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CVE-2026-6276: Haxx Curl Security Vulnerability (CVSS 7.5)

CVE-2026-6276 is a high severity security vulnerability in Haxx Curl with a CVSS score of 7.5. Apply the vendor fix and confirm exposure on internet facing and business critical assets first.

Last updated: Sep 15, 2026

Quick answer

Direct answer

CVE-2026-6276 is a high severity security vulnerability in Haxx Curl with a CVSS score of 7.5. Apply the vendor fix and confirm exposure on internet facing and business critical assets first.

Risk scores

CVSS base score
7.5HIGH
EPSS probability
0.35%
Higher than 27 percent of all CVEs
CISA KEV
Not listed
CVSS metricWhat it means
Attack vector (AV:N)Network: reachable remotely
Attack complexity (AC:L)Low complexity
Privileges required (PR:N)No privileges required
User interaction (UI:N)No user interaction
Scope (S:U)Scope unchanged
Confidentiality (C:N)No confidentiality impact
Integrity (I:N)No integrity impact
Availability (A:H)High availability impact

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

About Haxx Curl

CVE-2026-6276 affects Haxx Curl, a product from Haxx. Before acting, confirm where Haxx Curl runs in your estate, who owns it and whether it is reachable from the internet, because exposure decides real risk more than the score alone.

What the flaw is

In plain terms: 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.

Based on its CVSS vector, the flaw can be reached over the network, needs no login, and needs no user interaction. Apply the vendor fix and confirm exposure on internet facing and business critical assets first.

Affected versions and timeline

FieldDetail
ProductHaxx Curl
Affected versionsCurl from 7.71.0 before 8.20.0
PublishedMay 13, 2026
Last modifiedSep 15, 2026
Added to CISA KEVNot listed
Assigning CNA2499f714-1537-4658-8207-48ae4bb9eae9

How to detect it

  • Inventory every instance of Haxx Curl and record the running version against the affected range above.
  • Check external attack surface scans for internet facing instances of the component.
  • Review logs on affected systems for unusual requests, errors or new processes around the vulnerable function.
  • Confirm with an authenticated vulnerability scan once your scanner has a check for this CVE.

How to fix it

  • Apply the fixed version of Haxx Curl named in the vendor advisory.
  • If patching must wait, restrict network access to the affected service and put it behind authentication or a web application firewall rule.
  • Rescan after the change to prove the exposure is gone, then close the ticket.

CTEM action plan

CTEM stageWhat to do for this CVE
ScopeAdd every business service that depends on Haxx Curl to the current CTEM cycle.
DiscoverFind all instances, including shadow and cloud deployments, and record versions and exposure.
PrioritizeRank using EPSS and CVSS together with asset exposure and business impact.
ValidateConfirm the flaw is reachable and exploitable in your environment and that compensating controls work.
MobilizeAssign the fix to the asset owner with a due date matched to the priority, then verify closure.

CWE References

Technical References

Frequently asked questions

CVE-2026-6276 is a high severity security vulnerability in Haxx Curl with a CVSS score of 7.5. Apply the vendor fix and confirm exposure on internet facing and business critical assets first.

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