CVE-2026-40170
Description
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.
Statement
This Important vulnerability affects ngtcp2 when qlog is enabled and processing untrusted QUIC peer transport parameters, leading to a denial of service. In the context of Red Hat support products ngtcp2 is not shipped directly through any RPM package or supported product but is shipped as a bundled dependency by the nodejs packages to provide QUIC support. This feature is considered experimental by the NodeJS upstream and needs to be enabled during NodeJS's compilation time through (--with-quic configuration option), with that in mind the versions of NodeJS as shipped with Red Hat Enterprise Linux are not affected by this vulnerability as QUIC support is not enabled in the distributed supported packages. This means although the affected code is present in the package code base itself, it's not compiled when the package is built and therefore is not present in the final binary.
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.
Mitigation
To mitigate this issue, disable the `qlog` callback in applications utilizing the ngtcp2 library. This action prevents the vulnerable code path from being exercised when processing untrusted QUIC peer transport parameters. Disabling `qlog` may impact logging and debugging capabilities. Applications linked against ngtcp2 must be restarted for the change to take effect.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.5 | N/A | 7.5 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | Low | N/A | Low |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | None | N/A | None |
| Integrity Impact | None | N/A | None |
| Availability Impact | High | N/A | High |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Integrity,Confidentiality,Availability
Technical Impact: Modify Memory; Execute Unauthorized Code or Commands
Buffer overflows often can be used to execute arbitrary code, which is usually outside the scope of the product's implicit security policy. This can often be used to subvert any other security service.
Availability
Technical Impact: Modify Memory; DoS: Crash, Exit, or Restart; DoS: Resource Consumption (CPU)
Buffer overflows generally lead to crashes. Other attacks leading to lack of availability are possible, including putting the product into an infinite loop.
Frequently Asked Questions
Not sure what something means? Check out our Security Glossary.
Want to get errata notifications? Sign up here.
