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PatchSiren cyber security CVE debrief

CVE-2026-11771 OpenVPN CVE debrief

OpenVPN versions 2.1.0 through 2.6.20 and 2.7_alpha1 through 2.7.4 are vulnerable to an off-by-one buffer write issue related to NTLM proxy authentication. This could potentially cause a crash via a crafted NTLM response from a malicious proxy server. The CVSS score for this vulnerability is 7, indicating high severity. OpenVPN has addressed this issue in versions 2.6.21 and 2.7.5. Users and administrators should be aware of this vulnerability and take steps to mitigate it, including inventorying OpenVPN installations, applying patches or updates, and monitoring for suspicious activity.

Vendor
OpenVPN
Product
Unknown
CVSS
HIGH 7
CISA KEV
Not listed in stored evidence
Original CVE published
2026-07-30
Original CVE updated
2026-08-05
Advisory published
2026-07-30
Advisory updated
2026-08-05

Who should care

OpenVPN users and administrators should be aware of this vulnerability and take steps to mitigate it. This includes inventorying OpenVPN installations, applying patches or updates, and monitoring for suspicious activity.

Technical summary

The CVE-2026-11771 vulnerability is an off-by-one buffer write issue in OpenVPN versions 2.1.0 through 2.6.20 and 2.7_alpha1 through 2.7.4. This vulnerability is related to NTLM proxy authentication and could potentially cause a crash via a crafted NTLM response from a malicious proxy server. The CVSS score for this vulnerability is 7, indicating high severity. OpenVPN has addressed this issue in versions 2.6.21 and 2.7.5.

Defensive priority

OpenVPN users should prioritize patching due to the high CVSS score of 7 and potential for crash via crafted NTLM response.

Recommended defensive actions

  • Inventory OpenVPN installations to identify potentially affected versions.
  • Apply patches or updates to OpenVPN to address the vulnerability.
  • Monitor for suspicious NTLM authentication attempts.
  • Implement compensating controls, such as network segmentation or access restrictions.
  • Review OpenVPN configurations for potential exposure.
  • Verify patch deployment and system integrity.
  • Track vulnerability mitigation progress and report to stakeholders.

Evidence notes

The CVE-2026-11771 record indicates an off-by-one buffer write vulnerability in OpenVPN versions 2.1.0 through 2.6.20 and 2.7_alpha1 through 2.7.4. The vulnerability is related to NTLM proxy authentication and could potentially cause a crash via a crafted NTLM response from a malicious proxy server. The CVSS score is 7, indicating a high severity. OpenVPN has released updates to address this issue, specifically versions 2.6.21 and 2.7.5.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-11771 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-11771

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-11771 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-11771

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.