CVE-2026-9545
exposing HTTP/3 early data
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uses a proper HTTP/3 server for the initial transfers, and when it makes a second transfer to the same site it has been replaced by the attacker's impostor machine - without a valid certificate.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.
INFO
Published Date :
July 3, 2026, 7:16 a.m.
Last Modified :
July 7, 2026, 3:03 p.m.
Remotely Exploit :
Yes !
Source :
2499f714-1537-4658-8207-48ae4bb9eae9
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | HIGH | 134c704f-9b21-4f2e-91b3-4a467353bcc0 |
Solution
- Disable the CURLSSLOPT_EARLYDATA option.
- Ensure certificate verification is not bypassed.
- Review SSL session caching configurations.
- Keep libcurl updated to the latest version.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-9545.
| URL | Resource |
|---|---|
| https://curl.se/docs/CVE-2026-9545.html | Patch Vendor Advisory |
| https://curl.se/docs/CVE-2026-9545.json | Vendor Advisory |
| https://hackerone.com/reports/3752888 | Exploit Issue Tracking Third Party Advisory |
| https://hackerone.com/reports/3752888 | Exploit Issue Tracking Third Party Advisory |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-9545 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-9545
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-9545 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-9545 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
Initial Analysis by [email protected]
Jul. 07, 2026
Action Type Old Value New Value Added CWE NVD-CWE-noinfo Added CPE Configuration OR *cpe:2.3:a:haxx:curl:*:*:*:*:*:*:*:* versions from (including) 8.11.0 up to (excluding) 8.21.0 Added Reference Type curl: https://curl.se/docs/CVE-2026-9545.html Types: Patch, Vendor Advisory Added Reference Type curl: https://curl.se/docs/CVE-2026-9545.json Types: Vendor Advisory Added Reference Type curl: https://hackerone.com/reports/3752888 Types: Exploit, Issue Tracking, Third Party Advisory Added Reference Type CISA-ADP: https://hackerone.com/reports/3752888 Types: Exploit, Issue Tracking, Third Party Advisory -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Jul. 06, 2026
Action Type Old Value New Value Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N Added Reference https://hackerone.com/reports/3752888 Added SSVC {'id': 'CVE-2026-9545', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'poc'}, {'automatable': 'yes'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-07-06T16:52:42.898546Z'} -
New CVE Received by 2499f714-1537-4658-8207-48ae4bb9eae9
Jul. 03, 2026
Action Type Old Value New Value Added Affected [{'vendor': 'curl', 'product': 'curl', 'versions': [{'status': 'affected', 'version': '8.20.0', 'versionType': 'semver', 'lessThanOrEqual': '8.20.0'}, {'status': 'affected', 'version': '8.19.0', 'versionType': 'semver', 'lessThanOrEqual': '8.19.0'}, {'status': 'affected', 'version': '8.18.0', 'versionType': 'semver', 'lessThanOrEqual': '8.18.0'}, {'status': 'affected', 'version': '8.17.0', 'versionType': 'semver', 'lessThanOrEqual': '8.17.0'}, {'status': 'affected', 'version': '8.16.0', 'versionType': 'semver', 'lessThanOrEqual': '8.16.0'}, {'status': 'affected', 'version': '8.15.0', 'versionType': 'semver', 'lessThanOrEqual': '8.15.0'}, {'status': 'affected', 'version': '8.14.1', 'versionType': 'semver', 'lessThanOrEqual': '8.14.1'}, {'status': 'affected', 'version': '8.14.0', 'versionType': 'semver', 'lessThanOrEqual': '8.14.0'}, {'status': 'affected', 'version': '8.13.0', 'versionType': 'semver', 'lessThanOrEqual': '8.13.0'}, {'status': 'affected', 'version': '8.12.1', 'versionType': 'semver', 'lessThanOrEqual': '8.12.1'}, {'status': 'affected', 'version': '8.12.0', 'versionType': 'semver', 'lessThanOrEqual': '8.12.0'}, {'status': 'affected', 'version': '8.11.1', 'versionType': 'semver', 'lessThanOrEqual': '8.11.1'}, {'status': 'affected', 'version': '8.11.0', 'versionType': 'semver', 'lessThanOrEqual': '8.11.0'}], 'defaultStatus': 'unaffected'}] Added 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. Added Reference https://curl.se/docs/CVE-2026-9545.html Added Reference https://curl.se/docs/CVE-2026-9545.json Added Reference https://hackerone.com/reports/3752888