CVE-2026-6276: curl — Exploit & Fix

Description

Using libcurl, when a custom `Host:` header is first set for an HTTP request and a second request is subsequently done using the same *easy handle* but without the custom `Host:` header set, the second request would use stale information and pass on cookies meant for the first host in the second request. Leak them.

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CVSS v3.1 Score

7.5

HIGH

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

EPSS — Exploit Prediction

0.0001

Probability of exploitation

0.02%

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-319 CWE-319

Affected Products

Vendor	Product	Versions
haxx	curl	7.71.0 — 8.20.0

References

Advisories & Patches

https://curl.se/docs/CVE-2026-6276.html

Exploits

https://hackerone.com/reports/3671818 https://hackerone.com/reports/3671818

Other References

https://curl.se/docs/CVE-2026-6276.json http://www.openwall.com/lists/oss-security/2026/04/29/13

Frequently Asked Questions

What is CVE-2026-6276? +

Using libcurl, when a custom `Host:` header is first set for an HTTP request and a second request is subsequently done using the same *easy handle* but without the custom `Host:` header set, the second request would use stale information and pass on cookies meant for the first host in the second request. Leak them. It has a CVSS v3.1 base score of 7.5 (HIGH).

How severe is CVE-2026-6276? +

CVE-2026-6276 has a CVSS v3.1 score of 7.5 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching. The EPSS score is 0.0001, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-6276? +

CVE-2026-6276 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-2026-6276? +

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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