CVE-2026-6276

stale custom cookie host causes cookie leak

HIGH
7.5
CVSS Score
Published: May 13, 2026 at 08:28 AM UTC
Updated: September 15, 2026 at 07:35 AM UTC
1 product affected across 1 vendorCurl

Using curl by curl?

Get instant alerts when new vulnerabilities affect curl - before attackers find them.

Real-time alertsTrack your software stackFree plan available
Severity
HIGH7.5
Exploit prediction
EPSS 0.3%
SSVC
PoC

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Vendor states this is fixed in 3a19987a87f393d9394fe5acc7643f6c263c92db (fixed)
Affected range stops below 8.14.2, so it looks safe — our inference, not a vendor statement
Affected range stops below 8.16.1, so it looks safe — our inference, not a vendor statement
Affected range stops below 8.20.0, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

Patch and advisory references

References (4)

PatchVendor Advisory
Source: cverecord
https://curl.se/docs/CVE-2026-6276.html
ExploitIssue TrackingThird Party Advisory
Source: cverecord
https://hackerone.com/reports/3671818
Mailing ListThird Party Advisory
Source: af854a3a-2127-422b-91ae-364da2661108
http://www.openwall.com/lists/oss-security/2026/04/29/13

SSVC — Action Prioritization

SSVCPoCAutomatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

7.5HIGHCISA-ADP
Attack Vector
NETWORK
Complexity
LOW
Privileges
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
NONE
Integrity
NONE
Availability
HIGH
Vector?

Quick Info

StatusMODIFIED
CWE
CWE-319CWE-346

Get alerted

Stop reading CVE feeds looking for your own stack

Track the products you run and VulnTracker tells you when a new CVE affects them — with what is known about fixing it, and nothing about the rest.

Free plan, no card