What is CVE-2026-8927?

CVE-2026-8927 is a critical-severity vulnerability in Curl, classified under Authentication Bypass by Capture-replay. CVSS score: 9.1/10. Published 2026-07-03.

How severe is CVE-2026-8927?

Critical severity. CVSS v3 base score is 9.1 out of 10.

Vulnerability in Curl

CVE-2026-8927

When reusing a libcurl handle for sequential transfers driven by environment-variable proxy configuration, libcurl fails to clear the proxy authentication state between requests. Specifically, if the initial transfer authenticates against `proxyA` using Digest auth, a subsequent transfer routed through `proxyB` erroneously leaks the `Proxy-Authorization:` header intended solely for `proxyA`.

EPSS: 0.004 (36.0th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 9.1 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N.

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-2026-8927?: CVE-2026-8927 is a critical-severity vulnerability in Curl, classified under Authentication Bypass by Capture-replay. CVSS score: 9.1/10. Published 2026-07-03.
How severe is CVE-2026-8927?: Critical severity. CVSS v3 base score is 9.1 out of 10.