What is CVE-2026-11856?

CVE-2026-11856 is a critical-severity vulnerability in Curl, classified under Authentication Bypass by Capture-replay. CVSS score: 9.8/10. Published 2026-07-03.

How severe is CVE-2026-11856?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Vulnerability in Curl

CVE-2026-11856

Successfully using libcurl to do a transfer to a specific HTTP origin (`hostA`) with **Digest** authentication and then changing the origin to a different one (`hostB`) for a second transfer, reusing the same handle, makes libcurl wrongly pass on the `Authorization:` header field meant for `hostA`, to `hostB`.

EPSS: 0.006 (45.4th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

Affected products

Curl — versions 8.20.0, 8.19.0, 8.18.0
Haxx Curl

Weakness classification (CWE)

CWE-294 — Authentication Bypass by Capture-replay

References

2499f714-1537-4658-8207-48ae4bb9eae9 (Vendor 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-2026-11856?: CVE-2026-11856 is a critical-severity vulnerability in Curl, classified under Authentication Bypass by Capture-replay. CVSS score: 9.8/10. Published 2026-07-03.
How severe is CVE-2026-11856?: Critical severity. CVSS v3 base score is 9.8 out of 10.