--- title: "CVE-2026-103415: TLS 1.3 Client - Buffer Overflow" description: "TLS 1.3 clients copy the server's cookie from HelloRetryRequest into the second ClientHello without validating cookie size, causing a buffer overflow before certificate authentication, letting malicious servers overwrite memory." url: https://panop.io/threat-heartbeat/CVE-2026-103415/ --- # CVE-2026-103415 TLS 1.3 Client - Buffer Overflow TLS 1.3 clients copy the server's cookie from HelloRetryRequest into the second ClientHello without validating cookie size, causing a buffer overflow before certificate authentication, letting malicious servers overwrite memory. CVSS base score 9.3 /10 Critical CISA KEV Not listed Public exploit None known Authentication Not required [View the NVD record ↗](https://nvd.nist.gov/vuln/detail/CVE-2026-103415) ## Details Type Buffer Overflow Impact Remote Code Execution, Denial Of Service CVSS vector CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X Published 14 October 2026 Updated 15 October 2026 Weakness [CWE-787](https://cwe.mitre.org/data/definitions/787.html) ## Vendor fix Update to the latest TLS 1.3 client implementation that validates cookie size before copying. Patching closes this CVE. It does not tell you which of your systems run the affected version, or what else is exposed alongside them. ## References - [https://nvd.nist.gov/vuln/detail/CVE-2026-103415](https://nvd.nist.gov/vuln/detail/CVE-2026-103415) - [https://github.com/eclipse-threadx/netxduo/security/advisories/GHSA-5pv3-rhf5-gwgq](https://github.com/eclipse-threadx/netxduo/security/advisories/GHSA-5pv3-rhf5-gwgq) - [https://gitlab.eclipse.org/security/cve-assignment/-/work\_items/357](https://gitlab.eclipse.org/security/cve-assignment/-/work_items/357) [← All CVEs](https://panop.io/threat-heartbeat/) ## What this record can't tell you - Whether you run the affected software, and where - Whether an attacker can actually reach and exploit it - The misconfigurations that never get a CVE number - What it would cost the business, ranked into what to fix first Panop answers these inside your environment, for this CVE and every other finding. [Book a demo](https://panop.io/demo)