Bug 2459061 (CVE-2026-40170)

Summary:	CVE-2026-40170 ngtcp2: ngtcp2: Denial of service via stack buffer overflow during QUIC handshake
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security DevOps Team <prodsec-dev>
Status:	NEW ---	QA Contact:
Severity:	high	Docs Contact:
Priority:	high
Version:	unspecified	CC:	rhel-process-autobot, watson-tool-maintainers
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	---
Doc Text:	A flaw was found in ngtcp2, a C implementation of the IETF QUIC (Quick UDP Internet Connections) protocol. A remote attacker can exploit a stack buffer overflow vulnerability by sending specially crafted, large transport parameters during the QUIC handshake. This occurs when the qlog callback is enabled and untrusted peer transport parameters are processed, leading to writes beyond a fixed-size buffer. This can result in a denial of service.	Story Points:	---
Clone Of:		Environment:
Last Closed:		Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:	2459282, 2459283
Bug Blocks:

Description OSIDB Bzimport 2026-04-16 22:01:19 UTC

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.

Comment 9 errata-xmlrpc 2026-06-03 20:58:05 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 10

Via RHSA-2026:22963 https://access.redhat.com/errata/RHSA-2026:22963

Comment 10 errata-xmlrpc 2026-06-10 11:14:53 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 9

Via RHSA-2026:25049 https://access.redhat.com/errata/RHSA-2026:25049

Comment 11 TEJ RATHI 2026-06-23 06:13:30 UTC

```

For Samba package, this vulnerability strictly affects environments running Red Hat Enterprise Linux (RHEL) 9.8 and newer, as well as RHEL 10.2 and newer. Only these versions ship with Samba 4.23 or above, which introduces native support for the integrated ngtcp2 library to handle SMB over QUIC functionality. Earlier versions of RHEL utilize older iterations of Samba that do not bundle or support ngtcp2 and are therefore unaffected.

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