CVE-2026-11856: curl — Exploit & Fix

Description

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`.

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CVSS v3.1 Score

9.8

CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS — Exploit Prediction

0.0060

Probability of exploitation

0.46%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-294 CWE-294

Affected Products

Vendor	Product	Versions
haxx	curl	7.10.6 — 8.21.0

References

Advisories & Patches

https://curl.se/docs/CVE-2026-11856.html https://curl.se/docs/CVE-2026-11856.json

Exploits

https://hackerone.com/reports/3793260 https://hackerone.com/reports/3793260

Frequently Asked Questions

What is 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`. It has a CVSS v3.1 base score of 9.8 (CRITICAL).

How severe is CVE-2026-11856? +

CVE-2026-11856 has a CVSS v3.1 score of 9.8 out of 10, rated CRITICAL. This is a critical vulnerability that should be patched immediately. The EPSS score is 0.0060, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-11856? +

CVE-2026-11856 affects products from haxx, specifically: curl. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-11856? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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