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Fencer Vulns
high 7.5

CVE-2026-18798 json

QUIC Server May Trigger Double Free When Processing INITIAL Packet

published 2026-08-25 2 mo ago modified 2026-09-23 46 d ago also EUVD-2026-65480

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
1.7%
EPSS 1.7% chance of exploitation in 30 days, percentile 77%
public exploits
0
none known

Summary

Issue summary: QUIC server may double free QRX (QUIC record layer RX) object when channel creation fails for initial packet.

Impact summary: Double free leads to heap corruption, which typically results in termination of QUIC server process, leading to Denial of Service. There is so far no evidence that this double free is exploitable for remote code execution, thus it is considered highly improbable.

CWE: CWE-415: Double Free

Description: In order to validate initial packet, OpenSSL QUIC stack default packet handler (port_default_packet_handler()) creates a so-called QRX object. If the initial packet validates successfully with QRX object, the default packet handler proceeds to channel (connection object) creation. The QRX object used for packet validation is passed to port_bind_channel(), so it becomes part of the newly created connection. If port_bind_channel() fails, then it also frees the QRX object. Once port_bind_channel() returns, the port_default_packet_handler() detects the failure and proceeds to the error branch, where the same QRX object is freed for the second time.

The failure in port_bind_channel() function can be induced with a relatively low effort by a malformed (non RFC 9000 compliant) INITIAL packet. If the packet carries DCID (destination connection ID) which is shorter than 8 bytes, then port_bind_channel() jumps to the error path after ossl_quic_lcidm_enrol_odcid() detects that the DCID has invalid length.

FIPS impact: no The FIPS module is not affected, as the QUIC implementation is outside of the OpenSSL FIPS module boundary.

Patch / fix

  • OpenSSL OpenSSL 3.5.8, 3.6.4, 4.0.2
  • openssl Debian 13 3.5.7-1~deb13u2
  • openssl Debian 14 3.6.4-1

debian advisories DEBIAN-CVE-2026-18798

  • openssl Ubuntu 26.04 LTS 3.5.5-1ubuntu3.4

ubuntu advisories UBUNTU-CVE-2026-18798

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

  • openssl RHEL 9 1:3.5.8-1.el9_8
  • openssl-libs RHEL 9 1:3.5.8-1.el9_8
  • openssl-perl RHEL 9 1:3.5.8-1.el9_8
  • openssl RHEL 10.2 1:3.5.8-1.el10_2
  • openssl-libs RHEL 10.2 1:3.5.8-1.el10_2
  • openssl-perl RHEL 10.2 1:3.5.8-1.el10_2
  • openssl3 hummingbird 1 3.5.8-0.1.hum1
  • openssl3-libs hummingbird 1 3.5.8-0.1.hum1

red hat advisories RHSA-2026:67165RHSA-2026:67154RHSA-2026:59635RHSA-2026:59641

  • openssl-3 SLE Module for Basesystem 15 SP7 3.5.0-150700.5.50.1
  • openssl-3 SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 3.5.0-160000.10.1

suse advisories SUSE-SU-2026:4039-1SUSE-SU-2026:23463-1SUSE-SU-2026:23609-1

  • openssl-3 openSUSE Leap 16.0 3.5.0-160000.10.1
  • openssl-3 openSUSE Tumbleweed 3.5.3-8.1

opensuse advisories openSUSE-SU-2026:21744-1openSUSE-SU-2026:11623-1

  • openssl AlmaLinux 10 1:3.5.8-1.el10_2.alma.1
  • openssl-libs AlmaLinux 10 1:3.5.8-1.el10_2.alma.1
  • openssl-perl AlmaLinux 10 1:3.5.8-1.el10_2.alma.1
  • openssl AlmaLinux 9 1:3.5.8-1.el9_8
  • openssl-libs AlmaLinux 9 1:3.5.8-1.el9_8
  • openssl-perl AlmaLinux 9 1:3.5.8-1.el9_8

almalinux advisories ALSA-2026:67154ALSA-2026:67165

  • openssl Rocky Linux 9 1:3.5.8-1.el9_8
  • openssl Rocky Linux 10 1:3.5.8-1.el10_2

rocky linux advisories RLSA-2026:67165RLSA-2026:67154

  • openssl Alpine 3.24, Alpine 3.23, Alpine 3.22 3.5.8-r0

alpine advisories ALPINE-CVE-2026-18798

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

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-2026-18798 updated cvss 7.5

openssl: QUIC server may trigger double free when processing INITIAL packet

  • Red Hat JBoss Core Services jbcs-httpd24-openssl, jbcs-httpd24-openssl-libs, jbcs-httpd24-openssl-perl, jbcs-openssl-win6-x86_64.zip 3.5.5-SP4 Red Hat JBoss Web Server 6 jws-optional-native-components-win6-x86_64.zip 6.2.4.ER1 Red Hat JBoss Web Server 7 jws-optional-native-components-win6-x86_64.zip 6.2.4.ER1
    affected: workaround, no fix planned “Will not fix”
  • Red Hat OpenShift Container Platform 5 openshift/ose-rhel-coreos-9
    affected: workaround, no fix available
  • Red Hat Cert Manager support for Red Hat OpenShift release 1.20 cert-manager/cert-manager-operator-rhel9 1790272426, cert-manager/cert-manager-operator-rhel9 1790589855, cert-manager/jetstack-cert-manager-rhel9 1790223279, cert-manager/jetstack-cert-manager-rhel9 1790589912, cert-manager/cert-manager-istio-csr-rhel9 1790223719, cert-manager/cert-manager-istio-csr-rhel9 1790589914, +1 more
    fixed: vendor fix RHSA-2026:72475
  • Red Hat Cost Management 4 costmanagement/costmanagement-metrics-rhel9-operator 1790844333
    fixed: vendor fix RHSA-2026:81201
  • Red Hat Cost Management On-Premise 1 costmanagement/costmanagement-ui-rhel10 1791460851
    fixed: vendor fix RHSA-2026:79357
  • Red Hat Developer Hub 1.10 rhdh/rhdh-hub-rhel9 1791311495
    fixed: vendor fix RHSA-2026:79088
  • Red Hat Enterprise Linux AppStream (v. 9) openssl-perl 3.5.8-1.el9_8
    fixed: vendor fix RHSA-2026:67165
  • Red Hat Enterprise Linux AppStream (v. 10) openssl-perl 3.5.8-1.el10_2
    fixed: vendor fix RHSA-2026:67154
show 6 more
  • Red Hat Enterprise Linux BaseOS (v. 9) openssl 3.5.8-1.el9_8, openssl-libs 3.5.8-1.el9_8
    fixed: vendor fix RHSA-2026:67165
  • Red Hat Enterprise Linux BaseOS (v. 10) openssl 3.5.8-1.el10_2, openssl-libs 3.5.8-1.el10_2
    fixed: vendor fix RHSA-2026:67154
  • Red Hat Hardened Images openssl 3.5.8-0.1.hum1, openssl3 3.5.8-0.1.hum1, openssl-libs 3.5.8-0.1.hum1, openssl-perl 3.5.8-0.1.hum1, openssl3-libs 3.5.8-0.1.hum1, openssl-config-fips 3.5.8-0.1.hum1, +3 more
    fixed: vendor fix RHSA-2026:59641
  • Red Hat OpenShift Container Platform 4.22 rhcos 4.22.9.8.202611032353
    fixed: vendor fix RHSA-2026:95346
  • Red Hat Update Infrastructure 5 rhui5/cds-rhel9 1790241954, rhui5/rhua-rhel9 1790242004, rhui5/haproxy-rhel9 1790241900, rhui5/installer-rhel9 1789482961, rhui5/cds-kubernetes-rhel9 1789479916
    fixed: vendor fix RHSA-2026:67956
  • Red Hat Cert Manager support for Red Hat OpenShift release 1.20 cert-manager/jetstack-cert-manager-acmesolver-rhel9 1790223630 Red Hat Cost Management 4 costmanagement/costmanagement-metrics-operator-bundle 1790851152 Red Hat Developer Hub 1.10 rhdh/rhdh-rhel9-operator 1791219676, rhdh/rhdh-operator-bundle 1791315788, rhdh/rhdh-must-gather-rhel9 1788278523, rhdh/rhdh-rag-content-rhel9 1791168570 Red Hat Enterprise Linux 6 openssl, openssl-perl Red Hat Enterprise Linux 7 ovmf, OVMF, shim, AAVMF, mokutil, openssl, +5 more Red Hat Enterprise Linux 8 edk2, shim, openssl, shim-x64, edk2-ovmf, shim-aa64, +10 more
    +8 more products
    Red Hat Enterprise Linux 9 edk2, shim, shim-x64, edk2-ovmf, shim-aa64, edk2-tools, +4 more Red Hat Enterprise Linux 10 edk2, shim, shim-unsigned-x64, shim-unsigned-aarch64 Red Hat Hardened Images unbound Red Hat OpenShift AI (RHOAI) rhoai/odh-llama-stack-k8s-operator-rhel9 Red Hat OpenShift Container Platform 4 openshift/ose-rhel-coreos-8 Red Hat Satellite 6 puppet-agent, openvox-agent Red Hat Satellite Client puppet-agent, openvox-agent Red Hat Update Infrastructure 5 rhui5/cds-rhel9 1789479900, rhui5/rhua-rhel9 1789478095, rhui5/haproxy-rhel9 1789479891, rhui5/installer-rhel9 1790241922, rhui5/cds-kubernetes-rhel9 1790241897
    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
yes
Technical impact
partial
Assessed
2 mo ago

Exploit prediction

1.70% chance of exploitation in the next 30 days, higher than 77% of all scored CVEs (FIRST EPSS, 2026-11-08).

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
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products

  • OpenSSL OpenSSL

Classification

Weakness
Technology feeds

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.