CVE-2026-40170
What it is
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.
At a glance
- Exploitability
- Can be exploited over the network without logging in. High risk of service disruption.
- Exploit odds
- 0.8% chance of exploitation in the next 30 days (EPSS).
- Fix
- A patch, advisory or fixed version is referenced. Upgrade or apply it.
Timeline
- PublishedDisclosed publicly on CVE.org and NVD
- Last updatedMost recent change to the record
Why it ranks here
- Exploited in the wild: no, CISA does not list it.
- Exploit odds: 0.8% in the next 30 days (EPSS).
- Severity: 7.5 HIGH (CVSS).
- Fix: a patch or advisory is linked.
Details
- Published
- Last modified
- Exploit probability
- 0.8% · EPSS, next 30 days
- Weakness
- CWE-121
- Record status
- Modified
Affected
- tatsuhiro-t ngtcp2 < 1.22.1
Attack profile CVSS 3.1 · 7.5
- Attack vector
- Network
- Complexity
- Low
- Privileges needed
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Is it in your code?
Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.
Read https://cve-list.com/agent/cve/CVE-2026-40170.md and follow it. Check whether this project is affected by CVE-2026-40170. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.
Fix and advisories
- https://github.com/ngtcp2/ngtcp2/commit/708a7640c1f48fb8ffb540c4b8ea5b4c1dfb8ee5
- https://github.com/ngtcp2/ngtcp2/security/advisories/GHSA-f523-465f-8c8f
- http://www.openwall.com/lists/oss-security/2026/04/17/12
- https://github.com/ngtcp2/ngtcp2/security/advisories/GHSA-f523-465f-8c8f
References
- https://github.com/ngtcp2/ngtcp2/commit/708a7640c1f48fb8ffb540c4b8ea5b4c1dfb8ee5
- https://github.com/ngtcp2/ngtcp2/security/advisories/GHSA-f523-465f-8c8f
- http://www.openwall.com/lists/oss-security/2026/04/17/12
- https://access.redhat.com/errata/RHSA-2026:22963
- https://access.redhat.com/errata/RHSA-2026:25049
- https://access.redhat.com/errata/RHSA-2026:9113
- https://access.redhat.com/security/cve/CVE-2026-40170
- https://bugzilla.redhat.com/show_bug.cgi?id=2459061
- https://github.com/ngtcp2/ngtcp2/security/advisories/GHSA-f523-465f-8c8f
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-40170.json