of data exposure.

Exploit odds

0.4% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2026-07-03 07:16 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-09-15 07:16 UTC Last updatedMost recent change to the record

Details

Published

2026-07-03 07:16 UTC

Last modified

2026-09-15 07:16 UTC

Exploit probability

0.4% · EPSS, next 30 days

Weakness

CWE-200 · Information exposure

Record status

Modified

Affected

• Haxx Curl < 8.21.0

Attack profile CVSS 3.1 · 7.5

Attack vector

Network

Complexity

Low

Privileges needed

None

User interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

None

Availability

None