Quick answer
Direct answer
Risk scores
| CVSS metric | What it means |
|---|---|
| Attack vector (AV:N) | Network: reachable remotely |
| Attack complexity (AC:H) | High complexity |
| Attack requirements (AT:P) | Attack requirements present |
| Privileges required (PR:N) | No privileges required |
| User interaction (UI:P) | Passive user interaction |
| Confidentiality (VC:N) | No confidentiality impact |
| Integrity (VI:N) | No integrity impact |
| Availability (VA:H) | High availability impact |
CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H/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
About Openvpn
CVE-2026-11771 affects Openvpn, a product from Openvpn. Before acting, confirm where Openvpn runs in your estate, who owns it and whether it is reachable from the internet, because exposure decides real risk more than the score alone.
What the flaw is
In plain terms: OpenVPN version 2.1.0 through 2.6.20 and 2.7_alpha1 through 2.7.4 allows attackers via an off-by-one buffer write in the NTLM proxy authentication to potentially cause a crash via a crafted NTLM response from a malicious proxy server
The weakness class is Stack Buffer Overflow. A write past the end of a stack buffer can corrupt control data.
Based on its CVSS vector, the flaw can be reached over the network, needs no login, and relies on a user taking an action. Apply the vendor fix and confirm exposure on internet facing and business critical assets first.
Affected versions and timeline
| Field | Detail |
|---|---|
| Product | Openvpn |
| Affected versions | Openvpn from 2.1.0 before 2.6.21; Openvpn from 2.7 before 2.7.5 |
| Published | Jul 30, 2026 |
| Last modified | Aug 5, 2026 |
| Added to CISA KEV | Not listed |
| Assigning CNA | security@openvpn.net |
How to detect it
- Inventory every instance of Openvpn and record the running version against the affected range above.
- Check external attack surface scans for internet facing instances of the component.
- Review logs on affected systems for unusual requests, errors or new processes around the vulnerable function.
- Confirm with an authenticated vulnerability scan once your scanner has a check for this CVE.
How to fix it
- Apply the fixed version of Openvpn named in the vendor advisory.
- If patching must wait, restrict network access to the affected service and put it behind authentication or a web application firewall rule.
- Rescan after the change to prove the exposure is gone, then close the ticket.
CTEM action plan
| CTEM stage | What to do for this CVE |
|---|---|
| Scope | Add every business service that depends on Openvpn to the current CTEM cycle. |
| Discover | Find all instances, including shadow and cloud deployments, and record versions and exposure. |
| Prioritize | Rank using EPSS and CVSS together with asset exposure and business impact. |
| Validate | Confirm the flaw is reachable and exploitable in your environment and that compensating controls work. |
| Mobilize | Assign the fix to the asset owner with a due date matched to the priority, then verify closure. |
CWE References
- CWE-121: Stack Buffer Overflow More CVEs with this weakness
- CWE-193 More CVEs with this weakness
- CWE-787: Out of Bounds Write More CVEs with this weakness
Technical References
Frequently asked questions
Related CVEs
A memory leak in the tls-crypt-v2 client key extraction in OpenVPN 2.5.0 through 2.6.20 and 2.7_alpha1 through 2.7.4 allows remote attackers to cause a denial of service (memory exhaustion) via a flood of crafted packets
Privilege escalation via background service of OpenVPN Connect 3.5.1 through 3.8.1 on macOS allows attackers to execute arbitrary commands with elevated privileges via local IPC channel
Stack buffer overflow vulnerability in D-Link DIR-513 v1.10 via the curTime parameter to goform/formSetDomainFilter.
Stack buffer overflow vulnerability in D-Link DIR-513 v1.10 via the curTime parameter to goform/formSetPortTr.
ALGO 8180 IP Audio Alerter SIP INVITE Alert-Info Stack-based Buffer Overflow Remote Code Execution Vulnerability. This vulnerability allows remote attackers to execute arbitrary code on affected installations of ALGO 8180 IP Audio Alerter devices. Authentication is not required to exploit this vulnerability. The specific flaw exists within the handling of the Alert-Info header of SIP INVITE requests. The issue results from the lack of proper validation of the length of user-supplied data prior to copying it to a fixed-length stack-based buffer. An attacker can leverage this vulnerability to execute code in the context of the device. Was ZDI-CAN-28301.
In Tenda AC7 v15.03.06.44, the wanSpeed parameter of the route /goform/AdvSetMacMtuWan has a stack buffer overflow vulnerability that can lead to remote arbitrary code execution.
Earn your free CTEM certification.
Learn to scope, prioritize, validate and mobilize fixes for CVEs like CVE-2026-11771 with a free CTEM certification.
Beginner / Practitioner / Program Leader
Explore certifications