# CVE-2026-63388: Libevent: Heap out-of-bounds write in bufferevent_socket_set_conn_address_ reachable via AF_UNIX accept

CVE-2026-63388 is fixed in 18 products on 1 platform, first by libevent-2.1-6 2.1.8-stable-4ubuntu0.1~esm2, released August 20, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-63388
- Priority: High
- CVSS: 8.6 (Important)
- EPSS: 0.0014
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Aug 20, 2026
- Weakness: Reachable Assertion
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-63388

## Description

Libevent is an event notification library. Prior to 2.1.13 and 2.2.2-alpha, libevent has a heap out-of-bounds write in bufferevent_sock.c when bufferevent_socket_set_conn_address_ copies a kernel-supplied AF_UNIX peer address into bufferevent_private.conn_address. Release builds compiled with NDEBUG disable the EVUTIL_ASSERT length guard, and the evhttp accept path can pass a 110-byte sockaddr from accept() into the 28-byte field. An unauthenticated local peer able to connect to an AF_UNIX listener can overwrite the adjacent dns_request pointer and heap data, causing memory corruption with confidentiality, integrity, and availability impact. This issue is fixed in versions 2.1.13 and 2.2.2-alpha.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | libevent Debian 12.15 (bookworm) | 2.1.12-stable-8+deb12u1 | [DEBIAN-CVE-2026-63388](https://patchblox.com/security/data/fix/linux/debian-cve-2026-63388.md) | Aug 21, 2026 |
| Linux | libevent Debian 13.5 (trixie) | 2.1.13-stable-1~deb13u1 | [DEBIAN-CVE-2026-63388](https://patchblox.com/security/data/fix/linux/debian-cve-2026-63388.md) | Aug 21, 2026 |
| Linux | libevent Debian 14 | 2.1.13-stable-1 | [DEBIAN-CVE-2026-63388](https://patchblox.com/security/data/fix/linux/debian-cve-2026-63388.md) | Aug 21, 2026 |
| Linux | libevent RHEL 10 | 2.1.13-1.el10_2 | [RHSA-2026:67909](https://patchblox.com/security/data/fix/linux/rhsa-2026-67909.md) | Sep 17, 2026 |
| Linux | libevent RHEL 8 | 0:2.1.8-11.el8_10 | [RHSA-2026:67908](https://patchblox.com/security/data/fix/linux/rhsa-2026-67908.md) | Sep 19, 2026 |
| Linux | libevent RHEL 9 | 0:2.1.13-1.el9_8 | [RHSA-2026:67910](https://patchblox.com/security/data/fix/linux/rhsa-2026-67910.md) | Sep 19, 2026 |
| Linux | libevent almalinux 10 | 2.1.13-1.el10_2 | [ALSA-2026:67909](https://patchblox.com/security/data/fix/linux/alsa-2026-67909.md) | Sep 16, 2026 |
| Linux | libevent almalinux 8 | 2.1.8-11.el8_10 | [ALSA-2026:67908](https://patchblox.com/security/data/fix/linux/alsa-2026-67908.md) | Sep 16, 2026 |
| Linux | libevent almalinux 9 | 2.1.13-1.el9_8 | [ALSA-2026:67910](https://patchblox.com/security/data/fix/linux/alsa-2026-67910.md) | Sep 16, 2026 |
| Linux | libevent ol 10 | 0:2.1.13-1.el10_2 | [ELSA-2026-67909](https://patchblox.com/security/data/fix/linux/elsa-2026-67909.md) | Sep 16, 2026 |
| Linux | libevent ol 8 | 0:2.1.8-11.el8_10 | [ELSA-2026-67908](https://patchblox.com/security/data/fix/linux/elsa-2026-67908.md) | Sep 17, 2026 |
| Linux | libevent ol 9 | 0:2.1.13-1.el9_8 | [ELSA-2026-67910](https://patchblox.com/security/data/fix/linux/elsa-2026-67910.md) | Sep 16, 2026 |
| Linux | libevent rocky 10 | 0:2.1.13-1.el10_2 | [RLSA-2026:67909](https://patchblox.com/security/data/fix/linux/rlsa-2026-67909.md) | Sep 17, 2026 |
| Linux | libevent rocky 8 | 0:2.1.8-11.el8_10 | [RLSA-2026:67908](https://patchblox.com/security/data/fix/linux/rlsa-2026-67908.md) | Sep 17, 2026 |
| Linux | libevent rocky 9 | 0:2.1.13-1.el9_8 | [RLSA-2026:67910](https://patchblox.com/security/data/fix/linux/rlsa-2026-67910.md) | Sep 17, 2026 |
| Linux | libevent-2.1-6 Ubuntu 18.04.6 LTS (bionic) | 2.1.8-stable-4ubuntu0.1~esm2 | [libevent-2.1-6 2.1.8-stable-4ubuntu0.1~esm2](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-libevent-2.1-6-2.1.8-stable-4ubuntu0.1-esm2.md) | Aug 20, 2026 |
| Linux | libevent-2.1-7 Ubuntu 20.04 LTS (focal) | 2.1.11-stable-1ubuntu0.1~esm2 | [libevent-2.1-7 2.1.11-stable-1ubuntu0.1~esm2](https://patchblox.com/security/data/fix/linux/ubuntu-focal-libevent-2.1-7-2.1.11-stable-1ubuntu0.1-esm2.md) | Aug 20, 2026 |
| Linux | libevent-2.1-7 Ubuntu 22.04.1 LTS (jammy) | 2.1.12-stable-1ubuntu0.2 | [libevent-2.1-7 2.1.12-stable-1ubuntu0.2](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-libevent-2.1-7-2.1.12-stable-1ubuntu0.2.md) | Aug 20, 2026 |
| Linux | libevent-2.1-7t64 Ubuntu 24.04.5 LTS (noble) | 2.1.12-stable-9ubuntu2.2 | [libevent-2.1-7t64 2.1.12-stable-9ubuntu2.2](https://patchblox.com/security/data/fix/linux/ubuntu-noble-libevent-2.1-7t64-2.1.12-stable-9ubuntu2.2.md) | Aug 20, 2026 |
| Linux | libevent-2.1-7t64 Ubuntu 26.04.1 LTS (resolute) | 2.1.12-stable-10ubuntu0.2 | [libevent-2.1-7t64 2.1.12-stable-10ubuntu0.2](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-libevent-2.1-7t64-2.1.12-stable-10ubuntu0.2.md) | Aug 20, 2026 |
| Linux | libevent-core-2.1-6 Ubuntu 18.04.6 LTS (bionic) | 2.1.8-stable-4ubuntu0.1~esm2 | [libevent-core-2.1-6 2.1.8-stable-4ubuntu0.1~esm2](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-libevent-core-2.1-6-2.1.8-stable-4ubuntu0.1-esm2.md) | Aug 20, 2026 |
| Linux | libevent-core-2.1-7 Ubuntu 20.04 LTS (focal) | 2.1.11-stable-1ubuntu0.1~esm2 | [libevent-core-2.1-7 2.1.11-stable-1ubuntu0.1~esm2](https://patchblox.com/security/data/fix/linux/ubuntu-focal-libevent-core-2.1-7-2.1.11-stable-1ubuntu0.1-esm2.md) | Aug 20, 2026 |
| Linux | libevent-core-2.1-7 Ubuntu 22.04.1 LTS (jammy) | 2.1.12-stable-1ubuntu0.2 | [libevent-core-2.1-7 2.1.12-stable-1ubuntu0.2](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-libevent-core-2.1-7-2.1.12-stable-1ubuntu0.2.md) | Aug 20, 2026 |
| Linux | libevent-core-2.1-7t64 Ubuntu 24.04.5 LTS (noble) | 2.1.12-stable-9ubuntu2.2 | [libevent-core-2.1-7t64 2.1.12-stable-9ubuntu2.2](https://patchblox.com/security/data/fix/linux/ubuntu-noble-libevent-core-2.1-7t64-2.1.12-stable-9ubuntu2.2.md) | Aug 20, 2026 |
| Linux | libevent-core-2.1-7t64 Ubuntu 26.04.1 LTS (resolute) | 2.1.12-stable-10ubuntu0.2 | [libevent-core-2.1-7t64 2.1.12-stable-10ubuntu0.2](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-libevent-core-2.1-7t64-2.1.12-stable-10ubuntu0.2.md) | Aug 20, 2026 |
| Linux | libevent-devel RHEL 8 | 0:2.1.8-11.el8_10 | [RHSA-2026:67908](https://patchblox.com/security/data/fix/linux/rhsa-2026-67908.md) | Sep 19, 2026 |
| Linux | libevent-devel RHEL 9 | 0:2.1.13-1.el9_8 | [RHSA-2026:67910](https://patchblox.com/security/data/fix/linux/rhsa-2026-67910.md) | Sep 19, 2026 |
| Linux | libevent-devel almalinux 10 | 2.1.13-1.el10_2 | [ALSA-2026:67909](https://patchblox.com/security/data/fix/linux/alsa-2026-67909.md) | Sep 16, 2026 |
| Linux | libevent-devel almalinux 8 | 2.1.8-11.el8_10 | [ALSA-2026:67908](https://patchblox.com/security/data/fix/linux/alsa-2026-67908.md) | Sep 16, 2026 |
| Linux | libevent-devel almalinux 9 | 2.1.13-1.el9_8 | [ALSA-2026:67910](https://patchblox.com/security/data/fix/linux/alsa-2026-67910.md) | Sep 16, 2026 |
| Linux | libevent-devel ol 10 | 0:2.1.13-1.el10_2 | [ELSA-2026-67909](https://patchblox.com/security/data/fix/linux/elsa-2026-67909.md) | Sep 16, 2026 |
| Linux | libevent-devel ol 8 | 0:2.1.8-11.el8_10 | [ELSA-2026-67908](https://patchblox.com/security/data/fix/linux/elsa-2026-67908.md) | Sep 17, 2026 |
| Linux | libevent-devel ol 9 | 0:2.1.13-1.el9_8 | [ELSA-2026-67910](https://patchblox.com/security/data/fix/linux/elsa-2026-67910.md) | Sep 16, 2026 |
| Linux | libevent-doc RHEL 8 | 0:2.1.8-11.el8_10 | [RHSA-2026:67908](https://patchblox.com/security/data/fix/linux/rhsa-2026-67908.md) | Sep 19, 2026 |
| Linux | libevent-doc RHEL 9 | 0:2.1.13-1.el9_8 | [RHSA-2026:67910](https://patchblox.com/security/data/fix/linux/rhsa-2026-67910.md) | Sep 19, 2026 |
| Linux | libevent-doc almalinux 10 | 2.1.13-1.el10_2 | [ALSA-2026:67909](https://patchblox.com/security/data/fix/linux/alsa-2026-67909.md) | Sep 16, 2026 |
| Linux | libevent-doc almalinux 8 | 2.1.8-11.el8_10 | [ALSA-2026:67908](https://patchblox.com/security/data/fix/linux/alsa-2026-67908.md) | Sep 16, 2026 |
| Linux | libevent-doc almalinux 9 | 2.1.13-1.el9_8 | [ALSA-2026:67910](https://patchblox.com/security/data/fix/linux/alsa-2026-67910.md) | Sep 16, 2026 |
| Linux | libevent-doc ol 10 | 0:2.1.13-1.el10_2 | [ELSA-2026-67909](https://patchblox.com/security/data/fix/linux/elsa-2026-67909.md) | Sep 16, 2026 |
| Linux | libevent-doc ol 8 | 0:2.1.8-11.el8_10 | [ELSA-2026-67908](https://patchblox.com/security/data/fix/linux/elsa-2026-67908.md) | Sep 17, 2026 |
| Linux | libevent-doc ol 9 | 0:2.1.13-1.el9_8 | [ELSA-2026-67910](https://patchblox.com/security/data/fix/linux/elsa-2026-67910.md) | Sep 16, 2026 |
| Linux | libevent-extra-2.1-6 Ubuntu 18.04.6 LTS (bionic) | 2.1.8-stable-4ubuntu0.1~esm2 | [libevent-extra-2.1-6 2.1.8-stable-4ubuntu0.1~esm2](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-libevent-extra-2.1-6-2.1.8-stable-4ubuntu0.1-esm2.md) | Aug 20, 2026 |
| Linux | libevent-extra-2.1-7 Ubuntu 20.04 LTS (focal) | 2.1.11-stable-1ubuntu0.1~esm2 | [libevent-extra-2.1-7 2.1.11-stable-1ubuntu0.1~esm2](https://patchblox.com/security/data/fix/linux/ubuntu-focal-libevent-extra-2.1-7-2.1.11-stable-1ubuntu0.1-esm2.md) | Aug 20, 2026 |
| Linux | libevent-extra-2.1-7 Ubuntu 22.04.1 LTS (jammy) | 2.1.12-stable-1ubuntu0.2 | [libevent-extra-2.1-7 2.1.12-stable-1ubuntu0.2](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-libevent-extra-2.1-7-2.1.12-stable-1ubuntu0.2.md) | Aug 20, 2026 |
| Linux | libevent-extra-2.1-7t64 Ubuntu 24.04.5 LTS (noble) | 2.1.12-stable-9ubuntu2.2 | [libevent-extra-2.1-7t64 2.1.12-stable-9ubuntu2.2](https://patchblox.com/security/data/fix/linux/ubuntu-noble-libevent-extra-2.1-7t64-2.1.12-stable-9ubuntu2.2.md) | Aug 20, 2026 |
| Linux | libevent-extra-2.1-7t64 Ubuntu 26.04.1 LTS (resolute) | 2.1.12-stable-10ubuntu0.2 | [libevent-extra-2.1-7t64 2.1.12-stable-10ubuntu0.2](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-libevent-extra-2.1-7t64-2.1.12-stable-10ubuntu0.2.md) | Aug 20, 2026 |
| Linux | libevent-openssl-2.1-6 Ubuntu 18.04.6 LTS (bionic) | 2.1.8-stable-4ubuntu0.1~esm2 | [libevent-openssl-2.1-6 2.1.8-stable-4ubuntu0.1~esm2](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-libevent-openssl-2.1-6-2.1.8-stable-4ubuntu0.1-esm2.md) | Aug 20, 2026 |
| Linux | libevent-openssl-2.1-7 Ubuntu 20.04 LTS (focal) | 2.1.11-stable-1ubuntu0.1~esm2 | [libevent-openssl-2.1-7 2.1.11-stable-1ubuntu0.1~esm2](https://patchblox.com/security/data/fix/linux/ubuntu-focal-libevent-openssl-2.1-7-2.1.11-stable-1ubuntu0.1-esm2.md) | Aug 20, 2026 |
| Linux | libevent-openssl-2.1-7 Ubuntu 22.04.1 LTS (jammy) | 2.1.12-stable-1ubuntu0.2 | [libevent-openssl-2.1-7 2.1.12-stable-1ubuntu0.2](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-libevent-openssl-2.1-7-2.1.12-stable-1ubuntu0.2.md) | Aug 20, 2026 |
| Linux | libevent-openssl-2.1-7t64 Ubuntu 24.04.5 LTS (noble) | 2.1.12-stable-9ubuntu2.2 | [libevent-openssl-2.1-7t64 2.1.12-stable-9ubuntu2.2](https://patchblox.com/security/data/fix/linux/ubuntu-noble-libevent-openssl-2.1-7t64-2.1.12-stable-9ubuntu2.2.md) | Aug 20, 2026 |
| Linux | libevent-openssl-2.1-7t64 Ubuntu 26.04.1 LTS (resolute) | 2.1.12-stable-10ubuntu0.2 | [libevent-openssl-2.1-7t64 2.1.12-stable-10ubuntu0.2](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-libevent-openssl-2.1-7t64-2.1.12-stable-10ubuntu0.2.md) | Aug 20, 2026 |
| Linux | libevent-pthreads-2.1-6 Ubuntu 18.04.6 LTS (bionic) | 2.1.8-stable-4ubuntu0.1~esm2 | [libevent-pthreads-2.1-6 2.1.8-stable-4ubuntu0.1~esm2](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-libevent-pthreads-2.1-6-2.1.8-stable-4ubuntu0.1-esm2.md) | Aug 20, 2026 |
| Linux | libevent-pthreads-2.1-7 Ubuntu 20.04 LTS (focal) | 2.1.11-stable-1ubuntu0.1~esm2 | [libevent-pthreads-2.1-7 2.1.11-stable-1ubuntu0.1~esm2](https://patchblox.com/security/data/fix/linux/ubuntu-focal-libevent-pthreads-2.1-7-2.1.11-stable-1ubuntu0.1-esm2.md) | Aug 20, 2026 |
| Linux | libevent-pthreads-2.1-7 Ubuntu 22.04.1 LTS (jammy) | 2.1.12-stable-1ubuntu0.2 | [libevent-pthreads-2.1-7 2.1.12-stable-1ubuntu0.2](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-libevent-pthreads-2.1-7-2.1.12-stable-1ubuntu0.2.md) | Aug 20, 2026 |
| Linux | libevent-pthreads-2.1-7t64 Ubuntu 24.04.5 LTS (noble) | 2.1.12-stable-9ubuntu2.2 | [libevent-pthreads-2.1-7t64 2.1.12-stable-9ubuntu2.2](https://patchblox.com/security/data/fix/linux/ubuntu-noble-libevent-pthreads-2.1-7t64-2.1.12-stable-9ubuntu2.2.md) | Aug 20, 2026 |
| Linux | libevent-pthreads-2.1-7t64 Ubuntu 26.04.1 LTS (resolute) | 2.1.12-stable-10ubuntu0.2 | [libevent-pthreads-2.1-7t64 2.1.12-stable-10ubuntu0.2](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-libevent-pthreads-2.1-7t64-2.1.12-stable-10ubuntu0.2.md) | Aug 20, 2026 |

---

Data as of 2026-11-10T01:44:33Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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