CVE-2026-40170VulnerabilityPublished 20 Apr 2026Updated 5 Oct 2026

Red Hat Security Advisory: Red Hat Hardened Images RPMs bug fix and enhancement update

Affects Red HatSource GCVE Database

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Not known to be exploited.

Data as of 30 Oct 2026, 11:52 UTC

Severity

High

Rated by Threat Radar · No CVSS score from NVD or the CNA

EPSS: 0.7% chance of exploitation in 30 days – higher than 55% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

Exploitation evidence

Disclosed: evidence found.
CVE published 20 Apr 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 30 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
Red Hat Product Security Red Hat	Affected >=9.8 >=10.2 Red Hat Red Hat Hardened Images aarch64 ngtcp2-main@aarch64 ngtcp2-0:1.22.1-1.hum1@aarch64	Fixed in–

AI-suggested

Red Hat advises disabling the qlog callback in applications using the ngtcp2 library to prevent the vulnerable code path from being exercised. This mitigation may reduce logging and debugging capabilities. Applications linked against ngtcp2 must be restarted after disabling qlog for the change to take effect. NodeJS packages shipped by Red Hat are not affected as QUIC support is disabled by default. For Samba on RHEL 9.8+ and 10.2+, consider disabling SMB over QUIC or applying updates when available. Patch status is not explicitly confirmed in the advisory; check Red Hat's official advisory for updates.

Description

This update includes the following RPMs: ngtcp2: * ngtcp2-1.22.1-1.hum1 (aarch64, x86_64) * ngtcp2-crypto-gnutls-1.22.1-1.hum1 (aarch64, x86_64) * ngtcp2-crypto-gnutls-devel-1.22.1-1.hum1 (aarch64, x86_64) * ngtcp2-crypto-ossl-1.22.1-1.hum1 (aarch64, x86_64) * ngtcp2-crypto-ossl-devel-1.22.1-1.hum1 (aarch64, x86_64) * ngtcp2-devel-1.22.1-1.hum1 (aarch64, x86_64) * ngtcp2-doc-1.22.1-1.hum1 (noarch) * ngtcp2-1.22.1-1.hum1.src (src)

Impact

The vulnerability allows a remote attacker to cause a denial of service by triggering a stack buffer overflow during the QUIC handshake when qlog is enabled. This results in application crashes or restarts, impacting availability. There is no reported impact on confidentiality or integrity. The affected functionality is experimental and disabled by default in NodeJS packages shipped by Red Hat, limiting exposure. Samba on certain RHEL versions that support SMB over QUIC is affected, potentially impacting services relying on this protocol.

Summary

CVE-2026-40170 is a stack buffer overflow vulnerability in the ngtcp2 library, triggered by processing specially crafted large transport parameters during the QUIC handshake when the qlog callback is enabled. This vulnerability can cause denial of service by writing beyond a fixed-size buffer. While the vulnerable code is present in some Red Hat packages, it is not compiled into the NodeJS binaries shipped by Red Hat, thus those are not affected. The vulnerability impacts Samba versions 4.23 and above included in RHEL 9.8+ and RHEL 10.2+, which support SMB over QUIC using ngtcp2. The vulnerability is tracked under CWE-120. Red Hat recommends disabling the qlog callback to mitigate the issue, which may reduce logging capabilities. No known exploits are reported in the wild.

CWE-120Buffer Copy without Checking Size of Input (Classic Buffer Overflow) (opens in a new tab)
Base weaknessLikelihood of exploit: HighCWE Top 25 (2025): #11
The product copies an input buffer to an output buffer without verifying that the size of the input buffer is less than the size of the output buffer.
Requirements · Language Selection
Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
Architecture and Design · Libraries or Frameworks
Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
Operation · Build and Compilation · Environment Hardening
Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index…
OWASP Cheat Sheets
Docker Security (opens in a new tab)
XML Security (opens in a new tab)
OWASP ASVS 4.0.3
V5.4.1 (opens in a new tab)
V14.1.2 (opens in a new tab)
V13.3.1 (opens in a new tab)
Attack patterns
Buffer Overflow via Environment Variables (opens in a new tab)
Overflow Buffers (opens in a new tab)
Client-side Injection-induced Buffer Overflow (opens in a new tab)
Filter Failure through Buffer Overflow (opens in a new tab)
MIME Conversion (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 16 Aug 2026, 17:46 UTC

WeaknessesCWE-120

Technical details

References

Community reviews

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