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OpenVPN CVE-2026-12996

| EUVDEUVD-2026-51239 MEDIUM
Out-of-bounds Read (CWE-125)
6.0
CVSS 4.0 · Vendor
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Severity by source

Vendor (CNA) PRIMARY
6.0 MEDIUM
CVSS:4.0/AV:N/AC:H/AT:P/PR:L/UI:N/VC:L/VI:N/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
vuln.today AI
5.9 MEDIUM

Network-reachable authenticated race condition (PR:L, AC:H); server crash is primary impact (A:H) with minor freed-memory read exposure (C:L); no integrity or scope change.

3.1 AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:H
4.0 AV:N/AC:H/AT:P/PR:L/UI:N/VC:L/VI:N/VA:H/SC:N/SI:N/SA:N
SUSE
5.9 MEDIUM
AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:H
Red Hat
5.9 MEDIUM
qualitative

Primary rating from Vendor (CNA).

CVSS VectorVendor

Attack Vector
Network
Attack Complexity
High
Privileges Required
Low
User Interaction
None
Scope
X

Lifecycle Timeline

5
Source Code Evidence Fetched
Jul 30, 2026 - 17:31 vuln.today
Analysis Generated
Jul 30, 2026 - 17:31 vuln.today
CVSS changed
Jul 30, 2026 - 17:22 NVD
6.0 (MEDIUM)
CVE Published
Jul 02, 2026 - 10:57 github-releases
MEDIUM 6.0
CVE Published
Jul 02, 2026 - 10:57 github-releases
UNKNOWN (no severity yet)

Description PRE-NVD

Disclosed via GitHub release of openvpn/openvpn. NVD scoring and full description are pending.

AnalysisAI

Use-after-free in OpenVPN's ack_write_buf() function allows an authenticated network client to crash the VPN server or potentially read freed heap memory by delivering a precisely-timed sequence of control channel and authentication packets. Affected releases span the 2.6.x and 2.7.x branches, with fixes shipping in v2.6.21 and v2.7.5 on July 1, 2026. No public exploit code or CISA KEV listing has been identified at time of analysis, and the AC:H/PR:L requirements materially limit realistic exploitation.

Technical ContextAI

OpenVPN's control channel handles key exchange, session negotiation, and acknowledgment buffering between peers. The vulnerability resides in ack_write_buf(), the function responsible for queuing acknowledgment packets within the control channel. A use-after-free (CWE-416 per description - though the NVD-assigned CWE is CWE-125, Out-of-bounds Read, likely reflecting the memory-read aspect of freed heap access) occurs when a race condition between the arrival of control channel packets and authentication packets causes ack_write_buf() to operate on already-freed memory. This freed-memory access can produce reads of stale heap content (explaining VC:L in the CVSS 4.0 vector) and, more reliably, corrupts process state leading to a server crash (VA:H). The bug was independently discovered by three researchers - 章鱼哥, Haiyang Huang, and Haruki Oyama - a convergence that suggests the code path is reachable via standard client behavior rather than requiring obscure protocol manipulation.

RemediationAI

Upgrade to OpenVPN v2.7.5 (2.7.x users) or v2.6.21 (2.6.x users), both released July 1, 2026 and available at https://github.com/OpenVPN/openvpn/releases/tag/v2.7.5 and documented at https://community.openvpn.net/Security%20Announcements/CVE-2026-12996. Ubuntu system administrators should apply USN-8540-1 via standard package management. If immediate patching is operationally blocked, the most effective compensating control is to restrict which authenticated identities can reach the OpenVPN control channel - for example, enforcing strict certificate pinning and revoking certificates for any untrusted or external clients, reducing the population of principals capable of triggering the race. Rate-limiting or connection throttling at the network edge will not prevent exploitation since the timing window is within a single session, not across many connections. No configuration knob disables ack_write_buf() independently. These workarounds are partial mitigations only; patching remains the definitive fix.

CVE-2018-7544 CRITICAL POC
9.1 Mar 16

A cross-protocol scripting issue was discovered in the management interface in OpenVPN through 2.4.5. Rated critical sev

CVE-2017-7478 HIGH POC
7.5 May 15

OpenVPN version 2.3.12 and newer is vulnerable to unauthenticated Denial of Service of server via received large control

CVE-2018-9336 HIGH POC
7.8 May 01

openvpnserv.exe (aka the interactive service helper) in OpenVPN 2.4.x before 2.4.6 allows a local attacker to cause a do

CVE-2023-46850 CRITICAL
9.8 Nov 11

Use after free in OpenVPN version 2.6.0 to 2.6.6 may lead to undefined behavoir, leaking memory buffers or remote execut

CVE-2019-25429 MEDIUM POC
6.1 Feb 19

Comodo Dome Firewall 2.7.0 contains a reflected cross-site scripting vulnerability that allows attackers to inject malic

CVE-2019-25428 MEDIUM POC
6.1 Feb 19

Comodo Dome Firewall 2.7.0 contains multiple reflected cross-site scripting vulnerabilities in the openvpn_users endpoin

CVE-2017-12166 CRITICAL
9.8 Oct 04

OpenVPN versions before 2.3.3 and 2.4.x before 2.4.4 are vulnerable to a buffer overflow vulnerability when key-method 1

CVE-2024-27903 CRITICAL
9.8 Jul 08

OpenVPN plug-ins on Windows with OpenVPN 2.6.9 and earlier could be loaded from any directory, which allows an attacker

CVE-2022-0547 CRITICAL
9.8 Mar 18

OpenVPN 2.1 until v2.4.12 and v2.5.6 may enable authentication bypass in external authentication plug-ins when more than

CVE-2020-7224 CRITICAL
9.8 Apr 16

The Aviatrix OpenVPN client through 2.5.7 on Linux, macOS, and Windows is vulnerable when OpenSSL parameters are altered

CVE-2025-12106 CRITICAL
9.1 Dec 01

Insufficient argument validation in OpenVPN 2.7_alpha1 through 2.7_rc1 allows an attacker to trigger a heap buffer over-

CVE-2024-4877 HIGH
8.8 Apr 03

OpenVPN version 2.4.0 through 2.6.10 on Windows allows an external, lesser privileged process to create a named pipe whi

Vendor StatusVendor

SUSE

Severity: Moderate
Product Status
SUSE Linux Enterprise Desktop 15 SP7 Affected
SUSE Linux Enterprise High Performance Computing 12 Affected
SUSE Linux Enterprise High Performance Computing 15 SP7 Affected
SUSE Linux Enterprise Module for Basesystem 15 SP7 Affected
SUSE Linux Enterprise Server 15 SP7 Affected

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CVE-2026-12996 vulnerability details – vuln.today

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