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Fencer Vulns
high 7.5

CVE-2026-40170 json

ngtcp2 has a qlog transport parameter serialization stack buffer overflow

published 2026-04-16 6 mo ago modified 2026-07-15 3 mo ago also EUVD-2026-23302

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.8%
EPSS 0.8% chance of exploitation in 30 days, percentile 56%
public exploits
0
none known

Summary

ngtcp2 is a C implementation of the IETF QUIC protocol. In versions prior to 1.22.1, ngtcp2_qlog_parameters_set_transport_params() serializes peer transport parameters into a fixed 1024-byte stack buffer without bounds checking. When qlog is enabled, a remote peer can send sufficiently large transport parameters during the QUIC handshake to cause writes beyond the buffer boundary, resulting in a stack buffer overflow. This affects deployments that enable the qlog callback and process untrusted peer transport parameters. This issue has been fixed in version 1.22.1. If developers are unable to immediately upgrade, they can disable the qlog on client.

Patch / fix

  • Red Hat Red Hat Enterprise Linux 10 0:4.23.5-109.el10_2
  • Red Hat Red Hat Enterprise Linux 9 0:4.23.5-10.el9_8
  • Red Hat Red Hat Hardened Images 1.22.1-1.hum1
  • ngtcp2 Debian 12 0.12.1+dfsg-1+deb12u1
  • ngtcp2 Debian 13 1.11.0-1+deb13u1
  • ngtcp2 Debian 14 1.22.1-1

debian advisories DEBIAN-CVE-2026-40170

  • ngtcp2 Ubuntu 24.04 LTS 0.12.1+dfsg-1+deb12u1build0.24.04.1
  • ngtcp2 Ubuntu 25.10 1.11.0-1+deb13u1build0.25.10.1
  • ngtcp2 Ubuntu 26.04 LTS 1.16.0-1ubuntu0.1
  • ngtcp2 Ubuntu Pro 22.04 LTS 0.1.0+dfsg-1ubuntu0.1~esm1

ubuntu advisories UBUNTU-CVE-2026-40170

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

  • samba RHEL 9 4.23.5-10.el9_8
  • ctdb RHEL 9 4.23.5-10.el9_8
  • libldb RHEL 9 4.23.5-10.el9_8
  • ldb-tools RHEL 9 4.23.5-10.el9_8
  • libnetapi RHEL 9 4.23.5-10.el9_8
  • samba-libs RHEL 9 4.23.5-10.el9_8
  • samba-pidl RHEL 9 4.23.5-10.el9_8
  • samba-test RHEL 9 4.23.5-10.el9_8

red hat advisories RHSA-2026:25049RHSA-2026:22963RHSA-2026:9113

  • nodejs20 SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE High Performance Computing 15 SP5-LTSS +1 more 20.20.2-150500.11.30.1
  • nodejs24 SLES for SAP applications 16.0, SLES 16.0 24.18.0-160000.1.1
  • nodejs22 SLE Module for Web and Scripting 15 SP7 22.23.0-150700.3.12.1
  • nodejs24 SLE Module for Web and Scripting 15 SP7 24.17.0-150700.15.11.1
  • nodejs22 SLES for SAP applications 16.0, SLES 16.0 22.23.0-160000.1.1
  • nodejs20 SLES for SAP 15 SP6, SLES 15 SP6-LTSS 20.20.2-150600.3.21.1
  • nodejs22 SLES for SAP 15 SP6, SLES 15 SP6-LTSS 22.23.0-150600.13.18.1

suse advisories SUSE-SU-2026:3930-1SUSE-SU-2026:3929-1SUSE-SU-2026:22565-1SUSE-SU-2026:2695-1SUSE-SU-2026:2647-1SUSE-SU-2026:2633-1

  • nodejs24 openSUSE Leap 16.0 24.18.0-160000.1.1
  • nodejs22 openSUSE Leap 16.0 22.23.0-160000.1.1
  • nodejs24 openSUSE Tumbleweed 24.17.0-1.1
  • samba openSUSE Tumbleweed 4.23.8+git.477.f78166bceed-1.1
  • ngtcp2 openSUSE Tumbleweed 1.22.1-1.1

opensuse advisories openSUSE-SU-2026:21236-1openSUSE-SU-2026:21058-1openSUSE-SU-2026:11121-1openSUSE-SU-2026:10884-1openSUSE-SU-2026:10621-1

  • samba AlmaLinux 9 4.23.5-10.el9_8
  • libldb AlmaLinux 9 4.23.5-10.el9_8
  • ldb-tools AlmaLinux 9 4.23.5-10.el9_8
  • libnetapi AlmaLinux 9 4.23.5-10.el9_8
  • samba-libs AlmaLinux 9 4.23.5-10.el9_8
  • samba-pidl AlmaLinux 9 4.23.5-10.el9_8
  • samba-test AlmaLinux 9 4.23.5-10.el9_8
  • libwbclient AlmaLinux 9 4.23.5-10.el9_8

almalinux advisories ALSA-2026:25049ALSA-2026:22963

  • samba Rocky Linux 9 4.23.5-10.el9_8
  • samba Rocky Linux 10 4.23.5-109.el10_2

rocky linux advisories RLSA-2026:25049RLSA-2026:22963

  • ngtcp2 Alpine 3.20 1.5.0-r1
  • ngtcp2 Alpine 3.21 1.9.1-r1
  • ngtcp2 Alpine 3.22 1.12.0-r1
  • ngtcp2 Alpine 3.24, Alpine 3.23 1.22.1-r0

alpine advisories ALPINE-CVE-2026-40170

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-2026-40170 updated cvss 7.5

ngtcp2: ngtcp2: Denial of service via stack buffer overflow during QUIC handshake

  • Red Hat Enterprise Linux AppStream (v. 9) samba-client 4.23.5-10.el9_8, samba-winexe 4.23.5-10.el9_8, samba-gpupdate 4.23.5-10.el9_8, samba-vfs-iouring 4.23.5-10.el9_8, samba-krb5-printing 4.23.5-10.el9_8, samba-winbind-clients 4.23.5-10.el9_8, +1 more
    fixed: vendor fix RHSA-2026:25049
  • Red Hat Enterprise Linux AppStream (v. 10) samba-client 4.23.5-109.el10_2, samba-winexe 4.23.5-109.el10_2, samba-gpupdate 4.23.5-109.el10_2, samba-vfs-iouring 4.23.5-109.el10_2, samba-krb5-printing 4.23.5-109.el10_2, samba-winbind-clients 4.23.5-109.el10_2, +1 more
    fixed: vendor fix RHSA-2026:22963
  • Red Hat Enterprise Linux BaseOS (v. 9) samba 4.23.5-10.el9_8, libldb 4.23.5-10.el9_8, ldb-tools 4.23.5-10.el9_8, libnetapi 4.23.5-10.el9_8, samba-libs 4.23.5-10.el9_8, libwbclient 4.23.5-10.el9_8, +15 more
    fixed: vendor fix RHSA-2026:25049
  • Red Hat Enterprise Linux BaseOS (v. 10) samba 4.23.5-109.el10_2, libldb 4.23.5-109.el10_2, ldb-tools 4.23.5-109.el10_2, libnetapi 4.23.5-109.el10_2, samba-libs 4.23.5-109.el10_2, libwbclient 4.23.5-109.el10_2, +15 more
    fixed: vendor fix RHSA-2026:22963
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 9) samba-pidl 4.23.5-10.el9_8, samba-test 4.23.5-10.el9_8, samba-test-libs 4.23.5-10.el9_8, python3-samba-test 4.23.5-10.el9_8
    fixed: vendor fix RHSA-2026:25049
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) samba-pidl 4.23.5-109.el10_2, samba-test 4.23.5-109.el10_2, samba-test-libs 4.23.5-109.el10_2, python3-samba-test 4.23.5-109.el10_2
    fixed: vendor fix RHSA-2026:22963
  • Red Hat Enterprise Linux Resilient Storage (v. 9) ctdb 4.23.5-10.el9_8
    fixed: vendor fix RHSA-2026:25049
  • Red Hat Hardened Images ngtcp2 1.22.1-1.hum1, ngtcp2-crypto-ossl 1.22.1-1.hum1, ngtcp2-crypto-gnutls 1.22.1-1.hum1
    fixed: vendor fix RHSA-2026:9113
show 1 more
  • Red Hat Enterprise Linux 8 npm, nodejs, nodejs-libs, nodejs-nodemon, nodejs-full-i18n, nodejs-packaging, +1 more Red Hat Enterprise Linux 9 npm, nodejs, nodejs-libs, nodejs-full-i18n Red Hat Enterprise Linux 10 nodejs22, nodejs24
    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
yes
Technical impact
partial
Assessed
6 mo ago

Exploit prediction

0.78% chance of exploitation in the next 30 days, higher than 56% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/ngtcp2/ngtcp2/security/advisories/GHSA-f523-465f-8c8f referenced PoC, tagged "exploit" by a source, unverified
  • openwall.com http://www.openwall.com/lists/oss-security/2026/04/17/12 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

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

Affected products

  • ngtcp2 ngtcp2
  • Red Hat Red Hat Enterprise Linux 10
  • Red Hat Red Hat Enterprise Linux 9
  • Red Hat Red Hat Hardened Images
  • Red Hat Red Hat Enterprise Linux 8

Classification

Weakness
  • CWE-121 Stack-based Buffer Overflow
  • CWE-120 Buffer Copy without Checking Size of Input

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.