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Fencer Vulns
medium 6.5

CVE-2026-5545 json

wrong reuse of HTTP Negotiate connection

published 2026-05-13 5 mo ago modified 2026-09-15 55 d ago also EUVD-2026-29923 , GHSA-6g7g-56fm-f8mp , JLSEC-2026-1204

cvss
6.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.4%
EPSS 0.4% chance of exploitation in 30 days, percentile 35%
public exploits
0
none known

Summary

libcurl might in some circumstances reuse the wrong connection when asked to do an authenticated HTTP(S) request after a Negotiate-authenticated one, when both use the same host.

libcurl features a pool of recent connections so that subsequent requests can reuse an existing connection to avoid overhead.

When reusing a connection a range of criteria must be met. Due to a logical error in the code, a request that was issued by an application could wrongfully reuse an existing connection to the same server that was authenticated using different credentials.

An application that first uses Negotiate authentication to a server with `user1:password1` and then does another operation to the same server asking for any authentication method but for `user2:password2` (while the previous connection is still alive) - the second request gets confused and wrongly reuses the same connection and sends the new request over that connection thinking it uses a mix of user1's and user2's credentials when it is in fact still using the connection authenticated for user1...

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~rc2-1

debian advisories DEBIAN-CVE-2026-5545

  • 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
  • curl Ubuntu Pro 20.04 LTS 7.68.0-1ubuntu2.25+esm5

ubuntu advisories UBUNTU-CVE-2026-5545

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

alpine advisories ALPINE-CVE-2026-5545

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-86664AZL-86928

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-2026-5545 updated cvss 6.5

curl: libcurl: Authentication bypass due to incorrect HTTP Negotiate connection reuse

  • 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
    affected: workaround, no fix available
  • Red Hat Enterprise Linux AI (RHEL AI) 3 rust 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
none
Automatable
no
Technical impact
partial
Assessed
5 mo ago

Exploit prediction

0.41% chance of exploitation in the next 30 days, higher than 35% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • hackerone.com https://hackerone.com/reports/3642555 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CISA ADP 3.1 6.5 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:N
NVD 3.1 6.5 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:N
CNA 3.1 6.5 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:N
OSV 3.1 6.5 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:N

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-305 Authentication Bypass by Primary Weakness
  • CWE-613 DEPRECATED: Insufficient Session Expiration

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.