HighPublic exploit

Stack buffer overflow in ngtcp2 qlog transport parameter serialization

IdentifiersCVE-2026-40170CWE-121· Stack-based Buffer Overflow

CVE-2026-40170 affects ngtcp2, a C implementation of the IETF QUIC protocol. In versions prior to 1.22.1, the function ngtcp2_qlog_parameters_set_transport_params() serializes peer transport parameters into a fixed 1024-byte stack buffer without performing bounds checking. When qlog is enabled, a remote peer can supply sufficiently large transport parameters during the QUIC handshake, causing writes past the end of the stack buffer and triggering a stack-based buffer overflow. The issue affects deployments that enable the qlog callback and process untrusted peer transport parameters during handshake processing.

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ANALYST BRIEF

Impact, mitigation & remediation

What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.

Impact

What an attacker gets, and what they’ve been doing with it.

Successful exploitation can cause a denial of service by crashing the affected process during the QUIC handshake as a result of stack memory corruption. Based on the provided information, the documented impact is denial of service; no verified information was provided establishing reliable remote code execution.

Mitigation

If you can’t patch tonight, do this now.

If an immediate upgrade is not possible, disable qlog, specifically on the client as noted in the provided content. More generally, avoid enabling qlog in deployments that process untrusted peer transport parameters until the fixed version is deployed.

Remediation

Patch, then assume compromise.

Upgrade ngtcp2 to version 1.22.1 or later, where the issue is fixed. Ensure all affected applications and bundled third-party copies of ngtcp2 are updated accordingly.

PUBLIC EXPLOITS

Exploits

No public exploits tracked yet. Mallory keeps watching.

VALID 0 / 0 TOTALView more in app

No public exploit code observed for this vulnerability.

EXPOSURE SURFACE

Affected products & vendors

Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.

VendorProductType

DebianNgtcp2application

Nghttp2Ngtcp2application

Tatsuhiro-TNgtcp2application

Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.

ACTIVITY FEED

Recent activity

7 sources tracked across advisories and community write-ups. News coverage will land here when it surfaces.

7 SOURCESView more in app

No news coverage yet. Advisories and community discussion only.

What this page doesn’t show

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Exposure mapping

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Threat actor evidence

Every observed campaign linking this CVE to a named adversary.

Associated malware

Malware families riding this exploit, with evidence and IOCs.

Detection signatures

YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.

Vendor-by-vendor mapping

Cross-references every affected SKU, including bundled OEM variants.

Social activity4