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Fencer Vulns
medium 5.3

CVE-2026-75804 json

QUIC Connection-Level Flow Control is Not Enforced for Streams

published 2026-09-29 40 d ago modified 2026-10-08 32 d ago also EUVD-2026-89009

cvss
5.3
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 45%
public exploits
0
none known

Summary

Issue summary: OpenSSL QUIC stack does not enforce connection level flow control for streams. Remote peers may send more bytes as long as they fit within the stream flow control limits.

Impact summary: A malicious remote peer may exploit the lack of connection flow control for streams to make the QUIC stack receive ~100MB of memory instead of 768 KiB (default flow control window size).

CWE: CWE-770: Allocation of Resources Without Limits or Throttling

Description: The local QUIC stack advertises two flow control limits to its remote peer: stream flow control limit and connection flow control limit. The remote peer must follow both limits when transmitting stream data.

Whenever the local QUIC stack receives a stream frame, it validates that the size of the received stream frame stays within flow control limits. If either limit is exceeded (stream level or connection level), then the QUIC stack must close the connection with a flow control error.

The vulnerable OpenSSL QUIC stack enforces the stream-level but not the connection-level limit. To exploit the issue, three conditions must be met: - the remote peer opens several streams - each stream must stay within the stream-level flow control limit - there must be no zero-offset byte sent on any of the streams (to prevent the vulnerable QUIC stack from consuming data). By meeting the conditions above, the remote peer may make the local stack allocate 2 x MAX_STREAMS x (stream flow control limit) bytes of memory. MAX_STREAMS defaults to 100, and the limit applies to both bidirectional and unidirectional streams, making it 200 in total. The default flow control window for a stream is 512kB. The remote peer may force the vulnerable QUIC stack to allocate 100MB of heap per connection.

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 3.4.8, 3.5.9, 3.6.5, 4.0.3
  • openssl Debian 13 3.5.7-1~deb13u3
  • openssl Debian 14 3.6.5-1

debian advisories DEBIAN-CVE-2026-75804

  • openssl Ubuntu 26.04 LTS 3.5.5-1ubuntu3.6

ubuntu advisories UBUNTU-CVE-2026-75804

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

  • openssl3 hummingbird 1 3.5.9-0.1.hum1
  • openssl3-libs hummingbird 1 3.5.9-0.1.hum1
  • openssl3-devel-engine hummingbird 1 3.5.9-0.1.hum1
  • openssl hummingbird 1 3.5.9-0.1.hum1
  • openssl-libs hummingbird 1 3.5.9-0.1.hum1
  • openssl-perl hummingbird 1 3.5.9-0.1.hum1
  • openssl-config-fips hummingbird 1 3.5.9-0.1.hum1
  • openssl-devel-engine hummingbird 1 3.5.9-0.1.hum1

red hat advisories RHSA-2026:74166RHSA-2026:74162

  • openssl-3 SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 3.5.0-160000.11.1
  • openssl-3 SLE Module for Basesystem 15 SP7 3.5.0-150700.5.53.2

suse advisories SUSE-SU-2026:24188-1SUSE-SU-2026:24245-1SUSE-SU-2026:4414-1

  • openssl-3 openSUSE Leap 16.0 3.5.0-160000.11.1

opensuse advisories openSUSE-SU-2026:22102-1

  • openssl Alpine 3.21 3.3.7-r2

alpine advisories ALPINE-CVE-2026-75804

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

  • openssl Azure Linux 3.0 3.3.7-7

azure linux advisories AZL-105594

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-2026-75804 updated cvss 5.3

openssl: OpenSSL: Denial of Service via unenforced QUIC connection flow control

  • Red Hat OpenShift Developer Tools and Services ocp-tools-4/jenkins-rhel9 Red Hat Developer Hub 1 rhdh/rhdh-hub-rhel9
    affected: workaround, no fix available
  • Red Hat Enterprise Linux 6 openssl, openssl-perl, openssl 3.5.8-1.el10_2 Red Hat Enterprise Linux 7 ovmf, OVMF, AAVMF, openssl, openssl-libs, openssl-perl, +1 more Red Hat Enterprise Linux 8 openssl, edk2-ovmf, edk2-aarch64, openssl-libs, openssl-perl, mingw-openssl, +9 more Red Hat Enterprise Linux 9 openssl, shim-x64, shim-aa64, openssl-libs, openssl-perl, compat-openssl11, +5 more Red Hat Enterprise Linux 10 shim 16.1-4.el10, openssl 3.5.8-1.el10_2, edk2 20251114-5.el10_2.2, shim-unsigned-x64 16.1-1.el10, shim-unsigned-aarch64 16.1-2.el10 Red Hat Hardened Images unbound 1.26.1-1.hum1
    affected: workaround, no fix available “Fix deferred”
  • Red Hat JBoss Core Services jbcs-httpd24-openssl, jbcs-httpd24-openssl-libs, jbcs-httpd24-openssl-perl Red Hat OpenShift Container Platform 4 openshift/ose-rhel-coreos-8, openshift/ose-rhel-coreos-9 Red Hat OpenShift Container Platform 5 openshift/ose-rhel-coreos-9
    affected: workaround, no fix available
  • Red Hat OpenShift Dev Spaces devspaces/dashboard-rhel9
    affected: workaround, no fix available “Fix deferred”
  • Red Hat Enterprise Linux 9 edk2-ovmf, edk2-tools, edk2-aarch64, edk2 20251114-5.el10_2.2 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 openssl 3.5.9-0.1.hum1, openssl3 3.5.9-0.1.hum1, openssl-libs 3.5.9-0.1.hum1, openssl-perl 3.5.9-0.1.hum1, openssl3-libs 3.5.9-0.1.hum1, openssl-config-fips 3.5.9-0.1.hum1, +3 more
    fixed: vendor fix RHSA-2026:74162
  • Red Hat Enterprise Linux 7 shim, mokutil, shim-x64, shim-ia32, shim-signed Red Hat Enterprise Linux 8 shim-x64, shim-aa64, shim-ia32, shim 16.1-4.el10 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 Red Hat Satellite 6 puppet-agent, openvox-agent 8.28.1-1.el9sat
    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
40 d ago

Exploit prediction

0.53% chance of exploitation in the next 30 days, higher than 45% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CISA ADP 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
CNA 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Affected products

  • OpenSSL OpenSSL

Classification

Weakness
  • CWE-770 Allocation of Resources Without Limits or Throttling
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.