What is CVE-2026-9546?

CVE-2026-9546 is a high-severity vulnerability in Curl, classified under CWE-200 EXPOSURE OF SENSITIVE INFORMATION TO AN UNAUTHORIZED ACTOR. CVSS score: 7.5/10. Published 2026-07-03.

How severe is CVE-2026-9546?

High severity. CVSS v3 base score is 7.5 out of 10.

Vulnerability in Curl

CVE-2026-9546

A vulnerability in libcurl caused the HTTP `Referer:` header to persist even when explicitly cleared. While the documentation states that passing NULL to `CURLOPT_REFERER` suppresses the header, the option failed to clear the internal state. As a result the previous referrer string was erroneously reused and sent in subsequent requests, potentially leaking sensitive information to unintended servers.

EPSS: 0.004 (32.6th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N.

Affected products

Curl — versions 8.20.0, 8.19.0, 8.18.0
Haxx Curl

References

2499f714-1537-4658-8207-48ae4bb9eae9 (Third Party Advisory)
2499f714-1537-4658-8207-48ae4bb9eae9 (Patch, Vendor Advisory)
2499f714-1537-4658-8207-48ae4bb9eae9 (Exploit, Third Party Advisory, Issue Tracking)

Frequently asked questions

What is CVE-2026-9546?: CVE-2026-9546 is a high-severity vulnerability in Curl, classified under CWE-200 EXPOSURE OF SENSITIVE INFORMATION TO AN UNAUTHORIZED ACTOR. CVSS score: 7.5/10. Published 2026-07-03.
How severe is CVE-2026-9546?: High severity. CVSS v3 base score is 7.5 out of 10.