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Fencer Vulns
medium 5.9

CVE-2026-6253 json

proxy credentials leak over redirect-to proxy

published 2026-05-13 5 mo ago modified 2026-09-15 55 d ago also EUVD-2026-29927 , JLSEC-2026-1206

cvss
5.9
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.7%
EPSS 0.7% chance of exploitation in 30 days, percentile 54%
public exploits
0
none known

Summary

curl might erroneously pass on credentials for a first proxy to a second proxy.

This can happen when the following conditions are true:

1. curl is setup to use specific different proxies for different URL schemes 2. the first proxy needs credentials 3. the second proxy uses no credentials 4. while using the first proxy (using say `http://`), curl is asked to follow a redirect to a URL using another scheme (say `https://`), accessed using a second, different, proxy

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-2026-6253

  • 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-2026-6253

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 RHEL 10.2 8.12.1-4.el10_2.7
  • libcurl RHEL 10.2 8.12.1-4.el10_2.7
  • libcurl-minimal RHEL 10.2 8.12.1-4.el10_2.7
  • 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-2026:80512RHSA-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 AlmaLinux 10 8.12.1-4.el10_2.7
  • libcurl AlmaLinux 10 8.12.1-4.el10_2.7
  • libcurl-minimal AlmaLinux 10 8.12.1-4.el10_2.7

almalinux advisories ALSA-2026:80512

  • curl Rocky Linux 10 8.12.1-4.el10_2.7

rocky linux advisories RLSA-2026:80512

  • 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-2026-6253

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 8.11.1-9
  • cmake Azure Linux 3.0 3.30.3-14

azure linux advisories AZL-86666AZL-86676

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-2026-6253 updated cvss 5.3

curl: curl: Proxy credential disclosure via redirects to unauthenticated proxies

  • 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 snphost Red Hat Enterprise Linux AI (RHEL AI) 3 rust
    affected: workaround, no fix available
  • 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 Cost Management On-Premise 1 costmanagement/costmanagement-ui-rhel10 1792605272
    fixed: vendor fix RHSA-2026:87400
  • Red Hat Enterprise Linux AppStream (v. 10) libcurl-devel 8.12.1-4.el10_2.7, curl-debuginfo 8.12.1-4.el10_2.7, curl-debugsource 8.12.1-4.el10_2.7, libcurl-debuginfo 8.12.1-4.el10_2.7, libcurl-minimal-debuginfo 8.12.1-4.el10_2.7 Red Hat Enterprise Linux BaseOS (v. 10) curl 8.12.1-4.el10_2.7, libcurl 8.12.1-4.el10_2.7, libcurl-minimal 8.12.1-4.el10_2.7
    fixed: vendor fix RHSA-2026:80512
  • 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 JBoss Core Services 2.4.62.SP5
    fixed: vendor fix RHSA-2026:56869
show 2 more
  • 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 SSVC

Exploitation
Proof of concept is public
Automatable
no
Technical impact
partial
Assessed
5 mo ago

Exploit prediction

0.72% chance of exploitation in the next 30 days, higher than 54% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • hackerone.com https://hackerone.com/reports/3669637 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CISA ADP 3.1 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
CNA 3.1 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
OSV 3.1 5.9 CVSS:3.1/AV:N/AC:H/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
<8.20.0+0
8.20.0+0

Affected products

  • curl curl

Classification

Weakness
  • CWE-522 Insufficiently Protected Credentials

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.