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Fencer Vulns
high 7.5

CVE-2026-6276 json

stale custom cookie host causes cookie leak

published 2026-05-13 5 mo ago modified 2026-09-15 55 d ago also EUVD-2026-29928 , GHSA-2jc6-hc33-hv48 , JLSEC-2026-1207

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 22%
public exploits
0
none known

Summary

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.

Patch / fix

  • julia CURL_jll 8.20.0+0
  • julia LibCURL_jll 8.20.0+0
  • curl curl 8.14.2, 8.16.1, 8.20.0
  • curl Debian 13 8.14.1-2+deb13u4
  • curl Debian 14 8.20.0~rc3-1

debian advisories DEBIAN-CVE-2026-6276

  • curl Ubuntu 22.04 LTS 7.81.0-1ubuntu1.24
  • curl Ubuntu 24.04 LTS 8.5.0-2ubuntu10.9
  • curl Ubuntu 25.10 8.14.1-2ubuntu1.3
  • curl Ubuntu 26.04 LTS 8.18.0-1ubuntu2.1

ubuntu advisories UBUNTU-CVE-2026-6276

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • curl hummingbird 1 8.20.0-0.1.hum1
  • libcurl hummingbird 1 8.20.0-0.1.hum1
  • libcurl-minimal hummingbird 1 8.20.0-0.1.hum1

red hat advisories RHSA-2026:12916

  • curl SLE Module for Basesystem 15 SP7 8.14.1-150700.7.23.1
  • curl SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 8.14.1-160000.6.1
  • curl-mini SLES for SAP applications 16.0, SLES 16.0 8.14.1-160000.6.1
  • curl SLES LTSS Extended Security 12 SP5 8.0.1-11.123.1

suse advisories SUSE-SU-2026:3798-1SUSE-SU-2026:2703-1SUSE-SU-2026:22146-1SUSE-SU-2026:22156-1

  • curl openSUSE Leap 16.0 8.14.1-160000.6.1
  • curl openSUSE Tumbleweed 8.20.0-1.1

opensuse advisories openSUSE-SU-2026:20973-1openSUSE-SU-2026:10674-1

  • curl Alpine 3.21 8.14.1-r3
  • curl Alpine 3.22 8.14.1-r4
  • curl Alpine 3.24, Alpine 3.23 8.20.0-r0

alpine advisories ALPINE-CVE-2026-6276

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • curl Azure Linux 3.0 8.11.1-7
  • cmake Azure Linux 3.0 3.30.3-14

azure linux advisories AZL-86655AZL-86679

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-6276 updated cvss 3.7

curl: libcurl: Information disclosure due to cookie leak when reusing connections with custom Host headers

  • Red Hat Confidential Compute Attestation build-of-trustee/trustee-rhel9, openshift-sandboxed-containers/osc-rhel9-operator, openshift-sandboxed-containers/osc-operator-bundle, openshift-sandboxed-containers/osc-podvm-builder-rhel9, openshift-sandboxed-containers/osc-podvm-payload-rhel9, confidential-compute-attestation-tech-preview/trustee-rhel9 Red Hat Logging Subsystem for Red Hat OpenShift openshift-logging/vector-rhel9, openshift-logging/fluentd-rhel9, openshift-logging/eventrouter-rhel9, openshift-logging/logging-view-plugin-rhel9, openshift-logging/cluster-logging-rhel9-operator, openshift-logging/log-file-metric-exporter-rhel9, +1 more Red Hat Enterprise Linux 6 curl, libcurl Red Hat Enterprise Linux 7 curl, libcurl Red Hat Enterprise Linux 8 curl, libcurl, libcurl-minimal
    affected: workaround, no fix available “Fix deferred”
  • Red Hat Enterprise Linux 9 curl, libcurl, snphost, curl-minimal, libcurl-minimal Red Hat Enterprise Linux 10 curl, snphost
    affected: workaround, no fix available
  • Red Hat Enterprise Linux AI (RHEL AI) 3 rust Red Hat JBoss Core Services curl Red Hat OpenShift Container Platform 4 openshift/ose-rhel-coreos-8, openshift/ose-rhel-coreos-9 Red Hat OpenShift Dev Spaces devspaces/code-rhel9 Red Hat Trusted Profile Analyzer rhtpa/rhtpa-trustification-service-rhel9
    affected: workaround, no fix available “Fix deferred”
  • Red Hat OpenShift AI (RHOAI) rhoai/odh-core-bff-rhel9, rhoai/odh-dashboard-rhel9, rhoai/odh-mod-arch-maas-rhel9, rhoai/odh-mod-arch-automl-rhel9, rhoai/odh-mod-arch-gen-ai-rhel9, rhoai/odh-mod-arch-mlflow-rhel9, +6 more
    under investigation
  • Red Hat Hardened Images curl 8.20.0-0.1.hum1, libcurl 8.20.0-0.1.hum1, libcurl-minimal 8.20.0-0.1.hum1
    fixed: vendor fix RHSA-2026:12916
  • Red Hat Enterprise Linux 9 rust, cargo, clippy, rustfmt, rust-gdb, rust-src, +9 more Red Hat Enterprise Linux 10 rust, trustee, s390utils, trustee-guest-components
    not affected: component not present
  • Red Hat Hardened Images rust Red Hat OpenShift AI (RHOAI) rhoai/odh-mlflow-rhel9, rhoai/odh-kube-rbac-proxy-rhel9, rhoai/odh-maas-controller-rhel9, rhoai/odh-mlflow-operator-rhel9, rhoai/odh-model-controller-rhel9, rhoai/odh-ogx-k8s-operator-rhel9, +14 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

cisa ICSA-26-293-05 updated cvss 7.5

Hitachi Energy RTU500 Product

  • Hitachi Energy RTU500 series CMU Firmware vers:RTU500_series_CMU_Firmware/>=13.5.1, <=13.5.4, vers:RTU500_series_CMU_Firmware/>=13.6.1, <=13.6.3, vers:RTU500_series_CMU_Firmware/>=13.7.1, <=13.7.8, vers:RTU500_series_CMU_Firmware/>=13.8.1, <=13.8.2
    affected: vendor fix, mitigation

Facts from CISA's republication of the vendor's own advisory (CSAF); the linked advisory is the authoritative source. CISA notification · csaf

CISA SSVC

Exploitation
Proof of concept is public
Automatable
yes
Technical impact
partial
Assessed
5 mo ago

Exploit prediction

0.29% chance of exploitation in the next 30 days, higher than 22% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • hackerone.com https://hackerone.com/reports/3671818 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CISA ADP 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
OSV 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
julia CURL_jll
<8.20.0+0
8.20.0+0
julia LibCURL_jll
>=7.71.1+0, <8.20.0+0
8.20.0+0

Affected products

  • curl curl

Classification

Weakness
  • CWE-346 Origin Validation Error
  • CWE-319 Cleartext Transmission of Sensitive Information

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.