CVE-2026-40170
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.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.78%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
Description
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.
- CVSS 3.1
- 7.5 HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- EPSS
- 0.78% probability · 54th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-121, CWE-120
- Affected
- tatsuhiro-t/ngtcp2
- Source
- security-advisories@github.com
References
- https://github.com/ngtcp2/ngtcp2/commit/708a7640c1f48fb8ffb540c4b8ea5b4c1dfb8ee5Patch
- https://github.com/ngtcp2/ngtcp2/security/advisories/GHSA-f523-465f-8c8fExploit, Mitigation, Patch, Vendor Advisory
- http://www.openwall.com/lists/oss-security/2026/04/17/12Exploit, Mailing List, Mitigation, Patch, Third Party Advisory
- 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-8c8fExploit, Mitigation, Patch, Vendor Advisory
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-40170.json
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.