# CVE-2026-42764 — OpenSSL

> As of 2026-06-10, CVE-2026-42764 is a HIGH-severity vulnerability in OpenSSL, CVSS v3.1 7.5, EPSS 0.7% (54.5th percentile). Threadlinqs Intelligence links 1 tracked threat campaign to CVE-2026-42764, most recently “HollowByte: OpenSSL Pre-Authentication TLS DoS Flaw Bloats Server Memory With 11-Byte Payload”.

**Last updated:** 2026-06-10

## What is CVE-2026-42764?

Issue summary: Receiving a QUIC initial packet with an invalid token may trigger a NULL pointer dereference in the OpenSSL QUIC server with address validation disabled. Impact summary: NULL pointer dereference typically causes abnormal termination of the affected QUIC server process and a Denial of Service. If the address validation is disabled in the OpenSSL QUIC server implementation, an attacker can crash the server by sending an initial packet with an invalid or expired token. By default, the client address validation is enabled in the OpenSSL QUIC server implementation, which makes the default configuration not vulnerable to this issue. However if the SSL_LISTENER_FLAG_NO_VALIDATE is used with the SSL_new_listener() call, the address validation is disabled making the vulnerable code reachable. The FIPS modules in 4.0, 3.6, 3.5, 3.4, and 3.0 are not affected by this issue, as the affected code is outside the OpenSSL FIPS module boundary.

The record classifies CVE-2026-42764 under weakness class [CWE-476](https://intel.threadlinqs.com/cwe/CWE-476). Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs no prior authentication, needs no user interaction, and has high impact on availability. 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 140 days ago.

## Severity and exploitation probability

- **CVSS v3.1 base score:** 7.5 — HIGH (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **EPSS (FIRST):** 0.7% probability of exploitation in the next 30 days, higher than 54.5% of all scored CVEs
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 5.9/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- **Published:** 2026-06-09, last modified 2026-06-10

## Is CVE-2026-42764 being exploited?

It currently carries a trending score of 19 in the Threadlinqs vulnerability feed.

## Affected products and versions

- [OpenSSL](https://intel.threadlinqs.com/vendors/openssl): OpenSSL

## How to fix CVE-2026-42764

No vendor patch reference has been recorded for CVE-2026-42764 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.

## Threat activity tracking CVE-2026-42764

1 tracked threat in the Threadlinqs corpus references CVE-2026-42764, either in the campaign’s CVE list or as an indicator on the campaign record.

- [HollowByte: OpenSSL Pre-Authentication TLS DoS Flaw Bloats Server Memory With 11-Byte Payload](https://intel.threadlinqs.com/threat/TL-2026-1457) — MEDIUM · 2026-07-17

## Sources

Enriched from CVE.org, FIRST EPSS, GitHub Security Advisories. Last verified by Threadlinqs on 2026-10-10.

**Vendor advisory and patch**

- [openssl-library.org — vendor advisory](https://openssl-library.org/news/secadv/20260609.txt)
- [github.com — patch](https://github.com/openssl/openssl/commit/bf29a458c1a231eca87e384c62b9c2553fa57a91)
- [github.com — patch (a45a0aba8095682c88ff4fc4a784892b8c6f0677)](https://github.com/openssl/openssl/commit/a45a0aba8095682c88ff4fc4a784892b8c6f0677)
- [github.com — patch (5e3ed291b8af0b03d5d3b9e56a1da69a187e9729)](https://github.com/openssl/openssl/commit/5e3ed291b8af0b03d5d3b9e56a1da69a187e9729)

Canonical: https://intel.threadlinqs.com/cve/CVE-2026-42764
Full detection coverage and IOCs for threats exploiting CVE-2026-42764 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp